Prepare ConfigKit v0.4.2 release

.gitignore

@@ -25,6 +25,9 @@ go.work.sum
 # env file
 .env
 
+# Local codebase-memory tooling artifacts
+/.codebase-memory/
+
 # ---> Linux
 *~
 
@@ -81,4 +84,3 @@ Temporary Items
 .history/
 
 # Built Visual Studio Code Extensions
-*.vsix

AGENTS.md

@@ -1,2 +1,25 @@
-Please review `docs/development.md` for initial orientation in this repository
-and follow its task-specific reading guide.
+<!-- codebase-memory-mcp:start -->
+# Codebase Knowledge Graph (codebase-memory-mcp)
+
+This project uses codebase-memory-mcp to maintain a knowledge graph of the codebase.
+ALWAYS prefer MCP graph tools over grep/glob/file-search for code discovery.
+
+## Priority Order
+1. `search_graph` — find functions, classes, routes, variables by pattern
+2. `trace_path` — trace who calls a function or what it calls
+3. `get_code_snippet` — read specific function/class source code
+4. `query_graph` — run Cypher queries for complex patterns
+5. `get_architecture` — high-level project summary
+
+## When to fall back to grep/glob
+- Searching for string literals, error messages, config values
+- Searching non-code files (Dockerfiles, shell scripts, configs)
+- When MCP tools return insufficient results
+<!-- codebase-memory-mcp:end -->
+
+Start with `docs/development.md` for orientation and use its policy reading guide
+to select the policies applicable to the task. Do not read the entire suite by
+default.
+
+Read and follow `docs/policy/agents.md` before recommending, planning, or
+implementing repository changes.

COPYRIGHT

@@ -0,0 +1,25 @@
+ConfigKit
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: LGPL-3.0-or-later
+
+This library is free software: you can redistribute it and/or modify it
+under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+The GNU Lesser General Public License version 3 and its incorporated
+GNU General Public License version 3 text are provided in LICENSE.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Lesser General Public License for more details.
+
+Third-party code and assets are subject to their respective license terms.
+
+Policy documents adapted from Standard Repository Policies, the root AGENTS.md
+orientation, and the Policy Reading Guide in docs/development.md remain licensed
+under CC-BY-SA-4.0. See docs/oss/attribution.md for the affected material,
+upstream credit, and license links.

README.md

@@ -2,9 +2,45 @@
 
 An opinionated Go library for applications that use YAML configuration files.
 
-ConfigKit is in pre-implementation. This repository currently contains its design
-and contributor policies; no usable Go library has been implemented yet.
+Linux is release-validated; macOS support is best-effort. See the
+[platform support policy](docs/policy/release.md#platform-support) for details.
 
-The [initial target design](docs/roadmap/initial.md) describes planned behavior.
-The [implementation plan](docs/roadmap/implementation.md) owns the pending stages.
-See the [development guide](docs/development.md) for repository orientation.
+ConfigKit's initial loader accepts one strict YAML
+source (or explicit defaults-only input), optionally traverses explicit path and glob
+imports, strictly composes their disjoint definitions, applies typed defaults, and
+can overlay one selected fixed overlay and check an application schema version. It
+returns detached metadata and safe diagnostics.
+Applications may perform audited defaulting and normalization through a resolver,
+then report domain errors and warnings through read-only semantic validation. Secret
+tags and a path predicate drive deterministic redacted effective YAML. Typed secret
+references resolve environment names before validation, and explicit
+secrets-directory bootstrap is available as a separate startup operation. Explicit
+CLI override records apply above overlays. Value explanation is available through
+detached structured records and deterministic redacted output.
+
+```go
+type Config struct {
+    Enabled bool `yaml:"enabled"`
+    Workers int  `yaml:"workers"`
+}
+
+func ReadConfig(path string) (Config, error) {
+    result, err := configkit.Load[Config](configkit.File(path))
+    if err != nil {
+        return Config{}, err
+    }
+    return result.Config, nil
+}
+```
+
+The [configuration contract](docs/config.md) describes implemented behavior. The
+[consumer adoption guide](docs/consumers/README.md) provides maintained Narratio-,
+Notarius-, WeatherReporter-, and Seriatim-shaped examples and migration guidance.
+The [deferred scope](docs/roadmap/deferred.md) records deliberate exclusions. See the
+[development guide](docs/development.md) for repository orientation and the
+[release procedure](docs/release.md) for maintainer-only candidate and publication
+steps.
+
+ConfigKit code is licensed under the [LGPL v3.0 or later](COPYRIGHT).
+
+[Open Source attribution notices](docs/oss/attribution.md) are available.

conversion.go

@@ -0,0 +1,133 @@
+package configkit
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/engine"
+
+func fromEngineLocation(value engine.Location) Location {
+	return Location{SourceID: value.SourceID, Line: value.Line, Column: value.Column}
+}
+func toEngineLocation(value Location) engine.Location {
+	return engine.Location{SourceID: value.SourceID, Line: value.Line, Column: value.Column}
+}
+func fromEngineLocationPointer(value *engine.Location) *Location {
+	if value == nil {
+		return nil
+	}
+	result := fromEngineLocation(*value)
+	return &result
+}
+func toEngineLocationPointer(value *Location) *engine.Location {
+	if value == nil {
+		return nil
+	}
+	result := toEngineLocation(*value)
+	return &result
+}
+func fromEngineLocations(values []engine.Location) []Location {
+	if values == nil {
+		return nil
+	}
+	result := make([]Location, len(values))
+	for i := range values {
+		result[i] = fromEngineLocation(values[i])
+	}
+	return result
+}
+func toEngineLocations(values []Location) []engine.Location {
+	if values == nil {
+		return nil
+	}
+	result := make([]engine.Location, len(values))
+	for i := range values {
+		result[i] = toEngineLocation(values[i])
+	}
+	return result
+}
+func fromEngineSourceInfo(value engine.SourceInfo) SourceInfo {
+	return SourceInfo{ID: value.ID, Label: value.Label, Path: value.Path, Layer: Layer(value.Layer), ImportedFrom: fromEngineLocationPointer(value.ImportedFrom)}
+}
+func toEngineSourceInfo(value SourceInfo) engine.SourceInfo {
+	return engine.SourceInfo{ID: value.ID, Label: value.Label, Path: value.Path, Layer: engine.Layer(value.Layer), ImportedFrom: toEngineLocationPointer(value.ImportedFrom)}
+}
+func fromEngineOrigin(value engine.Origin) Origin {
+	return Origin{Layer: Layer(value.Layer), Locations: fromEngineLocations(value.Locations), Operation: ChangeKind(value.Operation)}
+}
+func toEngineOrigin(value Origin) engine.Origin {
+	return engine.Origin{Layer: engine.Layer(value.Layer), Locations: toEngineLocations(value.Locations), Operation: engine.ChangeKind(value.Operation)}
+}
+func fromEngineDiagnostic(value engine.Diagnostic) Diagnostic {
+	return Diagnostic{Code: Code(value.Code), Severity: Severity(value.Severity), Path: fromEnginePath(value.Path), Message: value.Message, Primary: fromEngineLocationPointer(value.Primary), Related: fromEngineLocations(value.Related)}
+}
+func toEngineDiagnostic(value Diagnostic) engine.Diagnostic {
+	return engine.Diagnostic{Code: engine.Code(value.Code), Severity: engine.Severity(value.Severity), Path: toEnginePath(value.Path), Message: value.Message, Primary: toEngineLocationPointer(value.Primary), Related: toEngineLocations(value.Related)}
+}
+func toEngineDiagnostics(values []Diagnostic) []engine.Diagnostic {
+	if values == nil {
+		return nil
+	}
+	result := make([]engine.Diagnostic, len(values))
+	for i := range values {
+		result[i] = toEngineDiagnostic(values[i])
+	}
+	return result
+}
+func fromEngineFieldInfo(value engine.FieldInfo) FieldInfo {
+	return FieldInfo{Explicit: value.Explicit, Null: value.Null, Origin: fromEngineOrigin(value.Origin)}
+}
+func fromEngineChange(value engine.Change) Change {
+	result := Change{Path: fromEnginePath(value.Path), Origin: fromEngineOrigin(value.Origin), Reasons: append([]string(nil), value.Reasons...)}
+	if value.Previous != nil {
+		result.Previous = make([]Origin, len(value.Previous))
+		for i := range value.Previous {
+			result.Previous[i] = fromEngineOrigin(value.Previous[i])
+		}
+	}
+	if value.Dependencies != nil {
+		result.Dependencies = make([]Path, len(value.Dependencies))
+		for i := range value.Dependencies {
+			result.Dependencies[i] = fromEnginePath(value.Dependencies[i])
+		}
+	}
+	return result
+}
+
+func fromEngineValueSnapshot(value engine.ValueSnapshot) ValueSnapshot {
+	return ValueSnapshot{Present: value.Present, Redacted: value.Redacted, YAML: value.YAML}
+}
+
+func fromEngineValueChange(value engine.ValueChange) ValueChange {
+	result := ValueChange{
+		Before:  fromEngineValueSnapshot(value.Before),
+		After:   fromEngineValueSnapshot(value.After),
+		Origin:  fromEngineOrigin(value.Origin),
+		Reasons: append([]string(nil), value.Reasons...),
+	}
+	if value.Dependencies != nil {
+		result.Dependencies = make([]Path, len(value.Dependencies))
+		for index := range value.Dependencies {
+			result.Dependencies[index] = fromEnginePath(value.Dependencies[index])
+		}
+	}
+	return result
+}
+
+func fromEngineExplanation(value engine.Explanation) Explanation {
+	result := Explanation{
+		Path:      fromEnginePath(value.Path),
+		Effective: fromEngineValueSnapshot(value.Effective),
+		Origin:    fromEngineOrigin(value.Origin),
+	}
+	if value.History != nil {
+		result.History = make([]ValueChange, len(value.History))
+		for index := range value.History {
+			result.History[index] = fromEngineValueChange(value.History[index])
+		}
+	}
+	if value.SecretReference != nil {
+		result.SecretReference = &SecretReferenceInfo{Name: value.SecretReference.Name}
+	}
+	return result
+}
+
+func fromEngineSecretFileResult(value engine.SecretFileResult) SecretFileResult {
+	return SecretFileResult{Name: value.Name, Path: value.Path, Status: SecretFileStatus(value.Status), ExistingEmpty: value.ExistingEmpty}
+}

diagnostic.go

@@ -0,0 +1,57 @@
+package configkit
+
+import (
+	"io"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/engine"
+)
+
+// LoadError reports safe structured diagnostics for a failed configuration load.
+// It intentionally does not expose or unwrap parser and application errors.
+type LoadError struct{ value *engine.LoadError }
+
+// Error implements error without rendering diagnostic messages or input values.
+func (e *LoadError) Error() string {
+	if e == nil || e.value == nil {
+		return "configkit: configuration load failed"
+	}
+	return e.value.Error()
+}
+
+// Diagnostics returns a deep copy of the error's canonical diagnostics.
+func (e *LoadError) Diagnostics() []Diagnostic {
+	if e == nil || e.value == nil {
+		return nil
+	}
+	values := e.value.Diagnostics()
+	if values == nil {
+		return nil
+	}
+	result := make([]Diagnostic, len(values))
+	for i := range values {
+		result[i] = fromEngineDiagnostic(values[i])
+	}
+	return result
+}
+
+// Sources returns a deep copy of sources discovered before loading failed.
+func (e *LoadError) Sources() []SourceInfo {
+	if e == nil || e.value == nil {
+		return nil
+	}
+	values := e.value.Sources()
+	if values == nil {
+		return nil
+	}
+	result := make([]SourceInfo, len(values))
+	for i := range values {
+		result[i] = fromEngineSourceInfo(values[i])
+	}
+	return result
+}
+
+// WriteDiagnostics writes diagnostics in canonical order. It escapes terminal
+// control characters and propagates writer errors, including short writes.
+func WriteDiagnostics(output io.Writer, diagnostics []Diagnostic) error {
+	return engine.WriteDiagnostics(output, toEngineDiagnostics(diagnostics))
+}

doc.go

@@ -0,0 +1,9 @@
+// Package configkit provides deterministic, application-owned configuration
+// loading for Go programs.
+//
+// Load supports file, byte, reader, and explicit no-input sources with strict YAML,
+// typed defaults, imports, overlays, CLI overrides, schema-version checks, detached
+// metadata, recorded application resolution, typed secret references, safe effective
+// rendering, read-only semantic validation, and structured load errors. The
+// configuration contract is documented in docs/config.md.
+package configkit

docs/adr/0001-separate-composition-and-overlay.md

@@ -20,8 +20,8 @@ Use distinct strict-composition and intentional-overlay operations. Composition
 rejects conflicting definitions; overlay provides explicit precedence. Keep the
 operations opinionated rather than adding arbitrary per-field merge strategies.
 The [architecture policy](../policy/architecture.md) owns the governing boundary;
-the [target design](../roadmap/initial.md#composition-and-overlay) owns the planned
-operation table until its current contract lands.
+the [current configuration contract](../config.md#strict-document-composition) owns
+the operation table and selected-profile overlay behavior.
 
 ## Alternatives considered
 

docs/adr/0002-own-yaml-semantics.md

@@ -20,7 +20,8 @@ ConfigKit defines its supported YAML policy and keeps parser integration private
 Application types and diagnostics must not require parser-specific public types.
 Use a small internal boundary rather than a general parser/provider framework.
 The [architecture policy](../policy/architecture.md) owns this constraint; the
-[target design](../roadmap/initial.md#yaml-and-scalar-policy) owns planned syntax.
+[current YAML document](../config.md#yaml-documents) and
+[scalar](../config.md#scalars) contracts own the implemented syntax.
 
 ## Alternatives considered
 

docs/adr/0003-preserve-presence-and-resolution-history.md

@@ -22,8 +22,9 @@ values. Keep application defaults and normalization application-owned, but recor
 resolution changes so final inspection and metadata describe the actual resolved
 snapshot. Do not promise language-enforced immutability of exported Go values.
 The [architecture policy](../policy/architecture.md) owns these invariants; the
-[target design](../roadmap/initial.md#recorded-resolution-and-validation) owns the
-planned recording mechanism and ownership semantics.
+[current resolution contract](../config.md#recorded-application-resolution) and
+[ownership contract](../config.md#typed-projection-and-ownership) own the implemented
+recording mechanism and ownership semantics.
 
 ## Alternatives considered
 

docs/adr/0004-secret-references-and-explicit-bootstrap.md

@@ -21,8 +21,9 @@ Existing environment variables win even when empty. Report skipped files and
 partial failures without values. Keep bootstrap provenance separate from later
 lookup provenance rather than imply an unchanged environment between calls.
 General environment-variable configuration overlays are not on the roadmap.
-The [feature roadmap](../roadmap/initial.md#secret-references-and-explicit-bootstrap)
-owns the unimplemented contract; stages remain in the implementation plan.
+The [current reference contract](../config.md#typed-secret-references) and
+[bootstrap contract](../config.md#explicit-secrets-directory-bootstrap) own the
+implemented behavior.
 
 ## Alternatives considered
 

docs/adr/0005-explicit-overrides-and-safe-explanation.md

@@ -19,8 +19,9 @@ node tree before typed decoding, retaining the existing parser adapter boundary.
 Recorded domain resolution follows input selection. Provide safe structured
 historical values and an explanation renderer in the initial release, building
 on ADR 0003's presence and audited resolution decision. Applications own commands.
-The [feature roadmap](../roadmap/initial.md#cli-overrides) owns the exact override
-contract and [explanation contract](../roadmap/initial.md#historical-value-explanation).
+The [current override contract](../config.md#explicit-cli-overrides) and
+[explanation contract](../config.md#historical-value-explanation) own the implemented
+behavior.
 
 ## Alternatives considered
 

docs/adr/0006-public-facade.md

@@ -0,0 +1,61 @@
+# ADR 0006: Keep the public facade root-owned
+
+## Status
+
+Accepted and implemented on 2026-09-12.
+
+## Date
+
+2026-09-12
+
+## Context
+
+The root `configkit` package formerly combined the supported consumer API with
+loading, decoding, inspection, and rendering machinery. That made ordinary
+consumer navigation harder and risked exposing implementation details through
+future public declarations. Moving files alone would not preserve the identity,
+method sets, callbacks, ownership rules, or reflection-sensitive behavior of the
+root's public types.
+
+## Decision
+
+Keep `configkit` as the sole supported consumer import path and keep all public
+named types defined there. Lifecycle machinery lives in a cohesive
+`internal/engine`; the root facade holds private engine state and forwards
+deliberately selected methods. The dependency direction is root to engine and
+its supporting internal packages. Internal production packages do not import the
+root package.
+
+The facade will use root-owned wrappers and explicit private conversions. It
+will not use public aliases to engine types, anonymous embedding that promotes
+engine methods, public engine types in signatures or fields, or public bridge
+methods. Existing document and YAML boundaries remain intact.
+
+The migration used a temporary internal candidate facade while the unchanged root
+remained the only production entry point. That duplication was a bounded
+relocation mechanism, not a second supported package, feature path, or runtime
+selection mechanism; the final cutover removed it and the old root implementation.
+
+The [architecture policy](../policy/architecture.md#public-api-and-dependency-direction)
+owns the binding boundary. The [component overview](../internal/overview.md)
+describes the implemented layout; the [development guide](../development.md)
+locates the completed roadmap and implementation history.
+
+## Alternatives considered
+
+- Alias root types to engine types: reduces forwarding, but makes the engine's
+  exported method set and type ownership part of the consumer API.
+- Keep all machinery in the root package: avoids migration work, but leaves the
+  public boundary difficult to navigate and easy to expand accidentally.
+- Introduce a generic adapter or registration framework: could reduce some
+  handwritten conversions, but adds machinery and obscures the ownership rules
+  this boundary needs to preserve.
+
+## Consequences
+
+The refactor carries explicit forwarding and conversion work, especially for
+callbacks, detached records, source ownership, frozen inspection, and the
+exact-type secret bridge. Public compatibility must be verified by behavior and
+external-package evidence rather than inferred from package names. Internal
+exports remain implementation surfaces, and the completed architecture will
+have one engine and one root facade.

docs/config.md

@@ -0,0 +1,770 @@
+# Configuration Input Contract
+
+This document owns ConfigKit's currently implemented source-input, YAML syntax,
+schema, typed-decoding, loading, metadata, redaction, rendering, and ownership
+contracts. The parser, owned document representation, and decoder remain private
+behind the public loading lifecycle.
+
+## Sources
+
+ConfigKit exposes opaque sources through these constructors:
+
+| Constructor | Current contract |
+| --- | --- |
+| `File(path)` | Requires a nonempty path, opens a regular file for each consumption, and closes only the library-owned file handle. Missing, inaccessible, unreadable, directory, and other nonregular inputs fail. |
+| `Bytes(label, data)` | Requires a nonempty, non-secret diagnostic label and snapshots bytes during construction. Later caller mutation cannot affect the source. |
+| `Reader(label, input)` | Requires a nonempty, non-secret label and non-nil reader. The reader is claimed once across all copies of the source, consumed but never closed, and cannot be reused. |
+| `NoSource()` | Selects defaults-only loading, creates no source record, and marks no paths explicit. |
+
+The zero `Source` is invalid. Constructor argument failures are retained inside the
+opaque source and become safe structured diagnostics when the source is consumed.
+File sources can observe file changes between consumptions; byte sources cannot.
+
+Each source is limited to 8 MiB. A load using imports or an active overlay is limited
+to 64 MiB across all accepted sources, 1,024 accepted sources, 64 active import
+edges, and 1,000,000 input nodes in aggregate. Glob expansion separately permits
+1,000,000 visited directory entries, including nonmatches. Reads request at most the
+remaining allowance plus one byte so excess data is rejected rather than silently
+truncated. Data returned together with a read error is not accepted as partial input.
+
+## Single-source loading
+
+`Load[T](source, options...)` accepts zero or one `Options[T]`. The configuration
+root `T` must satisfy the application schema contract below. With no options it
+starts from the Go zero value. A `Definition[T].Defaults` factory, when supplied,
+runs exactly once after successful source parsing, schema construction, optional
+schema-version checking, and selected-overlay loading. Its result is detached before
+input is applied. Resolver-provided mutable values are detached before secret lookup
+and validation, and a final detached copy prevents equal-valued aliases introduced
+by validators from escaping into the returned configuration. The publication copy
+preserves already validated secret state without rereading the environment.
+
+The current lifecycle is:
+
+```text
+validate options → parse the selected source → traverse/compose enabled imports
+  → build schema → check the optional application version → apply a selected overlay
+  → apply explicit CLI overrides → create and clone defaults → strictly decode
+  → recorded application resolution
+  → resolve typed secret references → semantic validation → classify secrets
+  → snapshot configuration and metadata
+```
+
+`File`, `Bytes`, and `Reader` each contribute the first base source with deterministic
+ID `source-1`; enabled imports continue in depth-first order as `source-2` onward.
+`NoSource` skips parsing, supplies an absent version to a configured version checker,
+contributes no source, and continues through defaults, decode, and projection. A
+missing file remains an error; it is never interpreted as no input.
+
+The current `Options` boundary accepts a defaults factory, `VersionRule`, resolver,
+semantic validator, explicit path and glob imports, one selected overlay, and
+filesystem context. It also accepts explicit CLI override records, static secret
+tags, and a dynamic path predicate. `NoSource` rejects imports, active overlays,
+and filesystem context as invalid combinations but accepts overrides. Input
+containing a reserved `configkit` mapping key is rejected while imports are
+disabled.
+
+Every source, options, schema, version, defaults, decode, resolution, or validation
+failure returns a nil result and a `*LoadError`. Successful results contain caller-owned `Config`, detached
+`Metadata`, a defensive source list, and defensive nonfatal diagnostics. Mutating
+the returned configuration or inspection records cannot alter ConfigKit's private
+snapshot. ConfigKit performs no logging. `Result.WriteEffective` exposes only the
+frozen redacted projection.
+
+### Application schema versions
+
+`VersionRule` declares a semantic path and non-nil checker. Before defaults or typed
+decoding, the checker receives a `Version` preserving absent, explicit null, string,
+or strict decimal-integer input. Strings and integers supply their exact spelling in
+`Version.Text`; ConfigKit does not impose a machine-integer range. Fractional or
+exponent numbers, booleans, mappings, and sequences produce `version.type`, and the
+checker does not run. ConfigKit does not interpret the text or impose a universal
+version path.
+
+Integer versions use the strict grammar `^-?(0|[1-9][0-9]*)$`. Their spelling is
+preserved exactly, including `-0`, and application policy decides which identifiers
+are supported. A numeric version has no built-in `int64` range limit. Existing parser
+policy still rejects leading zeroes, leading plus signs, hexadecimal notation, and
+other non-JSON scalar forms before version checking.
+
+At exactly the configured semantic path, accepted integer input can decode into a
+plain Go string or named string without a text codec, including pointer wrappers.
+This is a load-local exception: siblings and unrelated fields, dynamic values,
+integer and float destinations, durations, `Secret`, and text codecs retain ordinary
+strict decoding. The retained source and history stay numeric while typed projection
+and effective YAML contain the resulting string; explanation records this through
+the normal decoding reconciliation event. Fragment, overlay, and CLI ownership
+protections apply before this conversion.
+
+The checker reports safe, value-free errors and warnings through `Validation.Error`
+and `Validation.Warning`; ConfigKit resolves primary and related paths to exact or
+nearest input locations. Reported errors fail loading. If the checker returns an
+error without reporting one, ConfigKit emits a generic `version.hook_failed`
+diagnostic and suppresses the returned error text. Warnings alone are retained on a
+successful result. Callback panics remain programming failures.
+
+### Layered metadata
+
+`Result.Metadata` describes every final canonical path. Queries retain explicit
+key/index distinctions using actual effective and historical container shapes;
+only parsed numeric tokens are resolved contextually. A descendant that never
+existed is not historical merely because an atomic ancestor was replaced. Exact surviving input paths
+are explicit and have a base or overlay origin; omitted paths have a default origin.
+An explicit parent mapping does not make omitted children explicit. Null state and
+available source coordinates are retained. `History` records the Go-zero or application
+default baseline followed by exact base or overlay definitions, including
+equal-valued input. Overlay replacement removes displaced descendants from effective
+metadata while retaining their base definition and the parent replacement operation
+in history. All metadata queries and returned nested records are detached.
+
+`Metadata.HistoricalPaths` enumerates observed paths, including removed paths,
+without reloading input or resolving unselected credentials. Consumers can use
+it with `History` to validate ownership of declarations hidden by an overlay;
+domain ownership rules remain application responsibilities. The method's Go
+documentation in [metadata.go](../metadata.go) defines enumeration and path-ordering
+details.
+
+History is chronological: a path can have a synthetic default record, its exact base
+definition, an overlay replacement, and a recorded resolution operation. A descendant
+query uses the ancestor's path for a whole-container or whole-sequence replacement;
+the descendant can therefore retain history after `Lookup` stops reporting it as
+effective. Equal-valued input is still an explicit base definition, while a derived
+value for absent input remains non-explicit.
+
+A mapping assembled from the selected file and imports has one composite base origin
+whose locations retain source traversal order. A mapping also visited by an overlay
+has an overlay-layer composite origin with the lower contributing locations followed
+by the overlay location; an empty mapping is still an explicit container even though
+it contributes no children. Resolution origins are synthetic: they have layer
+`resolution`, no fabricated file location, and a `derived_default` or `normalization`
+operation. Reasons and dependency paths retain first occurrence order with duplicates
+removed. Source records remain ordered as selected source, depth-first imports, the
+selected overlay, then synthetic CLI records in supplied order.
+
+### Secret classification and effective rendering
+
+Secret classification combines `configkit:"secret"` field tags with the optional
+pure `Definition.Secret(Path) bool` predicate. Tags on concrete structs inside
+supported dynamic values are retained in typed projections, including superseded
+defaults and pre-resolution values. A tagged or predicate-classified
+container makes all descendants sensitive. ConfigKit evaluates final and historical
+paths, so replacing or deleting a definition does not erase its classification. The
+predicate can add sensitivity but cannot declassify a tagged path.
+
+Recorded resolution dependencies propagate sensitivity to their derived target.
+Propagation reaches a fixed point, so record/map iteration order does not affect the
+result and dependency cycles terminate. A dependency on a classified descendant or
+on a container that contains one is treated conservatively as sensitive. Applications
+must classify secret-producing transformations whose dependencies are not recorded.
+
+`Result.WriteEffective` writes the frozen resolved snapshot as deterministic redacted
+YAML. Mappings sort by decoded key string, sequences retain order, indentation is two
+spaces with noncompact sequence indentation, line endings are LF, the document has no
+start or end marker, and output ends with a newline. Nil pointers/maps/slices remain
+`null`; non-nil empty maps and sequences remain `{}` and `[]`. A secret root is
+replaced by the quoted string `'[REDACTED]'`. Redacted output is intended for
+inspection and is not promised to be reloadable.
+
+Rendering uses only a safe adapter tree built from the already completed canonical
+typed projection. It does not invoke application YAML marshal hooks or text codecs;
+all text-codec projection has succeeded before `Load` returns. Caller mutation of
+`Result.Config` cannot change later output. Writer failures, including short writes,
+are returned and may leave partial redacted output; internal dumper failures are
+translated to a fixed safe error. There is no unredacted rendering option and
+ConfigKit performs no implicit logging.
+
+`Result.Config` is the explicit trusted boundary and contains ordinary typed values,
+including secrets. Metadata records, diagnostics, and load errors contain no
+configuration values. Explanation snapshots deliberately expose non-secret
+configuration history after applying the redaction contract below. Applications
+must still keep source labels, resolution reasons, and diagnostic messages value-free
+because ConfigKit cannot infer and sanitize secrets embedded in arbitrary application
+prose.
+
+### Historical-value explanation
+
+`Result.Explain(path)` returns a detached `Explanation` for any known effective or
+historical path. Its effective value and each chronological before/after value are
+`ValueSnapshot` records containing deterministic YAML text rather than mutable Go or
+parser values. `Present=false` with empty YAML means absence or deletion; explicit
+null is present and renders as `null`. The history starts with the canonical typed
+application-default or Go-zero baseline, then includes only relevant base sources in
+traversal order, the selected overlay, supplied CLI records, and audited net
+resolution operations. Overlapping parent/child resolution records are rendered
+as one net subtree event with combined reasons and dependencies, rather than
+pretending that the recorded assignments ran in lexical order. Explicit equal
+writes remain visible. When input replay
+differs from the final typed input, a `ChangeDecoding` event records the transition
+before domain resolution. Its origin retains the decoded path's source/default
+attribution; its reason identifies static-default retention and canonical decoding.
+This built-in inspection operation is not accepted by `Resolution.Record`.
+
+Base, overlay, and CLI history preserves the policy-validated input representation,
+including a superseded value that could not have decoded into the final Go field.
+Baseline, effective, and resolution values use canonical typed projection. A
+decoding event bridges replayed input and canonical typed values, so intermediate
+null/scalar replacements cannot incorrectly imply permanent default removal. Mapping
+queries reconstruct each source or override contribution, while sequences remain
+atomic: a descendant history identifies its presence before and after the containing
+sequence replacement without implying element-wise merging. Removed paths remain
+explainable; unknown and malformed paths return false.
+
+Every snapshot applies the same historical tag, predicate, and recorded-dependency
+sensitivity closure as effective rendering before YAML is exposed. A redacted scalar
+is the quoted marker `'[REDACTED]'`, and a container snapshot has `Redacted=true` if
+it contains a masked descendant. Typed `Secret` snapshots contain only the configured
+environment name. `SecretReference` reports that name only for a successfully
+resolved effective reference, and is omitted when its path is classified. Credential
+values are never retained in explanation history.
+
+`Result.WriteExplanation(output, path)` renders the safe structured result with the
+canonical JSON-pointer path, canonical-versus-input representation labels, effective
+source, composite locations, chronological values, resolution reasons and
+dependencies, and successful secret-reference lookup attribution. Control characters
+in paths, source identifiers and labels, reasons, dependencies, and reference names
+are escaped. An unknown path returns a fixed safe error before writing anything;
+writer errors and short writes are returned and may leave partial output. There is no
+unredacted mode.
+
+Retained history consists of immutable source applications and audited subtree
+deltas, rather than a full tree copy per field. Shared nodes count once toward a
+4,000,000-node retained-history limit; exceeding it fails loading with
+`explain.limit_exceeded`. Replaying one requested path is performed on demand, and
+the returned YAML strings and nested records cannot mutate later explanations.
+
+Application commands should render the separate `SecretsReport` immediately after
+an explicit `LoadSecretsDir` bootstrap, then use `WriteDiagnostics`,
+`WriteEffective`, or `WriteExplanation` on the later load result as appropriate.
+ConfigKit does not infer bootstrap outcomes from a secret reference and does not
+bundle these independent reports into a command framework.
+
+## Typed secret references
+
+Credential-bearing fields use the opaque `Secret` type and store an environment
+variable name in YAML, such as `api_key: OPENROUTER_API_KEY`. `SecretEnv(name)`
+constructs the same unresolved reference for application defaults or recorded
+resolution. Names must match `[A-Za-z_][A-Za-z0-9_]*`; they are public
+configuration and remain visible through `EnvName`, canonical projection, history,
+and effective output unless the path is separately classified for redaction.
+
+A non-pointer `Secret` is required. An absent, null, or invalid reference, or an
+unset or empty environment value, fails with a safe `secret.*` diagnostic at the
+configuration path. `*Secret` is optional only when nil; every non-nil reference
+must resolve to a nonempty value. Secret references work in typed structs, maps,
+pointers, slices, and arrays. A dynamic `any` value does not establish secret
+semantics and cannot contain `Secret`; applications must use a typed slot.
+
+ConfigKit resolves only the effective names after recorded application resolution
+and before semantic validation. Each unique name is read with `os.LookupEnv` once
+per load. Validation can inspect the credential through the deliberately named
+`Value()` accessor and distinguish success with `IsResolved()`. Later loads read
+the environment again, and cloned defaults are rebuilt from names so a previously
+resolved result cannot retain a stale credential. `Load` never writes to the
+environment.
+
+Credential bytes are held only in the per-load lookup state and the trusted returned
+configuration, and are returned only by `Value`. Secret formatting uses a safe
+public-name representation, JSON marshals only the name, and projection, metadata,
+histories, diagnostics, effective output,
+and resolution snapshots never retain the credential. Validation remains read-only:
+in addition to ordinary projected-value comparison, ConfigKit checks the private
+resolved state against this load's lookup result. Validator mutation checks also
+reject changes to projected field sensitivity, even when a replacement dynamic
+concrete type preserves the same textual values. Applications must keep their
+validation messages value-free and must not include `Value()` in diagnostics.
+
+For example, a typed pipeline field is declared as:
+
+```go
+type PipelineConfig struct {
+    APIKey configkit.Secret `yaml:"api_key"`
+}
+```
+
+The executable `ExampleSecretEnv` demonstrates loading and inspecting the safe
+reference state without printing its value.
+
+## Explicit secrets-directory bootstrap
+
+`LoadSecretsDir(directory)` is a separate, opt-in startup operation. It is never
+called by `Load`, is not a YAML option, and does not participate in configuration
+validation. Applications choose the native directory path and should invoke the
+operation once before starting concurrent work. The selected path may itself be a
+symlink; ConfigKit resolves it to an existing canonical directory before examining
+its immediate entries.
+
+The bootstrap enumerates at most 1,024 entries, including dot-prefixed entries.
+Entries whose names begin with `.` (files, directories, or symlinks, such as `.git`
+and `.gitignore`) are ignored before name or metadata validation, are never opened,
+and are omitted from the report. Remaining entries are sorted by filename; each
+must have an ASCII environment-variable name and be a regular, nonsymlink
+file. Metadata for all remaining entries is validated before file content is read
+or process state is changed. Existing environment variables win, including variables whose
+value is empty; their files are not opened. Each eligible file is limited to 1 MiB,
+and eligible content is limited to 8 MiB in total. ConfigKit removes exactly one
+terminal LF or CRLF, preserves all other whitespace, accepts an empty value, and
+rejects NUL bytes.
+
+All eligible files are read successfully before application begins. Presence is
+checked again immediately before each `os.Setenv`: a variable populated since
+preflight is skipped. A write failure stops application without rollback, so prior
+writes remain and later eligible entries are `not_applied`. This operation is not
+atomic and does not provide compare-and-set semantics for concurrent environment
+mutation.
+
+`SecretsReport.Entries` returns detached, filename-ordered `SecretFileResult`
+records with `loaded`, `skipped_existing`, `not_applied`, or `failed` status.
+`ExistingEmpty` distinguishes an empty existing winner. `SecretsReport.WriteTo`
+renders only quoted names, canonical paths, statuses, and that empty-state flag;
+it never retains or renders file contents. Failures return the non-nil partial
+report with a `*SecretsError` containing detached `secrets.*` diagnostics and no
+raw filesystem or environment error chain. Applications should retain the report
+alongside the later configuration result and explicitly present blocked and failed
+files when appropriate; ConfigKit stores no implicit global report.
+
+### Recorded application resolution
+
+An optional `Definition.Resolve` callback runs after successful typed decoding. It
+receives the working configuration and a per-load `Resolution` context. The context's
+`IsExplicit` query uses surviving input presence, so explicit false, zero, empty, and
+null are never confused with absence or static defaults.
+
+`Resolution.InputInfo(path)` returns detached effective metadata from the fixed
+decoded entry state, before application resolution runs. It includes retained static
+defaults, preserves explicit null, and uses the same exact semantic path matching as
+`Metadata.Lookup`; missing, malformed, and key/index-shape-mismatched paths return
+false without diagnostics. Its `Explicit` value agrees with `IsExplicit` for every
+found entry path. Resolution changes, additions, removals, and moves do not alter
+this entry view.
+
+`Resolution.Source(id)` returns a detached record for an already acquired source in
+the same load: the main source, imports, selected overlay, and supplied CLI records
+where applicable. Empty and unknown IDs return false. It never reloads input, reads
+the filesystem, resolves symlinks, or looks up credentials. A source path exists
+only when the acquired source has one; defaults and byte, reader, and CLI sources do
+not acquire an invented file path. Applications select a base directory from exact
+origin locations and these source records according to their own policy.
+
+Both queries are callback-scoped like the rest of `Resolution`: nil, zero, or
+retained contexts panic with the fixed closed-context failure outside the callback.
+Returned field and source records are detached and remain usable after callback
+exit; changing them cannot affect later queries, results, or another load.
+
+`Default` assigns and records a derived value only when its path is not explicit.
+`Normalize` always assigns and records. For transformations performed directly by
+application code, `Resolution.Record` declares a derived-default or normalization
+operation; a recorded container covers changes to its descendants. Records require
+a schema-valid path, valid kind, safe nonempty reason, and schema-valid dependency
+paths. Repeated records at one path are coalesced: reasons and dependencies retain
+their first occurrence, the last helper value is authoritative, and any normalization
+makes the combined operation a normalization.
+
+ConfigKit projects the configuration before and after the callback. Every net change
+must have an exact or ancestor record. Helper-assigned values must agree with the
+final value at their declared path, which supports ordinary map-entry copy/writeback
+while detecting forgotten writeback or unrelated targets. Invalid paths, kinds,
+values, records, helper targets, and unrecorded mutations fail the load. Equal-valued
+derived assignments may still record application intent even when there is no
+structural change.
+
+`Resolution.Error` and `Resolution.Warning` attach exact or nearest available input
+locations. Reported errors fail the load; warnings survive on a successful result. A
+returned resolver error adds one generic `resolve.hook_failed` error only when the
+callback did not report an error, and its text is never exposed. Callback panics are
+programming failures. Resolution and validation contexts are callback-scoped; using
+a nil, zero, or retained context outside its active callback panics with fixed,
+value-free text.
+
+Successful records update effective origins and append detached metadata history
+without changing input explicitness. Removed paths leave effective metadata but
+retain history. ConfigKit privately snapshots each recorded before/after subtree for
+later safe explanation; caller mutations of `Result.Config` cannot alter those
+snapshots.
+
+### Semantic validation
+
+An optional `Definition.Validate` callback runs after successful resolution and
+receives the resolved configuration plus a per-load `Validation` context. It can
+collect multiple independent `validate.error` and `validate.warning` reports.
+Warnings continue the lifecycle and are returned on success; any error returns a nil
+result with the full safe diagnostic and source report.
+
+Primary and related paths must be valid for the application schema. Omitted declared
+fields and missing string-map or dynamic keys are valid report targets; unknown
+struct fields and malformed paths produce `validate.invalid_path`. ConfigKit attaches
+the exact surviving input location when one exists, otherwise the nearest input
+container location, or no primary location for defaults-only synthetic state.
+
+Validation is read-only. ConfigKit projects the configuration immediately before and
+after the callback and returns `validate.mutation` at every detected net-change path,
+including nested mutable state. A value that can no longer be projected is also a
+mutation failure. No mutated or otherwise invalid configuration is published.
+Callback panics remain programming failures, and retained contexts use the same
+fixed closed-context panic as version and resolution callbacks.
+
+Only schema-bound exported state participates in loading, resolution audit,
+validation audit, metadata, and snapshots. Ignored or unexported ordinary fields are
+zero in returned detached values. Applications retain responsibility for domain
+rules and runtime initialization; validators should not start clients or depend on
+live services as a substitute for configuration validation.
+
+## Strict document composition
+
+ConfigKit strictly composes parsed base documents when `Options.Imports` is true.
+Application defaults do not participate in this operation.
+
+| Existing node | Incoming node | Result |
+| --- | --- | --- |
+| Absent | Absent | Absent |
+| Absent | Present | Retain the incoming node |
+| Present | Absent | Retain the existing node |
+| Mapping | Mapping | Recurse by mapping key |
+| Any other pair of present nodes | Any other pair of present nodes | `compose.conflict` |
+
+Every non-mapping overlap is a conflict, even when values are equal. Nulls and
+sequences are present atomic values, so they also conflict when repeated; sequences
+are never joined by index. Disjoint entries under shared mappings compose, making
+stable keyed mappings the natural representation for independently contributed
+entries.
+
+An empty mapping contributes no child definitions. Two empty mappings compose, and
+an empty mapping neither clears nor conflicts with another mapping's children.
+Shared mapping containers retain all contributing value locations as their composite
+base origin. A conflict reports the first claim as its primary location and every
+remaining claim as related locations, in deterministic source and declaration
+traversal order. Traversal order never authorizes replacement. Composition clones
+the resulting tree and its ordered claim records rather than mutating or aliasing an
+input document.
+
+## Selected overlays
+
+`Options.Overlay` selects at most one overlay by name. Names must match
+`[a-zA-Z0-9_-]+`; they are not paths. The empty name and exact lowercase name
+`default` select no overlay, and `overlays/default.yml` is never loaded implicitly.
+Every other name resolves only to `<configuration-root>/overlays/<name>.yml`, with
+no extension fallback, case normalization, inheritance, or overlay stack. A selected
+missing overlay is an error.
+
+The overlay is a separately policy-validated YAML mapping. It is loaded after the
+base import graph is composed and its schema version is checked, but before defaults
+and typed decoding. Overlay bytes, nodes, and source records count toward the same
+aggregate limits as base inputs. Its canonical path must remain within the configured
+root and must not duplicate a file already present in the base graph.
+
+Overlay is intentionally distinct from strict composition:
+
+| Existing lower node | Incoming overlay node | Result |
+| --- | --- | --- |
+| Absent | Value | Retain the overlay value |
+| Value | Absent | Retain the lower value |
+| Mapping | Mapping | Recurse by mapping key |
+| Any other pair of present nodes | Any other pair of present nodes | Replace the entire lower node |
+
+Scalars, sequences, and null are atomic. Thus an overlay sequence replaces rather
+than extends a base sequence, `[]` clears it, null is an explicit replacement, and
+cross-kind replacement is allowed when the final application schema accepts it.
+Replacing a subtree removes all displaced descendants from effective presence and
+origin data; history retains the displaced definitions and identifies the parent
+replacement. Surviving overlay paths have overlay origins, while recursively shared
+mapping containers retain their contributing locations.
+
+An overlay may not contain `configkit` anywhere, contribute the configured schema
+version, or replace an ancestor of that version with a scalar or null. These rules
+apply even if the supplied version text would be unchanged. Overlays cannot mask a
+base parse, composition, or version failure because those checks run first.
+
+## Explicit CLI overrides
+
+`Options.Overrides` accepts only records the application knows were explicitly set
+by its CLI parser. Each `Override` supplies a non-root mapping `Path`, a detached
+`Value`, and a required safe display `Flag` such as `--workers`; ConfigKit has no CLI
+parser dependency. Parser defaults must not be submitted as overrides, and `Flag`
+must never contain the raw argument or configured value. General environment
+variable overlays are an explicit non-goal: environment access is reserved for
+typed secret references.
+
+Overrides apply after the selected overlay and before typed defaults/decoding, so
+the input precedence is application defaults < composed base < selected overlay <
+CLI. Recorded resolution, typed secret lookup, and semantic validation follow the
+effective override tree. Overrides also work with `NoSource`.
+
+Values are converted directly into ConfigKit's owned tree without YAML parsing or
+string coercion. Supported values are `nil`, built-in strings and booleans, all
+built-in signed and unsigned integer widths except `uintptr`, finite `float32` and
+`float64`, and recursive `[]any`/`map[string]any`. Strings stay strings; duration and
+secret fields therefore receive string values. Nil is explicit null; empty strings,
+false, and zero remain intentional; empty sequences replace whole lists; and mapping
+values recursively overlay existing mappings. Map keys are sorted canonically and
+sequence order is preserved.
+
+All records are detached and validated before any is applied. Root and explicit
+sequence-index paths are invalid; parsed numeric tokens remain mapping keys. A path
+may create missing mapping ancestors but cannot traverse an existing scalar, null,
+or sequence. Duplicate and ancestor/descendant-overlapping records are rejected.
+Neither paths nor values may create `configkit`, and no record may overlap the
+configured schema-version path. Unknown fields and effective type mismatches remain
+ordinary strict-decoder errors.
+
+At most 1,024 records are accepted, and each record creates one synthetic CLI
+source after file/overlay sources in supplied order. Override sources share the
+1,024-source ceiling. A record has an 8 MiB string-byte limit; override strings and
+source bytes share the 64 MiB aggregate limit. Synthetic mapping keys and values
+count toward the existing 1,000,000-node and depth-256 ceilings. Cycles, named or
+unsupported types, nonfinite floats, and limit excesses fail with safe `override.*`
+diagnostics. Diagnostics and provenance identify the safe `Flag` source, never raw
+arguments or values.
+
+Override origins are explicit CLI origins. History retains replaced base/overlay
+definitions and records equal-value replacements as well as structural changes.
+Caller-owned maps and slices are snapshotted during loading and must not be mutated
+concurrently with the call. The executable `ExampleOverride` shows translating a
+parser's explicit-set state into records while preserving an explicitly supplied
+zero.
+
+## Explicit imports
+
+Imports are opt-in. With `Options.Imports` enabled, a document may reserve its root
+`configkit` mapping for an `imports` sequence. ConfigKit removes that mapping before
+application decoding. Each sequence item is a mapping with exactly one nonempty
+string `path` or `glob` plus an optional boolean `optional`; all other shapes and
+fields are `import.invalid`. A `configkit` key below the root is invalid. With
+imports disabled, any occurrence remains `import.disabled`.
+
+The directive key is `configkit`, not the `_configkit` spelling used in v0.1.0.
+There is no legacy alias: `_configkit` is ordinary application data, subject to
+normal schema validation, and does not trigger imports. When upgrading, rename
+directive keys in root files and imported fragments, and rename any application
+fields previously named `configkit` to avoid the newly reserved key.
+
+Path declarations use slash-separated relative paths. Absolute paths and network
+URLs are invalid. Each path resolves from its declaring file's canonical directory,
+and files are traversed depth-first in declaration order: a file contributes its own
+body before its imports. Order stabilizes source records and diagnostics but never
+permits replacement. Required missing paths fail; `optional: true` suppresses only
+target nonexistence, not invalid paths, containment failures, directories,
+permissions, parse errors, or composition errors.
+
+Glob declarations use the slash-based Go `path.Match` grammar: `*`, `?`, character
+classes, and backslash escapes are supported, while recursive `**` syntax is invalid.
+Backslashes escape pattern characters rather than acting as directory separators.
+ConfigKit validates the complete pattern before filesystem traversal, walks only
+directories selected by preceding segments, and reads wildcard directories in
+bounded batches. Every examined entry consumes the separate visit budget, including
+nonmatches. Matches are sorted lexicographically by slash-relative spelling within
+each declaration before depth-first source traversal. A required zero-match glob is
+`import.missing`; `optional: true` suppresses only zero matches. Invalid patterns,
+walk failures, matched directories, invalid documents, escapes, and repeated targets
+remain errors. Final candidates are bounded by the remaining source limit before
+their contents are accumulated.
+
+The configuration root defaults to a selected file's canonical directory. A file
+source may supply `FilesystemContext.Root` to widen that root but may not supply
+`BaseDir`. Whenever byte and reader sources supply filesystem context, they must
+provide both `BaseDir` and `Root` as absolute existing directories; their diagnostic
+labels, including URI-looking labels, never imply filesystem paths. The base and
+selected file must be inside the canonical root. Nonregular targets are rejected before opening to avoid blocking on FIFOs;
+post-open regular-file checks remain in place under the stable-input assumption.
+ConfigKit canonicalizes symlinks,
+checks containment with relative paths, and opens the canonical root-relative target
+through a library-owned root handle. Contained relative or absolute symlink targets
+are accepted; escapes are rejected. Canonical paths define identity, so hard links at
+distinct paths remain distinct sources.
+
+An active-stack repeat is `import.cycle` and reports the complete cycle's import
+sites. A previously visited canonical path is `import.repeated` and reports both
+inclusion routes, including diamonds and aliases. Each accepted file is read once.
+Imported fragments may contain their own root directives, but may not claim the
+application's schema-version path or replace one of its ancestors; the version must
+come from the selected source. No directory is scanned implicitly, including one
+named `conf.d`, and ConfigKit performs no remote fetching.
+
+## YAML documents
+
+The private YAML boundary currently accepts exactly one nonempty document whose root
+is a mapping. Comments and block or flow collections are supported. It rejects:
+
+- empty input or an empty document;
+- every additional document, including an empty one;
+- duplicate decoded mapping keys;
+- non-string mapping keys;
+- explicit tags, anchors, aliases, and merge keys;
+- a quoted or plain mapping key equal to `<<`; and
+- input exceeding the fixed depth or node limits.
+
+Mapping key comparison is exact: it performs no case folding or Unicode
+normalization. The private document tree retains declaration order, exact validated
+number spelling, source identifiers, and separate key/value line and column
+locations. It contains no upstream parser nodes or types.
+
+Root depth is zero. Input depth is limited to 256 and each parsed input tree to
+1,000,000 nodes, counting mapping keys as input nodes. The upstream parser also has
+a private calibrated depth guard; passing that guard never bypasses ConfigKit's tree
+limits.
+
+## Scalars
+
+Scalar meaning is determined by ConfigKit rather than upstream coercion:
+
+| Input form | Meaning |
+| --- | --- |
+| Quoted, literal, or folded scalar | String |
+| Plain `true` or `false` | Boolean |
+| Plain `null`, `~`, or an empty mapping value | Null |
+| JSON decimal number | Number, retaining its exact spelling |
+| Date/time-looking or other ordinary plain text | String |
+
+JSON numbers permit an optional minus, a zero or nonzero decimal integer without a
+leading zero, an optional fraction with at least one digit, and an optional decimal
+exponent. Hexadecimal, octal, digit separators, leading plus, leading/trailing-dot
+forms, incomplete exponents, and non-finite values are rejected. Legacy boolean
+words (`yes`, `no`, `on`, and `off`) and non-lowercase variants of the reserved
+boolean/null words are rejected unless quoted.
+
+Mapping keys use the same scalar classification and must classify as strings. Quote
+keys that otherwise classify as a boolean, number, or null.
+
+## Application schema binding
+
+ConfigKit builds a private reflection descriptor graph for each schema operation;
+it keeps no global mutable descriptor cache. A configuration root must be a struct
+or string-keyed map. Nested supported shapes are:
+
+- booleans, strings, signed and unsigned integers, and finite floating-point types;
+- `time.Duration`, typed `Secret` references, and paired
+  `encoding.TextMarshaler`/`TextUnmarshaler` scalars;
+- pointers, structs, string-keyed maps, slices, fixed arrays, and `any`; and
+- recursive type definitions whose eventual application values are acyclic.
+
+Named scalar types retain their Go identity. `uintptr`, complex numbers, functions,
+channels, unsafe pointers, non-string map keys, and nonempty interfaces are not
+configuration types. A custom text scalar must provide both directions on its value
+or pointer method set. Building a descriptor only inspects method sets; it never
+executes application methods or parser-specific hooks.
+
+Exported struct fields use an explicit `yaml` name or the lowercase Go field name.
+Unexported fields and `yaml:"-"` are ignored. `omitempty` is accepted but does not
+change binding or projection. An explicit `yaml:",inline"` flattens a struct
+or pointer-to-struct, or designates at most one string-keyed inline map for otherwise
+unmatched names. Ambiguous names, named inline fields, multiple inline maps, and
+unsupported or malformed tag options are schema errors. Inline pointers must
+terminate in a struct; pointer-to-map and recursive pointer-only inline declarations
+are rejected before the defaults factory runs. Embedded fields are ordinary
+named fields unless explicitly inlined. `configkit:"secret"` is the only current
+ConfigKit field tag and marks its bound field or container for secret classification
+and redacted inspection.
+
+Schema path traversal uses these same bindings. Explicit key segments address
+mappings, explicit index segments address sequences, and parsed numeric pointer
+tokens become indices only in a sequence. Sequence indices must use canonical
+nonnegative decimal spelling: no signs or leading zeroes except `0` itself.
+Tokens such as `+0` and `-0` remain literal keys in mappings but do not identify
+sequence elements. Fixed-array indices are bounds checked. Dynamic `any` and inline-map entries
+remain schema-valid for application-defined descendants, but dynamic values cannot
+introduce typed secret references.
+
+Descriptors are reused by typed decoding, projection, and cloning so those operations
+cannot acquire different field bindings.
+
+### Canonical module options
+
+Applications with a known module catalog represent each configured item as an object
+with an explicit module identifier and an options mapping. Ordinary typed structs,
+including a small union of optional option fields, use the same strict binding above;
+application validation decides which fields and combinations apply to each module.
+String shorthand, a library module registry, and custom structural decoder hooks are
+not supported alternatives.
+
+When a runtime-selected catalog genuinely requires dynamic options,
+`map[string]any` retains ConfigKit's canonical dynamic scalars. In particular,
+integers are `int64`; application validation owns allowed keys, value constraints,
+range checks, and conversion to runtime `int` or catalog objects. ConfigKit does not
+provide generic subtree conversion, and consumers must not add a YAML marshal/decode
+round trip to exercise supported behavior. The
+[consumer adoption guide](consumers/README.md) contains compiled typed and dynamic
+examples.
+
+## Defaults and typed decoding
+
+The private decoder starts from an independently owned clone of the application's
+typed defaults and applies only explicitly present input nodes. Defaults therefore
+never become explicit, while equal-valued input remains explicit. Successful decode
+produces detached typed state, baseline and final canonical trees, an input-presence
+index, and default/input origins for the later public loading lifecycle.
+
+| Configured input | Effect on the typed baseline |
+| --- | --- |
+| Absent field | Retain the default |
+| Explicit false, zero, or empty string | Replace the default |
+| Partial mapping or string-keyed map | Recurse and retain omitted default children or entries |
+| Empty mapping | Retain existing mapping children |
+| Sequence, including an empty sequence | Replace the entire sequence |
+| Pointer object | Recurse into a non-nil default; otherwise allocate an object whose omitted children have ordinary Go zero values |
+| Allowed null | Replace the value with nil and suppress its default |
+
+Null is allowed only for pointers, maps, slices, and dynamic `any` values. It is an
+error for scalars, structs, and arrays. New map entries and sequence elements begin
+from their Go zero values; ConfigKit does not invent entry-level defaults.
+
+Decoding is strict at every typed depth. Unknown struct fields, type mismatches,
+invalid nulls, numeric overflow, and arrays with the wrong length are errors at the
+original semantic path and source coordinates. String-keyed maps accept arbitrary
+keys but preserve the strict schema of their values; inline maps accept unmatched
+keys according to their element descriptor. Multiple independent field failures are
+collected without publishing the partially decoded object.
+
+Booleans and strings are not generally coerced. At exactly a configured
+`VersionRule.Path`, strict decimal-integer input may decode into a plain `string`, a
+named string without a text codec, or pointer wrappers around those types. The
+exception is load-local and does not apply to unrelated fields or loads without a
+version rule. Integer destinations require integer syntax
+and a value in the destination type's range. Float destinations accept finite JSON
+numbers representable by their destination precision. Dynamic numbers become
+`int64` for integer syntax and `float64` for fractional or exponent syntax, with
+range and finiteness checks. Named scalar types retain their identity. Durations
+decode only from strings accepted by `time.ParseDuration`; integers are rejected.
+Paired text scalars decode only from strings through `encoding.TextUnmarshaler`, and
+codec failures are classified without exposing application error text or input
+values.
+
+This decoder is available only through `Load`; ConfigKit exposes no generic document
+conversion API.
+
+## Typed projection and ownership
+
+ConfigKit can internally project a schema-valid application value directly into its
+owned canonical tree without YAML serialization. Projection includes every bound
+field, including ordinary zero values; `omitempty` has no effect. Struct fields keep
+binding order, dynamic map keys sort by decoded string, and sequences keep their
+order. Integers retain exact base-10 values, finite floats use their destination
+precision, durations use `time.Duration.String`, and paired text scalars use their
+canonical marshaled text.
+
+Nil pointers, maps, slices, and dynamic values project as null. Non-nil empty maps
+and slices remain empty containers, preserving the distinction. Recursive acyclic
+objects are supported. Cyclic values, non-finite floats, unsupported dynamic concrete
+types, invalid codec output, and depth/node-limit violations fail with safe schema
+classifications that omit codec error text.
+
+The same descriptor graph creates detached typed copies. Pointers, maps, slices,
+arrays, nested dynamic values, and shared references are recursively copied; shared
+pointer identity is not preserved as configuration meaning. Paired text scalars are
+rebuilt by unmarshaling their canonical text into fresh values, detaching private
+backing storage. Ignored and unexported struct fields are zeroed rather than copied.
+
+Private structural comparison operates on canonical trees. Mapping additions,
+removals, and descendant replacements retain semantic paths. A sequence is atomic:
+any sequence change reports the sequence path and never invents correspondence
+between old and new indices. Cross-kind and null/container changes replace the
+affected path.
+
+These mechanisms support decoding, resolution auditing, metadata,
+and rendering. They are not a public generic conversion or cloning API.
+
+## Safe failures
+
+Source failures use stable `source.*` codes and YAML failures use stable `yaml.*`
+codes declared by the root package. Diagnostics contain safe classifications,
+semantic paths when applicable, and available source coordinates. Raw parser,
+conversion, reader-error, and input text is not forwarded. Source labels and
+diagnostic messages are application-visible and therefore must never contain
+secrets; terminal control characters are escaped by `WriteDiagnostics`.

docs/consumers/README.md

@@ -0,0 +1,132 @@
+# Consumer Adoption Guide
+
+ConfigKit removes parser setup, strict decoding, presence bookkeeping, import and
+selected-overlay traversal, precedence, provenance, secret lookup, and safe inspection from
+applications. Consumers still own their configuration structs, defaults, semantic
+validation, schema-version policy, CLI parsing, runtime matching and conversion,
+resource checks, remote acquisition, and service initialization.
+
+The maintained [`examples/consumers`](../../examples/consumers) package demonstrates
+four sanitized shapes using only ConfigKit and the Go standard library:
+
+| Shape | Demonstrated fit | Application code deliberately retained |
+| --- | --- | --- |
+| Narratio-like | Fresh defaults, explicit partial imports, artifact maps, recorded inherited defaults, normalization, and source ownership | Artifact meaning and the separate `model_profile` domain field |
+| Notarius-like | Canonical object bindings, a string-backed schema version accepting string or integer YAML, strict dynamic options, and `int64` dynamic integers | Catalog selection, allowed option keys, range-checked conversion to runtime `int` |
+| WeatherReporter-like | Defaults-only loading, report maps, canonical module objects, typed option unions, explicit CLI records, and typed secret startup | Report/module compatibility, rejection of explicitly empty domain lists, CLI parsing, and startup ordering |
+| Seriatim-like | Independent strict ordered speaker and autocorrect rule files | First-match and ordered replacement algorithms; no central application configuration file |
+
+The YAML under [`testdata`](../../examples/consumers/testdata) is loaded by the
+executable examples and ordinary tests. It contains no private application data,
+credentials, network calls, or dependency on a sibling checkout.
+
+The Notarius-shaped fixtures deliberately load both `version: 4` and
+`version: "4"` into the same string-backed application field. Its version checker
+still owns the supported identifier; fractional numeric input and unsupported
+integer identifiers remain negative examples.
+
+## Happy path
+
+An application defines ordinary types and passes one explicit source. Optional
+features appear only when the application needs them:
+
+```go
+result, err := configkit.Load[Config](configkit.File(path), configkit.Options[Config]{
+    Definition: rules,
+    Imports:    useDeclaredImports,
+    Overlay:    selectedConfigOverlay,
+    Overrides:  explicitlySetFlags,
+})
+if err != nil {
+    return err
+}
+return start(result.Config)
+```
+
+Simple consumers use neither imports nor selected overlays. A complex consumer can opt into
+both without redefining their syntax. ConfigKit overlays are configuration overlays;
+they do not select or replace an application's LLM, model, pipeline, report, or
+execution profile concepts.
+
+Known module catalogs should use canonical object entries with a module identifier
+and typed options. A small union struct is sufficient when the available option
+fields are known; validation selects which fields apply to each module. Runtime-
+selected catalogs may retain `map[string]any`, whose integers are `int64`; applications
+validate keys and ranges and convert only at their runtime boundary. Neither shape
+needs YAML reserialization, a parser hook, a ConfigKit registry, or a generic subtree
+conversion API.
+
+## Source-aware application path policy
+
+[`LoadNotariusPaths`](../../examples/consumers/consumers.go) is the maintained
+path-bearing example. Its application resolver uses `Resolution.InputInfo` and
+`Resolution.Source` before normalizing: relative CLI input uses an explicitly
+supplied invocation directory, retained defaults use the canonical main source,
+and a file-authored scalar uses its one declaring source. Absolute paths remain
+unchanged. Its executable test covers the matching effective YAML and explanation
+history, source-file ownership, and a symlink opened through an alias; canonical
+target-file directories, rather than the alias directory or process working
+directory, are the selected bases.
+
+The selected example policy leaves a relative value unchanged and emits a warning
+when a CLI base is absent or file provenance is missing or composite. That is an
+application choice, not a ConfigKit fallback: consumers can instead reject it or
+choose another explicit base. The example intentionally performs neither target
+existence checks nor confinement checks.
+
+## Intentional migration changes
+
+The examples preserve domain meaning while adopting one configuration convention:
+
+- Explicit empty strings, lists, zeroes, false values, and nulls remain intentional.
+  ConfigKit accepts an empty list structurally; WeatherReporter-shaped validation
+  rejects an explicitly or programmatically supplied empty module/template list as a
+  domain rule. Loaded and constructed values use the same validator.
+- Canonical module and object bindings replace string shorthand. Unknown fields and
+  incompatible option shapes fail at their semantic paths.
+- Schema versions remain string-backed in application types. A configured
+  `VersionRule` accepts string or strict decimal-integer YAML at its exact path and
+  supplies the spelling to both the checker and a plain string destination.
+- Integers inside dynamic options are portable `int64` values. Runtime `int`
+  conversion is explicit and range checked.
+- Strict YAML intentionally rejects duplicate keys, aliases, merge keys, unsupported
+  tags/scalars, trailing documents, and unknown typed fields. Diagnostics expose
+  stable classifications and safe paths, not copied parser text.
+- General environment-variable configuration overlays retire. Application CLI
+  parsers translate only explicitly set configuration flags into `Override` records.
+  Separate invocation state remains outside configuration.
+- Credential fields migrate to environment-name `Secret` references. Applications
+  explicitly call `LoadSecretsDir` before `Load` when they choose file bootstrap;
+  blocked empty variables remain blocked, and ordinary `Load` never changes the
+  process environment.
+
+### Selected-overlay migration
+
+To adopt the current selected-overlay API, rename `Options.Profile`,
+`LayerProfile`, and `CodeProfile*` references to their `Overlay` equivalents; move
+selected files from `profiles/<name>.yml` to `overlays/<name>.yml`; update any
+handling of the `overlay` layer and `overlay.*` diagnostic strings; then rebuild.
+The [configuration contract](../config.md#selected-overlays) is the canonical
+behavioral reference. Application-owned profile concepts, such as `model_profile`,
+are unchanged, and any CLI flag rename remains the application's decision.
+
+These examples are migration evidence, not completed changes to Narratio, Notarius,
+WeatherReporter, or Seriatim. Updating those repositories, their deployed YAML, CLI
+wiring, runtime catalogs, and operational documentation remains separate downstream
+work.
+
+## Maintained API examples
+
+Every nontrivial initial API sketch has a compiled example or a
+focused behavioral owner:
+
+| Roadmap surface | Maintained owner |
+| --- | --- |
+| `Load`, `NoSource`, validation, versions, resolution, `SecretEnv`, overrides, and explanation | Executable examples in [`example_test.go`](../../example_test.go) |
+| Source/import/selected-overlay pipeline rules and artifact defaults | Narratio-shaped executable example and fixture |
+| Canonical module objects and dynamic option handling | WeatherReporter- and Notarius-shaped examples and migration tests |
+| `LoadSecretsDir`, bootstrap reporting, typed lookup, CLI explanation | `Example_weatherStartup` |
+| Results, metadata, diagnostics, effective output, and writer failures | Focused root-package load, provenance, rendering, and explanation tests |
+
+The package-level import-boundary test covers the consumer examples too: supported
+usage names no YAML dependency, parser type, parser option, or parser error chain.

docs/development.md

@@ -1,60 +1,155 @@
 # Development
 
-This is the contributor entry point for ConfigKit. Read the task-specific owners
-below before making changes. The repository is in pre-implementation: it has no
-Go module, packages, tests, or executable examples yet. The
-[component overview](internal/overview.md) owns the implementation inventory.
+Start here when contributing to ConfigKit. Read the task-specific owners below
+before making changes. The [component overview](internal/overview.md) maps
+implementation responsibilities; the [configuration contract](config.md) owns
+public behavior.
 
 ## Initial orientation
 
 1. Inspect the working tree and preserve unrelated changes.
-2. Read the architecture policy for code or design work.
-3. Read the policy, contract, and internal documents applicable to the task.
-4. Inspect relevant implementation and tests where they exist before changing them.
+2. Use the Policy Reading Guide below to select applicable policies.
+3. Read the contract and internal documents applicable to the task.
+4. Inspect the relevant implementation and behavioral tests before changing them.
+
+## Policy Reading Guide
+
+| Policy | Read before… |
+| --- | --- |
+| [Policy set provenance](policy/meta.md) | Adopting policies, checking upstream revisions, or updating the adopted policy set. |
+| [Agents](policy/agents.md) | Recommending, planning, or implementing repository changes. |
+| [Architecture](policy/architecture.md) | Planning or changing Go library code or its structure. |
+| [Testing](policy/testing.md) | Selecting validation for code changes, or adding, changing, removing, or evaluating tests. |
+| [Documentation](policy/documentation.md) | Writing, revising, or reorganizing documentation. |
+| [OSS](policy/oss.md) | Adding or updating dependencies or incorporated third-party material, or changing licensing or attribution. |
+| [Release](policy/release.md) | Preparing or publishing a release, changing release procedures, or making versioning and compatibility decisions. |
+
+- Read applicable policies before making decisions they govern; multiple policies
+  may apply.
+- Select policies using the task triggers above. Follow cross-references to
+  relevant sections when needed to resolve a concrete question.
+- Reuse policies already available in context; reread when changed or no longer
+  available.
+- Expand reading when the task's scope expands.
+- When revising a policy itself, read that policy and any provisions elsewhere
+  affected by the revision.
 
 ## Task-specific reading guide
 
 | Task | Read |
 | --- | --- |
-| Repository orientation or component responsibility | [Architecture policy](policy/architecture.md) and [component overview](internal/overview.md) |
-| Documentation changes | [Documentation policy](policy/documentation.md) and the owning document |
-| Architecture decisions or future work | [Documentation policy](policy/documentation.md), [initial target design](roadmap/initial.md), and relevant ADRs listed below |
-| Code and test changes | [Architecture policy](policy/architecture.md), [testing policy](policy/testing.md), and owning contracts/tests as they are introduced |
-| Examples or copyable assets | The owning implemented contract and related maintained examples, once available |
-| Release preparation | [Release policy](policy/release.md) and [release-readiness gaps](roadmap/release-readiness.md); the operational runbook will be added before release |
+| Repository orientation or component responsibility | [Component overview](internal/overview.md) |
+| Documentation changes | The owning document |
+| Licensing, dependencies, attribution, or release-document changes | [Project grant](../COPYRIGHT) and [attribution](oss/attribution.md); release changes also follow the release procedure |
+| Architecture decisions or future work | [Deferred scope](roadmap/deferred.md) and relevant ADRs listed below |
+| Code and test changes | The owning contract and tests from the map below |
+| Examples or copyable assets | The owning implemented contract and [consumer adoption guide](consumers/README.md) |
+| Release preparation | [Release procedure](release.md) |
 
 Accepted decisions:
 
 - [Separate composition and overlay](adr/0001-separate-composition-and-overlay.md)
 - [Own YAML semantics behind a private parser boundary](adr/0002-own-yaml-semantics.md)
 - [Preserve presence and record application resolution](adr/0003-preserve-presence-and-resolution-history.md)
-
 - [Secret references and explicit bootstrap](adr/0004-secret-references-and-explicit-bootstrap.md)
 - [Explicit overrides and safe explanation](adr/0005-explicit-overrides-and-safe-explanation.md)
+- [Keep the public facade root-owned](adr/0006-public-facade.md)
 
-For cross-cutting changes, follow every applicable row. The
-[implementation plan](roadmap/implementation.md) owns the ordered stages and their
-acceptance checks; all remain pending until implementation evidence is recorded.
+For cross-cutting changes, follow every applicable row. Completed implementation
+and remediation plans are preserved in Git history at `cb5b435`; use current
+contracts and the component overview for ongoing work. For example:
+
+```sh
+git show cb5b435:docs/roadmap/remediation.md
+```
+
+Release-candidate, publication, and verification work follows the operational
+[release procedure](release.md). Its single publication command validates the
+committed candidate and publishes only the intended refs.
+
+The completed string-and-integer schema-version implementation and remediation
+records are preserved in Git history at `244104f`. The
+[configuration contract](config.md#application-schema-versions) owns current behavior.
+
+The completed source-origins and public-facade roadmaps, implementation plan, and
+resolved review findings are preserved in Git history at `5760614`, for example
+`git show 5760614:docs/roadmap/remediation.md`. The earlier source-origins staged
+plan remains at `28e7fc5:docs/roadmap/implementation.md`. Current resolution
+behavior belongs to the [configuration contract](config.md#recorded-application-resolution),
+and current facade ownership belongs to the [component overview](internal/overview.md).
 
 ## Baseline validation
 
-For the current documentation-only repository:
+The completed overlay rename plan and release-workflow simplification record are
+preserved in Git history at `73ce6e9` under `docs/roadmap/`. Current overlay
+behavior belongs to the [configuration contract](config.md#selected-overlays),
+and release operations belong to the [release procedure](release.md).
+
+Install Go 1.25.0 or a supported patched/newer Go toolchain. Acquire declared
+dependencies explicitly before entering an offline development or validation
+environment:
 
 ```sh
-git diff --check
+go mod download
 ```
 
-Also inspect new untracked documents, verify changed local links and heading
-fragments, and review paths, examples, ownership, and current-versus-planned
-claims. The command above does not check links or untracked content.
+Run the everyday check with Bash 3.2 or newer and Git:
 
-Go validation is not runnable until a module and packages exist. The scaffolding
-change must establish and verify library test, vet, and build commands here,
-including their prerequisites. Do not use an application binary build as the
-library baseline. Add executable-example and other checks when those artifacts
-are introduced; do not document nonexistent tools as operational.
+```sh
+./scripts/check.sh
+```
 
-Once code exists, use focused checks while iterating and validation proportionate
-to the change under the testing policy. Documentation-only work does not require
-Go checks unless it changes behavior-bearing examples or commands they validate.
-Release validation is a separate, stricter gate governed by release policy.
+[The script](../scripts/check.sh) runs from the repository root regardless of the
+invocation directory. It checks Go formatting without rewriting files, checks
+staged/unstaged and untracked whitespace, then runs `go test ./...`,
+`go vet ./...`, and `go build ./...`, stopping on the first failure. It uses the
+installed Go toolchain by default, honors an explicit `GOTOOLCHAIN`, and disables
+dependency downloads. Acquire dependencies and any selected toolchain beforehand.
+Format reported Go files with `gofmt -w <files>`.
+
+The default suite includes executable examples, maintained consumer fixtures,
+local documentation-link checks, and the dependency import-boundary check.
+It must stay deterministic and runnable without network access or credentials.
+Still inspect new/untracked content and review paths, examples, ownership, and
+current-versus-planned claims; automated checks do not replace content review.
+
+Use focused checks while iterating, with validation proportionate to the change
+under the testing policy. Documentation-only work normally needs the local-link
+check below and whitespace review; behavior-bearing examples and commands also
+need execution. Use `go test -race ./...` for ownership or concurrency changes.
+The [publication command](release.md#4-publish-the-committed-candidate) invokes
+the release checker once. It performs one minimum-toolchain offline race-suite
+run, one full vet pass, and Linux cross-builds using readonly module mode.
+It already covers examples, links, and package boundaries; do not additionally
+run the everyday checker just to repeat those checks. CI never gates a release.
+
+## Task-to-test map
+
+Commands run from the repository root after dependency acquisition. These are
+starting points for focused iteration; run the everyday check before handing off
+code changes. Use the component overview to find the corresponding implementation.
+
+| Task | Behavioral test owners | Focused command |
+| --- | --- | --- |
+| YAML syntax, diagnostics, parser limits | [Adapter tests](../internal/yaml/parse_test.go), [source translation](../internal/engine/parse_test.go) | `go test ./internal/yaml` and `go test ./internal/engine -run '^TestParseSource'` |
+| File/reader access, imports, globs, containment | [Sources](../internal/engine/source_test.go), [FIFO](../internal/engine/source_fifo_test.go), [imports](../internal/engine/imports_test.go), [globs](../internal/engine/glob_test.go) | `go test ./internal/engine -run 'Source\|Import\|Glob\|Filesystem\|Nonregular\|RegularFile'` |
+| Composition, selected overlays, CLI precedence | [Composition](../internal/engine/compose_test.go), [overlay](../internal/engine/overlay_test.go), [selected overlays](../internal/engine/selected_overlay_test.go), [overrides](../internal/engine/override_test.go) | `go test ./internal/engine -run 'Compose\|Overlay\|Override'` |
+| Schema, defaults, projection, cloning | [Schema](../internal/engine/schema_test.go), [decoding](../internal/engine/decode_test.go), [projection](../internal/engine/projection_test.go) | `go test ./internal/engine -run 'Schema\|Decode\|Projection\|Clone\|Inline\|CompareDocument'` |
+| Lifecycle, resolution, validation, callback ownership | [Loading](../internal/engine/load_test.go), [resolution](../internal/engine/resolution_test.go), [validation](../internal/engine/validation_test.go), [ownership](../internal/engine/callback_ownership_test.go), [independence](../internal/engine/independence_test.go) | `go test ./internal/engine -run 'Load\|Resolution\|Validation\|Validator\|Hook\|Callback\|Parallel'` |
+| Paths, metadata, provenance | [Paths](../internal/engine/path_test.go), [metadata](../internal/engine/metadata_test.go), [provenance](../internal/engine/provenance_test.go) | `go test ./internal/engine -run 'Path\|Metadata\|Provenance\|Queries'` |
+| Secrets, bootstrap, redaction, explanation | [References](../internal/engine/secret_reference_test.go), [bootstrap](../internal/engine/secrets_test.go), [rendering](../internal/engine/render_test.go), [explanation](../internal/engine/explain_test.go) | `go test ./internal/engine -run 'Secret\|Bootstrap\|Effective\|Explain\|Explanation\|History\|Sensitivity'` |
+| Consumer examples and migration fixtures | [Consumer tests](../examples/consumers/consumers_test.go), [API examples](../example_test.go) | `go test ./examples/consumers` and `go test . -run '^Example'` |
+| Documentation links and dependency isolation | [Link checks](../documentation_test.go), [import boundary](../import_boundary_test.go), [public boundary](../public_boundary_test.go) | `go test . -run 'TestLocalDocumentationLinks\|TestDependencyImportBoundary\|TestPublicFacadeBoundary'` |
+| Development and release checker behavior | [Shell regression](../release_check_test.go) | `go test . -run 'TestCheckScripts\|TestDevelopmentCheck'` |
+| Guarded release publication and recovery | [Publication regression](../release_publish_test.go) | `go test . -run '^TestReleasePublication'` |
+
+## Fuzz validation
+
+Run the bounded fuzz targets independently from the repository root. These exact
+commands keep each campaign short and constrain concurrent workers:
+
+```sh
+go test ./internal/engine -run='^$' -fuzz='^FuzzParsePath$' -fuzztime=30s -parallel=2
+go test ./internal/yaml -run='^$' -fuzz='^FuzzParseDocument$' -fuzztime=30s -parallel=2
+go test ./internal/engine -run='^$' -fuzz='^FuzzCompositionAndOverlay$' -fuzztime=30s -parallel=2
+```

docs/internal/extraction.md

@@ -0,0 +1,418 @@
+# Source Extraction Inventory
+
+This inventory records reusable implementation evidence from sibling applications.
+Those checkouts are review inputs only: ConfigKit does not import them, and its
+build and tests must not require them. ConfigKit's current contracts and roadmap
+govern every adaptation.
+
+## Inspected revisions
+
+| Application | Revision | Worktree | Role |
+| --- | --- | --- | --- |
+| Narratio | `b68435128be1e24b94fc7ec259d6e9093669fd99` | Clean `main` tracking `origin/main` | Primary parsing, composition, import, profile, presence, defaults, resolution, and inspection source |
+| WeatherReporter | `5d306a202471e10fe98923a1df27d0b0fce5c666` | Clean `main` tracking `origin/main` | Secrets bootstrap and simple-consumer/defaults/options evidence |
+| Notarius | `77ae132e5609916da40dcd4fcc749c000a63cbac` | Clean `main` tracking `origin/main` | Canonical binding, string-version, and dynamic-option migration evidence |
+| Seriatim | `0fc92f364316c874d366b00cdc884a33e1900b25` | Clean `main` tracking `origin/main` | Independent ordered speaker/autocorrect rule evidence |
+
+These revisions were inspected on 2026-09-06. Paths below are relative to each
+application repository. Record later source revisions and adaptations here when
+the owning implementation work extracts a symbol or case.
+
+## Adaptation rules
+
+- Copy and generalize only the smallest applicable mechanism or behavioral case.
+- Replace upstream YAML nodes, application types, commands, logging, digests, and
+  provider registries with ConfigKit-owned boundaries.
+- Preserve strictness, deterministic behavior, and useful failure coverage while
+  changing expectations that conflict with ConfigKit's accepted contracts.
+- Use sanitized local fixtures only. Audio, transcripts, credentials, private
+  configuration, and whole application package trees are application-only.
+- Record the exact copied/generalized symbols and tests in the owning section when
+  extraction occurs. Assignment prose records the original work boundary; dated
+  implementation records state what was actually generalized.
+
+## Narratio evidence
+
+### Source parsing and strict input
+
+Assigned to the YAML/source implementation:
+
+- Production: `internal/config/load.go` functions `decodeStrictYAML`,
+  `decodeStrictYAMLFromReader`, and `LoadSessionBytesWithOptions`; and
+  `internal/config/composition.go` functions `parseCompositionDocument`,
+  `parseCompositionBytes`, and `buildCompositionNode`.
+- Cases: `TestLoadersRejectTrailingYAMLDocuments`,
+  `TestStrictYAMLRejectsParserExposedEmptyTrailingDocument`, and
+  `TestStrictYAMLAcceptsSingleDocumentAndRejectsUnknownFields` in
+  `internal/config/loader_strict_test.go`; plus duplicate-key, alias, non-mapping,
+  malformed-input, scalar spelling, presence, declaration-order, and source-label
+  coverage in `TestParseCompositionDocumentRetainsPresenceOwnershipAndDeclarationOrder`
+  and `TestParseCompositionDocumentRejectsAmbiguousOrMalformedYAML`.
+- Preserve: labeled reader/byte input, strict unknown-field intent, rejection of
+  trailing documents (including an empty second document), duplicate detection,
+  and source-aware failures.
+- Adapt: translate v4 parser nodes into ConfigKit's private document tree, apply
+  ConfigKit's scalar grammar and limits, and replace raw parser errors with safe
+  diagnostics. Narratio's application decoders and YAML node types are not copied.
+
+Implementation record (2026-09-06): the labeled byte/reader ownership and strict
+single-document cases above were generalized into `source.go`, `parse.go`, and
+`internal/yaml`. No production line was copied verbatim. ConfigKit adds byte and
+tree ceilings, shared atomic reader claims, regular-file checks, exact numeric
+lexemes, parser-depth calibration, ConfigKit-owned locations, safe diagnostic
+codes, and an AST import-boundary regression. Application typed decoding, parser
+errors, YAML node types, and session-specific loaders were not retained.
+
+### Strict composition
+
+Assigned to document composition:
+
+- Production: `mergeAdditiveComposition`, `mergeAdditiveCompositions`,
+  `validateAdditiveClaims`, `appendCompositionClaims`, `mergeAdditiveNodes`,
+  `newCompositionConflict`, and cloning/path/source helpers in
+  `internal/config/composition.go`.
+- Cases: `TestMergeAdditiveCompositionJoinsOnlyDisjointMappings`,
+  `TestMergeAdditiveCompositionRejectsEveryDuplicateClass`, and
+  `TestMergeAdditiveCompositionReportsAllClaimingSources`.
+- Preserve: recursive joining of disjoint mappings, collisions for every overlapping
+  non-mapping value (including equal values and sequences), all claimant sources,
+  deterministic traversal, and nonmutation of inputs.
+- Adapt: empty mappings follow ConfigKit's no-child operation rule; paths use the
+  ConfigKit semantic path model; both precise locations and composite origins are
+  retained. Default values never participate in strict composition.
+
+Implementation record (2026-09-06): `composeDocuments`, its pre-order claim
+collection, conflict construction, and recursive mapping join in `compose.go` adapt
+the assigned production symbols. `TestComposeDocumentsJoinsDisjointMappingsAndTracksClaims`,
+`TestComposeDocumentsRejectsEveryPresentNonMappingOverlap`, and
+`TestComposeDocumentsReportsAllClaimantsAtExactLocations` adapt the assigned cases.
+The intentional empty-mapping difference is covered separately: empty mappings retain
+container provenance but contribute no child claims. No other semantic deviation
+from the extracted additive composer was required.
+
+### Imports
+
+Assigned to explicit import traversal and glob handling:
+
+- Production: `loadPipelineCompositionSources`,
+  `splitPipelineCompositionEnvelope`, `loadPipelineImports`, and related ownership
+  structures in `internal/config/pipeline_composition.go`.
+- Cases: `TestSplitPipelineCompositionEnvelopePreservesInputAndDeclarationOrder`,
+  `TestSplitPipelineCompositionEnvelopeRejectsMalformedShapesWithoutMutation`,
+  `TestLoadPipelineCompositionImportsDisjointFieldsAndTracksOwnership`,
+  `TestLoadPipelineCompositionMergesDisjointKeyedEntries`,
+  `TestLoadPipelineCompositionRejectsBaseConflictsWithAllSources`,
+  `TestLoadPipelineCompositionRejectsUnsafeOrInvalidImports`,
+  `TestLoadPipelineCompositionRejectsSameFileAliasesAndImportedComposition`,
+  `TestLoadPipelineCompositionReportsImportedParseAndSchemaSources`, and
+  `TestLoadPipelineCompositionKeepsRelativePathsRootBased`.
+- Preserve: explicit declarations, declaration-order traversal, disjoint
+  composition, conflict attribution, malformed/unreadable target failures, directive
+  removal, and imported parse/schema source labels.
+- Adapt: replace the root-only `composition` envelope with recursive
+  `_configkit.imports`; add path and glob declarations, bounded depth-first graph
+  traversal, canonical containment, cycle/diamond routes, and fixed source IDs.
+  Canonical paths—not `os.SameFile`—define identity, so hard links remain distinct.
+
+Path-import implementation record (2026-09-06): `splitImportDirectives`,
+`parseImportDeclaration` (now in `directives.go`), `importFilesystem` (now in
+`filesystem.go`), and `importTraversal.visitPath`/`loadImportedDocuments` in
+`imports.go` adapt the assigned envelope, loading, source,
+and failure mechanics. The corresponding ConfigKit tests adapt the assigned
+declaration-order, disjoint composition, keyed-entry, all-source conflict, unsafe
+target, alias, imported parse/schema, and relative-resolution cases. ConfigKit adds
+recursive bounded DFS, `os.OpenRoot` confinement, canonical symlink identity,
+cycle/diamond route locations, optional-path semantics, aggregate budgets, and
+fragment version-placement enforcement. That checkpoint parsed glob syntax behind an
+explicit unsupported gate that the subsequent glob implementation removed; hard
+links intentionally replace Narratio's same-file rejection with path identity.
+
+Glob-import implementation record (2026-09-06): ConfigKit retains the extracted
+declaration order, import failures, composition, and identity cases while adding the
+new `expandImportGlob`, `readGlobMatches`, and pattern-validation mechanisms in
+`glob.go`. Focused cases cover lexical ordering, multiple declarations, overlap,
+directories, hard links, contained and escaping symlinks, unmatched declarations,
+malformed and recursive patterns, escaped metacharacters, character classes,
+permission failures, explicit `conf.d` use, and entry/candidate budgets. This work
+has no Narratio production equivalent; it uses the selected standard-library
+`path.Match` and bounded `File.ReadDir` adaptation rather than its flat loader.
+
+### Upstream profiles and ConfigKit selected overlays
+
+The following upstream symbols and case names retain their original profile
+terminology. ConfigKit adapts their selected-overlay behavior without renaming the
+upstream evidence:
+
+- Production: `mergeOverlayComposition`, `mergeOverlayNodes`,
+  `selectPipelineProfile`, `loadPipelineProfileOverlays`, and
+  `loadedProfileOverlay`.
+- Cases: `TestLoadPipelineProfilesSelectDefaultAndExplicitOverlay`,
+  `TestLoadPipelineProfileSelectionErrors`,
+  `TestPipelineProfileNamesRejectControlCharacters`,
+  `TestLoadPipelineProfilesValidateEveryDeclaredOverlay`,
+  `TestLoadPipelineProfileOverlaySemantics`,
+  `TestLoadPipelineProfileRejectsNullAndKindChanges`, and
+  `TestLoadPipelineProfilePairResolvesIndependentEffectivePipelines`.
+- Preserve: recursive mapping overlay, atomic scalar/sequence replacement,
+  deterministic selection failures, source ownership, and independent results.
+- Adapt: load only the selected fixed overlay path; lowercase `default` means no
+  selection. ConfigKit permits null and cross-kind replacement and does not support
+  declared defaults, inheritance, arbitrary overlay paths, or validating every
+  unselected overlay.
+
+Implementation record (2026-09-06, updated 2026-09-23): `overlayDocuments`,
+`mergeOverlayMappings`, `loadSelectedOverlayDocument`, and
+`overlayDirectiveDiagnostics` adapt the assigned merge, selection, loading, and
+ownership mechanics. `TestOverlayDocumentsRecursesMappingsAndReplacesAtomicSubtrees`,
+`TestLoadAppliesSelectedOverlayAfterBaseAndBeforeDefaults`, selected-overlay
+selection/error, directive/version, containment, and budget cases adapt the assigned
+tests. ConfigKit
+uses exactly one fixed selected `.yml` source, permits null and cross-kind replacement,
+retains displaced descendant history, rejects any overlay directive or version-path
+contribution, and counts the overlay in aggregate budgets. Narratio's declared
+default, multi-overlay validation, inheritance-like application conventions, and
+null/kind restrictions were not retained.
+
+### Effective inspection and provenance
+
+Assigned to layered metadata, redaction, rendering, and explanation:
+
+- Production: `EffectivePipelineValues`, `EffectivePipelineSources`,
+  `MarshalEffectivePipeline`, `effectivePipelineFieldPaths`,
+  `effectivePipelineOwners`, and composition `semanticRecords`/
+  `compactSemanticRecords`.
+- Cases: `TestCompositionCanonicalOutputsAreDeterministic`,
+  `TestEffectivePipelineValuesIgnoreEquivalentSourceLayout`,
+  `TestConfigValidateAndShowPipelineOnlyAreSideEffectFree`,
+  `TestConfigSourcesReportsStableOwnership`,
+  `TestConfigSourcesReportsCanonicalFamilyAndPublishOrigins`,
+  `TestConfigSourcesPreservesProfileOwnershipThroughFamilyExpansion`, and
+  `TestConfigSourcesReportsRootImportProfileAndDefaultOwnership`.
+- Preserve: deterministic effective projection, stable logical paths, source
+  ownership, side-effect-free inspection, and domain-attribution evidence.
+- Adapt: project directly from ConfigKit-owned typed values without YAML round trips;
+  add line/column locations, composite origins, complete operation history, detached
+  records, and redaction. Narratio commands, diff/digest APIs, generated artifact
+  attribution, campaign logic, and party expansion remain application-owned.
+
+Layered-provenance implementation record (2026-09-06): ConfigKit integrated its
+previously extracted source claims, overlay displacement records, typed baseline,
+and audited resolution snapshots in `load_metadata.go`. The representative
+`TestLayeredProvenanceAgreesWithResolvedSnapshot` adapts Narratio's stable ownership,
+profile ownership, deterministic effective projection, and side-effect-free
+inspection cases across one default/import/overlay/resolution workflow. ConfigKit
+adds chronological descendant history for parent and whole-sequence operations,
+composite empty-mapping origins, canonical resolution reasons/dependencies, private
+snapshot agreement, defensive nested copies, and concurrent load isolation. Value
+That checkpoint deliberately left rendering, redaction, explanation, commands,
+generated attribution, diffs, and digests outside its scope.
+
+Effective-rendering implementation record (2026-09-06): ConfigKit adapts Narratio's
+deterministic effective-output and side-effect-free inspection cases in
+`classifySecretPaths`, `redactedDocument`, `Result.WriteEffective`, and the private
+`internal/yaml.Write` adapter. Tests cover stable sorted mappings, preserved sequence
+order, explicit indentation/line/document formatting, tagged containers, dynamic
+current and historical paths, fixed-point dependency cycles, nil/empty distinctions,
+resolved values, text-scalar snapshot reuse, application YAML-hook isolation,
+non-disclosure through failures and record formatting, caller mutation, and writer
+failures. Unlike Narratio's marshal/reparse path, ConfigKit renders only its owned
+frozen tree and substitutes redaction before the upstream dumper boundary. Historical
+value explanation and secret references were implemented at their later owning
+boundaries and are exercised by the consumer startup example below.
+
+### Defaults, presence, and domain resolution
+
+Assigned across schema, decoding, resolution, validation, and consumer examples:
+
+- Production: `NormalizeConfig.UnmarshalYAML`, `outputPathWasSet`,
+  `applyPipelineDefaults` and its component default helpers, `Resolve`,
+  `ResolveLoadedPipelineCampaign`, `mergeCampaignSession`, `selectStableInput`, and
+  application-supplied byte loading in `internal/app/config_loader.go`.
+- Cases: `TestNormalizeLoadAndValidate`,
+  `TestRepresentativeLoadDefaultsAndValidation`,
+  `TestMarshalEffectivePipelineRendersStablePublicConfiguration`,
+  `TestPipelineCampaignRegistryStrictDecode`,
+  `TestCampaignSessionMergeFillsStableInputs`,
+  `TestCampaignSessionMergeSessionOverridesStableInputs`,
+  `TestLoadWithSessionOptionsCarriesExplicitProfilePresence`, and the maintained
+  extraction-example coverage in `TestMaintainedExtractionExamplesPreservePublishedContracts`.
+- Preserve: fresh defaults, explicit-presence-sensitive domain decisions, strict
+  nested types, stable input selection, application-supplied labeled bytes, and
+  validation after resolution.
+- Adapt: presence comes from metadata rather than custom YAML hooks or pointer/zero
+  guesses; explicit empty and null values are retained; defaults are cloned and
+  application-owned; every domain mutation is recorded. Campaign/session fallback,
+  search paths, fetching, storage, and concrete default values remain in Narratio.
+
+Implementation record (2026-09-06): ConfigKit generalized Narratio's fresh-default,
+strict nested-type, and explicit-presence cases into `decode.go` and
+`decode_test.go`. The decoder applies the owned document tree over a detached typed
+baseline, treats mappings recursively and sequences atomically, preserves explicit
+false/zero/empty/null, rejects unknown nested fields, and returns private presence
+and default/input origin artifacts. Unlike Narratio's custom YAML hooks and
+pointer/zero inference, presence comes directly from the parsed tree and equal-valued
+input remains explicit. ConfigKit also adds destination-width numeric checks,
+dynamic `int64`/`float64`, exact arrays, duration strings, paired text codecs, safe
+multi-error collection, and repeated-result isolation. Resolution, validation,
+consumer defaults, and all campaign/session algorithms remain assigned to later
+work.
+
+Lifecycle integration record (2026-09-06): the public single-source `Load` boundary
+combines the already extracted labeled-source and strict-decoding mechanisms with
+Narratio's fresh-default and presence expectations. ConfigKit adds an application-
+defined pre-decode string-version check, defaults-only `NoSource` operation,
+detached base/default metadata and source reports, and explicit gates for every
+later lifecycle option. No application loader or production line was copied.
+Narratio's resolution, validation, import/profile, campaign/session, and command
+behavior remains assigned to its later owning work.
+
+Resolution implementation record (2026-09-06): ConfigKit adapted the intent of
+Narratio's `Resolve`, `applyPipelineDefaults`, component default helpers,
+`mergeCampaignSession`, and `selectStableInput` into a generic recorded resolver in
+`resolution.go`. The synthetic timeout/artifact cases preserve explicit-input
+decisions, derived dependencies, normalization, and map copy/writeback without
+copying campaign/session algorithms or concrete defaults. ConfigKit adds structural
+mutation auditing, container coverage, helper/path consistency checks, equal-value
+intent, coalesced repeated writes, private before/after snapshots, deterministic
+record ordering, and safe hook diagnostics. Semantic validation remains assigned to
+the next lifecycle work.
+
+Validation implementation record (2026-09-06): ConfigKit generalized Narratio's
+`TestNormalizeLoadAndValidate`, `TestRepresentativeLoadDefaultsAndValidation`,
+strict registry decoding, and maintained extraction-example expectations into the
+post-resolution `Validation` lifecycle and synthetic consumer examples. ConfigKit
+keeps domain rules application-owned, resolves schema-valid missing/dynamic report
+paths to nearest input locations, collects independent warnings/errors, and audits
+the full typed projection to reject validator mutation. Live resources, registries,
+campaign/session logic, commands, and application runtime initialization were not
+extracted.
+
+### Secrets bootstrap
+
+Assigned to the explicit bootstrap operation:
+
+- Production: `loadSecretsFromConfigWithDependencies`, `validateSecretDirectory`,
+  `validateSecretFile`, `readAPIKeyFile`, and
+  `internal/fileops/read_bounded.go` function `ReadFileBounded`.
+- Cases: `TestLoadSecretsFromConfigLoadsValidFiles`,
+  `TestLoadSecretsFromConfigPreservesExistingEnv`,
+  `TestLoadSecretsFromConfigRelativeDirUsesCWD`,
+  `TestLoadSecretsFromConfigMissingDirFails`,
+  `TestLoadSecretsFromConfigUnreadableValidEntryFails`,
+  `TestLoadSecretsFromConfigRejectsUnsafeModes`,
+  `TestLoadSecretsFromConfigRejectsNonRegularAndOversizedEntries`, and
+  `TestLoadSecretsFromConfigRejectsSymlinkAndAncestorReplacement`.
+- Preserve: bounded reads, valid environment names, existing variables (including
+  empty values) winning, regular-file checks, symlink rejection, and failure cases.
+- Adapt: use ConfigKit's deterministic report/preflight/apply state machine and
+  fixed budgets. Logging, configuration-driven implicit invocation, private-mode
+  conventions, and application API-key plumbing remain in Narratio.
+
+Implementation record (2026-09-06): `LoadSecretsDir`, `readSecretsEntries`,
+`readSecretValue`, and the private environment/file seams in `secrets.go` adapt
+Narratio's bounded-read and preserve-existing mechanisms at revision
+`b68435128be1e24b94fc7ec259d6e9093669fd99`. The corresponding tests retain its
+valid-file, existing-variable (including empty), missing/permission/read,
+nonregular, symlink, and byte-limit cases. ConfigKit validates invalid entries
+rather than skipping them, permits ordinary deployment permission modes, resolves
+the selected directory symlink, performs complete preflight before mutation, and
+emits per-file safe records without application configuration or logging.
+
+## WeatherReporter evidence
+
+### Secrets bootstrap
+
+Assigned to the explicit bootstrap operation:
+
+- Production: `loadSecrets`, `applySecrets`, `restoreEnvironment`, `secretValue`,
+  and `environmentValue` in `internal/config/secrets.go`.
+- Cases: `TestLoadSecretsDisabledLeavesEnvironmentUnchanged`,
+  `TestLoadSecretsOverwritesExistingEnvironment`,
+  `TestLoadSecretsTrimsOneTrailingLineEnding`,
+  `TestLoadSecretsRejectsInvalidDirectoryEntries`,
+  `TestLoadSecretsRejectsMissingDirectory`,
+  `TestLoadFileSecretDirectoryFailureLeavesEnvironmentUnchanged`,
+  `TestLoadFileValidationFailureLeavesSecretEnvironmentUnset`, and
+  `TestApplySecretsRollsBackOnEnvironmentFailure`.
+- Preserve: separate read/preflight and apply mechanisms, one-newline handling,
+  invalid-name/type/read coverage, no writes after preflight failure, and controlled
+  environment-write failure coverage.
+- Adapt: existing variables—including empty ones—are skipped, never overwritten;
+  application failures produce an accurate partial report and no rollback. Skip
+  entries are not read. Bootstrap is explicitly invoked and remains independent of
+  YAML loading and semantic validation.
+
+Implementation record (2026-09-06): the same `secrets.go` state machine adapts
+WeatherReporter's `loadSecrets`/`applySecrets` separation, environment-name check,
+regular-file rejection, and exact one-LF/CRLF removal at revision
+`5d306a202471e10fe98923a1df27d0b0fce5c666`. Tests adapt its newline matrix,
+invalid-entry and preflight-no-write cases, and controlled application failure.
+The overwrite/rollback expectation is intentionally replaced by existing-winner,
+presence-recheck, and partial-progress statuses; no configuration loader invokes
+the bootstrap.
+
+### Defaults, explicit presence, and module options
+
+Assigned to consumer-shaped examples and migration checks:
+
+- Production: `Load`, `mergeFile`, `normalizeReportModules`,
+  `traverseReportModules`, `normalizeModuleOptions`, and `decodeKnownOptions`.
+- Cases: `TestDefaults`, `TestOutputDirectoryLoading`,
+  `TestOutputDirectoryValidationIsConsistentForLoadedAndConstructedConfigs`,
+  `TestLoadMinimalExampleConfig`,
+  `TestReportDistributorPathTemplatesSetTracksExplicitEmptyList`,
+  `TestValidateReportModuleKeysWithoutMutatingOptions`,
+  `TestReportModuleOverridesNormalizesConstructedOptionsWithoutMutatingConfig`,
+  `TestReportModuleOverridesCanonicalizesTypedPointerOptions`,
+  `TestReportDistributorPathOverridesConsistentForLoadedAndConstructedConfig`,
+  `TestReportModuleValidationConsistentForLoadedAndConstructedConfig`,
+  `TestConstructedReportOverridesUseExportedFields`, and
+  `TestConstructedExplicitEmptyReportOverridesAreRejected`.
+- Preserve: defaults-only use, consistent loaded/constructed outcomes, explicit
+  empty-list domain rejection, typed module-specific options, normalization without
+  mutating caller input, and unknown-field rejection.
+- Adapt: ConfigKit permits empty lists structurally and exposes their presence to
+  application validation. Object bindings replace shorthand, explicitly set flags
+  become CLI override records, and general environment overlays retire. Report
+  semantics, registries, rendering, and module option validation remain application
+  responsibilities.
+
+Consumer-example implementation record (2026-09-06): at Narratio revision
+`b68435128be1e24b94fc7ec259d6e9093669fd99`, the maintained consumer cases adapt
+`TestMaintainedExtractionExamplesPreservePublishedContracts`,
+`TestConfigValidateAndShowPipelineOnlyAreSideEffectFree`, and the stable source-
+ownership tests into a sanitized partial-import/artifact fixture. ConfigKit replaces
+application composition envelopes and command output with `_configkit.imports`,
+typed defaults, recorded resolution, metadata, and explanation. Artifact meaning,
+model/pipeline profiles, commands, and generated-domain attribution remain in the
+example application layer; no production function was copied.
+
+At WeatherReporter revision `5d306a202471e10fe98923a1df27d0b0fce5c666`,
+`TestDefaults`, explicit-empty-list cases, loaded/constructed consistency cases, and
+nonmutating module-option normalization were adapted into the WeatherReporter-shaped
+fixtures and tests in [`examples/consumers`](../../examples/consumers). ConfigKit's
+detached defaults replace source mutation, canonical module objects replace string
+shorthand, ordinary validation retains empty-list and option compatibility rules,
+and explicit `Override` records replace external configuration-field overlays. The
+startup example composes the separately implemented bootstrap report, typed secret
+lookup, and explanation APIs without copying WeatherReporter's registries or
+rendering/runtime modules.
+
+Notarius revision `77ae132e5609916da40dcd4fcc749c000a63cbac` supplied
+binding/version/dynamic-option migration evidence only. The local example uses an
+ordinary canonical object, a string `VersionRule`, ConfigKit's `int64` dynamic
+integer convention, and application range checking; it does not copy a catalog or
+environment overlay. Seriatim revision
+`0fc92f364316c874d366b00cdc884a33e1900b25` supplied ordered rule-file evidence.
+The local examples load speaker and autocorrect files independently and keep their
+matching/replacement algorithms outside ConfigKit. Neither source is a build or test
+dependency.
+
+## Application-only material
+
+Do not extract application commands, filesystem discovery, logging, runtime
+initialization, remote clients, LLM/provider setup, audio/transcript fixtures,
+configuration digests, report rendering, campaign/session algorithms, or consumer
+resource validation into ConfigKit. Maintained consumer examples use only small
+synthetic types and fixtures to prove that these responsibilities remain
+straightforward.

docs/internal/overview.md

@@ -1,10 +1,39 @@
 # Internal Component Overview
 
-ConfigKit has no implemented Go packages or components yet. This document will
-inventory components and link to their current contracts and focused internal
-documentation as they are introduced.
+ConfigKit exposes one supported root `configkit` package. The root owns public
+named types, declaration comments, constructors, and explicit conversion/wrapper
+code. It delegates loading and frozen inspection to `internal/engine` through
+private state; public signatures and fields do not expose engine types.
 
-The [architecture policy](../policy/architecture.md) owns binding boundaries and
-invariants. The [initial target design](../roadmap/initial.md) describes planned
-behavior; it is not an inventory of implemented features. See the
-[development guide](../development.md) for contributor orientation and validation.
+Implemented component owners:
+
+- `internal/engine` owns source acquisition, composition, schema inspection,
+  decoding, lifecycle coordination, callback auditing, provenance/history,
+  secret resolution and bootstrap, and safe inspection rendering. It never
+  imports the root package.
+- Root `Source`, `Path`, `Secret`, records, lifecycle callbacks, results, and
+  bootstrap reports are root-defined wrappers or records. Callback wrappers pass
+  only live engine context during a callback; `Result.Config` is detached and its
+  private inspection remains frozen independently.
+- Root conversion files explicitly cross the path, record, callback, secret, and
+  error boundaries. There are no public aliases, anonymous engine embeddings, or
+  public engine bridge methods.
+- `internal/document` owns the parser-independent ordered tree and cloning.
+  `internal/yaml` is the sole upstream YAML adapter and parser/dumper boundary.
+- Engine mechanism tests own source, composition, decoding, callback, provenance,
+  secret, history, rendering, and bootstrap behavior. Root tests own public API
+  compatibility, facade integration, documentation links, and dependency/public
+  boundary checks. Consumer examples remain under `examples/consumers`.
+
+Dependency direction is root to engine to document/YAML support. The root may
+import only `internal/engine` among project internal production packages; engine
+and its supporting packages do not import root. The root boundary test enforces
+these constraints and rejects exported aliases, fields, or signatures involving
+internal types.
+
+The [configuration contract](../config.md) owns implemented YAML and lifecycle
+semantics. The [consumer adoption guide](../consumers/README.md) owns application
+guidance. The [architecture policy](../policy/architecture.md) owns contributor
+boundaries, and [ADR 0006](../adr/0006-public-facade.md) records the facade
+decision. See the [development guide](../development.md) for validation commands
+and [release procedure](../release.md) for source-candidate gates.

docs/oss/attribution.md

@@ -0,0 +1,38 @@
+# Open Source Attribution Notices
+
+## Standard Repository Policies
+
+Material: `docs/policy/meta.md`, `docs/policy/oss.md`,
+`docs/policy/documentation.md`, `docs/policy/agents.md`,
+`docs/policy/architecture.md`, `docs/policy/testing.md`, and
+`docs/policy/release.md`; root `AGENTS.md`; and the Policy Reading Guide in
+`docs/development.md`, adapted for this repository.
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: CC-BY-SA-4.0
+
+License and notices: [CC BY-SA 4.0](licenses/CC-BY-SA-4.0.txt) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/LICENSE).
+
+[Source](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843).
+
+## go-yaml v4
+
+Selected module: `go.yaml.in/yaml/v4` at `v4.0.0-rc.6`.
+
+Copyright 2011-2019 Canonical Ltd
+
+Copyright 2025 The go-yaml Project Contributors
+
+Copyright 2006-2010 Kirill Simonov
+
+SPDX-License-Identifier: Apache-2.0 AND MIT
+
+License and notices: [Apache 2.0](licenses/Apache-2.0.txt) |
+[MIT](licenses/MIT.txt) |
+[NOTICE](https://github.com/yaml/go-yaml/blob/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125/NOTICE) |
+[LICENSE](https://github.com/yaml/go-yaml/blob/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125/LICENSE).
+
+[Source](https://github.com/yaml/go-yaml/tree/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125).

docs/oss/licenses/Apache-2.0.txt

@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
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+
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+
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+      and distribution as defined by Sections 1 through 9 of this document.
+
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+
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+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
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+
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+
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+   limitations under the License.

docs/oss/licenses/CC-BY-SA-4.0.txt

@@ -0,0 +1,170 @@
+Creative Commons Attribution-ShareAlike 4.0 International
+
+ Creative Commons Corporation (“Creative Commons”) is not a law firm and does not provide legal services or legal advice. Distribution of Creative Commons public licenses does not create a lawyer-client or other relationship. Creative Commons makes its licenses and related information available on an “as-is” basis. Creative Commons gives no warranties regarding its licenses, any material licensed under their terms and conditions, or any related information. Creative Commons disclaims all liability for damages resulting from their use to the fullest extent possible.
+
+Using Creative Commons Public Licenses
+
+Creative Commons public licenses provide a standard set of terms and conditions that creators and other rights holders may use to share original works of authorship and other material subject to copyright and certain other rights specified in the public license below. The following considerations are for informational purposes only, are not exhaustive, and do not form part of our licenses.
+
+Considerations for licensors: Our public licenses are intended for use by those authorized to give the public permission to use material in ways otherwise restricted by copyright and certain other rights. Our licenses are irrevocable. Licensors should read and understand the terms and conditions of the license they choose before applying it. Licensors should also secure all rights necessary before applying our licenses so that the public can reuse the material as expected. Licensors should clearly mark any material not subject to the license. This includes other CC-licensed material, or material used under an exception or limitation to copyright. More considerations for licensors.
+
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+
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+
+Creative Commons Attribution-ShareAlike 4.0 International Public License
+
+By exercising the Licensed Rights (defined below), You accept and agree to be bound by the terms and conditions of this Creative Commons Attribution-ShareAlike 4.0 International Public License ("Public License"). To the extent this Public License may be interpreted as a contract, You are granted the Licensed Rights in consideration of Your acceptance of these terms and conditions, and the Licensor grants You such rights in consideration of benefits the Licensor receives from making the Licensed Material available under these terms and conditions.
+
+Section 1 – Definitions.
+
+     a.	Adapted Material means material subject to Copyright and Similar Rights that is derived from or based upon the Licensed Material and in which the Licensed Material is translated, altered, arranged, transformed, or otherwise modified in a manner requiring permission under the Copyright and Similar Rights held by the Licensor. For purposes of this Public License, where the Licensed Material is a musical work, performance, or sound recording, Adapted Material is always produced where the Licensed Material is synched in timed relation with a moving image.
+
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+
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+
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+
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+
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+
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+
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+
+Section 2 – Scope.
+
+     a.	License grant.
+
+          1. Subject to the terms and conditions of this Public License, the Licensor hereby grants You a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to exercise the Licensed Rights in the Licensed Material to:
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+
+               B. produce, reproduce, and Share Adapted Material.
+
+          2. Exceptions and Limitations. For the avoidance of doubt, where Exceptions and Limitations apply to Your use, this Public License does not apply, and You do not need to comply with its terms and conditions.
+
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+
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+
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+
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+
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+
+          1. Moral rights, such as the right of integrity, are not licensed under this Public License, nor are publicity, privacy, and/or other similar personality rights; however, to the extent possible, the Licensor waives and/or agrees not to assert any such rights held by the Licensor to the limited extent necessary to allow You to exercise the Licensed Rights, but not otherwise.
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+
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+
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+
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+
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+
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+
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+
+     b.	ShareAlike.In addition to the conditions in Section 3(a), if You Share Adapted Material You produce, the following conditions also apply.
+
+          1. The Adapter’s License You apply must be a Creative Commons license with the same License Elements, this version or later, or a BY-SA Compatible License.
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+
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+
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+
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+
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+For the avoidance of doubt, this Section 4 supplements and does not replace Your obligations under this Public License where the Licensed Rights include other Copyright and Similar Rights.
+
+Section 5 – Disclaimer of Warranties and Limitation of Liability.
+
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+
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+
+Section 6 – Term and Termination.
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+
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+
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+
+          2. upon express reinstatement by the Licensor.
+
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+
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+
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+
+Section 7 – Other Terms and Conditions.
+
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+
+     b.	Any arrangements, understandings, or agreements regarding the Licensed Material not stated herein are separate from and independent of the terms and conditions of this Public License.
+
+Section 8 – Interpretation.
+
+     a.	For the avoidance of doubt, this Public License does not, and shall not be interpreted to, reduce, limit, restrict, or impose conditions on any use of the Licensed Material that could lawfully be made without permission under this Public License.
+
+     b.	To the extent possible, if any provision of this Public License is deemed unenforceable, it shall be automatically reformed to the minimum extent necessary to make it enforceable. If the provision cannot be reformed, it shall be severed from this Public License without affecting the enforceability of the remaining terms and conditions.
+
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+
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+
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+
+Creative Commons may be contacted at creativecommons.org.

docs/oss/licenses/MIT.txt

@@ -0,0 +1,18 @@
+MIT License
+
+Copyright (c) <year> <copyright holders>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+associated documentation files (the "Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
+following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial
+portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
+LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
+EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+USE OR OTHER DEALINGS IN THE SOFTWARE.

docs/policy/agents.md

@@ -0,0 +1,91 @@
+# Agent Policy
+
+**Base Policy Version:** 1.3
+
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/agents.md)
+
+## Purpose
+
+Agents must read and follow these rules.
+
+## Implementation Discipline
+
+**KEY PRINCIPLES:** Write the simplest idiomatic code that satisfies the user's
+request. Do not implicitly strengthen requirements, restrictions, or guarantees
+beyond what the user actually requested.
+
+**Keep implementation machinery proportionate.** Use straightforward,
+idiomatic code and introduce only the machinery needed to support the requested
+behavior and flexibility. Optimize for conceptual simplicity and
+maintainability, not for the fewest lines, fewest options, or narrowest product
+surface.
+
+**Do not invent restrictions.** Do not reject, prohibit, constrain, cap,
+harden, or otherwise narrow behavior unless required by the user, an explicit
+repository contract, or an unavoidable correctness constraint. Preserve
+operator and caller choice where policy has not been established. If an
+additional restriction appears advisable, present it as a decision rather than
+silently implementing it.
+
+A correctness constraint must follow from the requested behavior or an
+established invariant, not from the convenience of the chosen implementation.
+Explain the specific failure it prevents and why a less restrictive
+implementation cannot satisfy the contract.
+
+**Do not invent guarantees.** Do not strengthen public contracts, guarantees,
+or invariants beyond those expressly requested by the user.
+
+**Use the standard library.** For example: in almost every case, the best
+approach to copying files is to use the standard library. Writing custom code to
+implement power-loss protection at the application level, or to guard against
+bad actors with privileged and concurrent access to the host's filesystem,
+is wasteful, unnecessary, and not idiomatic. Stick to the simple, standard, and
+idiomatic approach unless another path is expressly requested by the user.
+
+**An implementation detail is not repository policy.** Tests and documentation
+must not elevate incidental behavior into a durable guarantee or restriction
+unless that behavior was expressly selected as part of the contract. Existing
+explicit contracts remain authoritative; changing or weakening one requires a
+deliberate decision rather than being inferred from this principle.
+
+Agent-authored plans, tests, documentation, and prior implementations are not
+evidence that an additional restriction was deliberately approved. Identify the
+authorizing requirement or decision; when that authority is unclear, surface
+the ambiguity rather than treating repetition as approval.
+
+## Git Commit Policy
+
+By default, commit each completed, nonempty unit of work using a
+concise, plain-English message describing what changed. This policy is standing
+authorization to create those local commits; a separate user request is not
+required. An explicit user instruction to leave work uncommitted takes precedence.
+
+A unit of work is a focused, reviewable outcome, including its relevant tests and
+documentation.
+Complete the appropriate validation before committing. If work is incomplete or
+validation is blocked, report that state accurately.
+
+Before committing:
+
+1. Run `git status --short` and review the relevant diff, including any staged
+   changes. Identify changes that predate the current unit of work.
+2. Exclude secrets, local environment files, generated junk, and unrelated changes.
+3. Stage only the files or hunks belonging to the completed unit. Use `git add .`
+   only when every included change belongs to that unit. Preserve unrelated
+   staged and unstaged work.
+4. Review `git diff --staged` and run appropriate checks for the change. Reuse
+   successful checks for unchanged content.
+5. Review `git log --oneline -n 10` and use
+   `git commit -m "<concise plain-English commit message>"`.
+6. Report the commit identifier and any remaining uncommitted work.
+
+If the unit cannot be safely separated from pre-existing work, leave it uncommitted
+and explain the overlap rather than silently including that work. If a commit
+fails, preserve the changes and report the failure; do not bypass hooks.
+
+Default commit authorization does not authorize pushing, publishing, amending,
+resetting, reverting, or rewriting history. Those actions require a separate user
+instruction. Do not use `git commit -a` or `git commit --no-verify` to bypass the
+staging and validation discipline above.

docs/policy/architecture.md

@@ -1,18 +1,38 @@
 # Architecture Policy
 
-**Base Policy Version:** 1.0
+**Base Policy Version:** 1.3
 
-**Last Updated:** 2026-09-06
+**Last Updated**: 2026-09-28
 
-## Purpose and applicability
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/architecture.md)
+
+## Purpose And Ownership
+
+The adopted policy defines the application's purpose and the architectural
+constraints contributors must follow. It owns system boundaries, responsibility
+and dependency rules, established invariants, and explicit non-goals.
+
+Describe the concrete package inventory and implementation mechanics in internal
+documentation. Link to canonical public contracts for their exact behavior and
+to ADRs for decision rationale.
 
 ConfigKit is an opinionated Go library for consistent YAML configuration loading
-and resolution across consuming applications. This policy governs contributions
-now; it does not claim that the target features are implemented. The
-[component overview](../internal/overview.md) owns implementation inventory and
-[initial roadmap](../roadmap/initial.md) owns unimplemented target behavior.
+and resolution across consuming applications. The [component overview](../internal/overview.md)
+owns implementation inventory, the [configuration contract](../config.md) owns
+implemented behavior, and the [deferred scope](../roadmap/deferred.md) preserves
+deferred scope.
 
-## Success criteria
+## Adopted Constraints And Implemented Structure
+
+Architectural constraints govern current and future development. Record
+implemented structure accurately, proposals and implementation status in the
+roadmap, and significant decisions and rationale in ADRs. Describe a target
+structure as implemented when its changes land.
+
+Constraints must reflect deliberately selected requirements and decisions.
+Do not promote incidental implementation choices into architectural invariants.
+
+## Success Criteria
 
 1. **Reduce application infrastructure:** Can applications delete substantial
    configuration infrastructure while retaining clear ownership of their domain
@@ -48,10 +68,10 @@ existing primitives cannot accommodate it cleanly, and show how the extension
 preserves a coherent model. Application-specific interpretation and validation
 remain appropriate. Reuse Narratio's applicable infrastructure under these
 boundaries, and keep simple consumers independent of optional composition
-features. The [consumer API design](../roadmap/initial.md#consumer-api-design)
-describes the proposed surface; this policy does not claim it is implemented.
+features. The [consumer adoption guide](../consumers/README.md) demonstrates the
+implemented surface against representative simple and complex shapes.
 
-## Responsibility boundaries
+## Responsibility Boundaries
 
 ConfigKit owns configuration input processing and the coordination of decoding,
 resolution, validation, and inspection. Applications own their configuration
@@ -68,21 +88,33 @@ must never run implicitly as part of configuration loading.
 Remote data can enter through application-supplied input without introducing a
 network provider into the library.
 
-## Public API and dependency direction
+## Public API And Dependency Direction
 
 Keep one small, coherent public surface for the supported lifecycle. Simple
-single-document consumers must not need import, profile, or provider machinery.
+single-document consumers must not need import, overlay, or provider machinery.
 Do not expose parser-specific nodes, errors, or extension hooks through the
 public API. Parser integration belongs behind a private boundary, as recorded
 in [ADR 0002](../adr/0002-own-yaml-semantics.md).
 
+The root `configkit` package is the sole supported consumer import path. Public
+named types stay root-owned and may hold private delegated implementation state;
+their exported signatures, fields, and method sets must not expose internal
+types or acquire internal methods through anonymous embedding. Root production
+code may depend inward on a cohesive engine and its supporting internal packages,
+but internal production packages must not import the root. Explicit forwarding
+and local conversion are acceptable where they preserve type identity,
+ownership, callback lifetime, and inspection behavior. The accepted root-wrapper
+boundary and its migration rationale are recorded in
+[ADR 0006](../adr/0006-public-facade.md); the implemented layout is described in
+the [component overview](../internal/overview.md).
+
 Separate input access, document processing, composition, decoding, metadata, and
 rendering responsibilities without prescribing an interface or package for each.
 Dependencies must preserve those boundaries; package splits and abstractions
 must earn their complexity. Do not impose a full application or hexagonal
 framework on this library.
 
-## Configuration integrity
+## Configuration Integrity
 
 Composition and intentional overlay are distinct operations. Composition must
 not silently become last-wins override through file ordering. The decision and
@@ -94,7 +126,7 @@ same inputs and options. Invalid input must not produce a successful usable
 configuration. Do not run application hooks on invalid typed configuration.
 
 User-controlled precedence is application defaults, composed base, selected
-profile, then explicitly supplied CLI overrides. Applications own flag parsing;
+overlay, then explicitly supplied CLI overrides. Applications own flag parsing;
 ConfigKit owns overlay semantics and provenance. Domain resolution follows these
 inputs and must remain recorded, not become a hidden override channel.
 
@@ -103,14 +135,14 @@ decoding. Preserve presence and source information through processing. Ordinary
 values must not be used to infer whether input was absent. Final configuration,
 metadata, and effective inspection must agree, including application resolution
 changes; see [ADR 0003](../adr/0003-preserve-presence-and-resolution-history.md).
-Safe historical values and an explanation renderer belong to the initial target,
+Safe historical values and an explanation renderer are part of the implemented contract,
 including superseded/deleted paths and effective source attribution. Inspection
 must agree with the final typed snapshot and apply historical sensitivity rules.
 See [ADR 0005](../adr/0005-explicit-overrides-and-safe-explanation.md).
-Detailed syntax and operation tables belong to the target roadmap until their
-current configuration contract is implemented.
+Detailed syntax and operation tables belong to the
+[current configuration contract](../config.md).
 
-## Ownership and confidentiality
+## Ownership And Confidentiality
 
 Returned configuration and metadata must not share mutable state across loads.
 ConfigKit must not mutate a result after returning it. Ordinary exported Go
@@ -131,11 +163,12 @@ forwarded blindly when they can include raw input. Do not log configuration
 implicitly. Applications remain responsible for classifying their secrets and
 for safe messages supplied by their hooks.
 
-## Scope boundaries
+## Scope Boundaries
 
 Do not introduce automatic directory discovery, network providers, arbitrary
 merge strategies, additional configuration languages, or application runtime
 management without concrete consumer evidence and an explicit design decision.
-The roadmap owns the complete deferred-feature inventory. Significant boundary
+The [deferred scope](../roadmap/deferred.md#explicit-non-goals-and-deferred-scope)
+owns the deferred-feature inventory. Significant boundary
 changes require an ADR and corresponding policy/contract updates; implementation
 convenience alone is not a reason to broaden the public API.

docs/policy/documentation.md

@@ -1,126 +1,176 @@
 # Documentation Policy
 
-**Base Policy Version:** 1.0
+**Base Policy Version:** 1.11
 
-**Last Updated:** 2026-09-06
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/documentation.md)
 
 ## Purpose
 
-Assign each documentation topic one canonical owner so ConfigKit's documentation
-remains accurate and useful to consumers, maintainers, and implementation agents.
+This policy assigns each documentation topic to one canonical owner. Its goal is
+to keep ConfigKit's documentation accurate, concise, discoverable, and resistant
+to drift for consumers, maintainers, developers, and coding agents.
 
-## Core rules
+## Core Rules
 
-### One canonical owner
+### One Canonical Owner
 
-Each authoritative fact belongs in one owning document or Go declaration's
-reference documentation. Other documents may summarize and link to that owner;
-they must not maintain competing definitions of commands, API contracts, YAML
-semantics, defaults, paths, diagnostics, or compatibility guarantees.
+Each authoritative fact belongs in one document. A non-owning document may give
+a short, stable summary for orientation, but it must link to the canonical owner
+for volatile details.
 
-### Policies, current behavior, and future work
+Volatile details include commands, flags, configuration fields and defaults,
+module keys, schemas, file names, paths, status codes, retry behavior, and
+runtime guarantees. If readers could reasonably treat a statement as a
+contract, maintain it only in the owning document.
 
-- Policies state currently binding contributor rules, including constraints on
-  future implementation. They do not imply that features already exist.
-- Current API/configuration contracts, consumer guidance, and component
-  documentation describe implemented behavior only, including partial boundaries.
-- ADRs record accepted decisions and rationale. Acceptance is not evidence of
-  implementation; execution status belongs in roadmaps.
-- Roadmaps own unimplemented targets, deferred work, and execution status.
+### Current And Future Behavior
 
-The initial target and implementation plan have separate owners. Do not put
-staged steps or progress in `docs/roadmap/initial.md`. `docs/roadmap/implementation.md` owns those details.
-As behavior lands, move its normative definition into the current contract and
-replace the roadmap definition with a link. Retire completed roadmap material
-as part of release preparation; ADRs preserve significant decision history.
+Outside `docs/roadmap/`, documentation describes implemented behavior only.
+Partial features may be described only to their implemented boundary.
 
-### Audience and examples
+Architectural constraints may govern future changes. Describe current structure
+from implemented behavior.
 
-Consumer documentation explains how to use the library and what consumers own.
-Internal documents explain mechanisms and dependencies. Keep implementation
-mechanics out of consumer guidance unless they affect a meaningful choice.
+ADRs may record an accepted architectural decision before implementation. The
+roadmap owns implementation status and sequencing until the decision is
+implemented. Current architecture, user, operator, integration, and internal
+documentation are updated when the behavior lands.
 
-Complete copyable artifacts belong in `examples/`; Go API examples may live in
-executable Go example tests beside the relevant package. Prose should use the
-smallest useful excerpt and link to the maintained artifact. Examples must be
-secret-free and checked against implemented behavior. Clearly label illustrative
-future syntax in roadmaps; do not present it as a runnable current example.
+`docs/roadmap/deferred.md` owns deliberate exclusions; task-specific plans
+own execution order and progress. Completed plans retire during release
+preparation.
 
-### Security and privacy
+### Audience And Detail
 
-Do not include real credentials, private keys, environment dumps, sensitive input,
-or private infrastructure details unless intentionally public. Document secret
-handling, not secret values.
+Write for the document's stated audience and include only the detail needed for
+its owned topic. Keep user and operator docs focused on using and operating the
+application. Developer docs should link to user-facing and external contracts
+for their definitions.
 
-## Canonical ownership
+### Examples
 
-| Topic | Owner | Boundary |
-| --- | --- | --- |
-| Product orientation | `README.md` | Current status, purpose, navigation, and a minimal working example once available |
-| Contributor entry point | `docs/development.md` | Reading guide and actual baseline validation commands |
-| Architecture rules | `docs/policy/architecture.md` | Responsibilities, dependency constraints, invariants, and scope boundaries |
-| Documentation rules | `docs/policy/documentation.md` | Ownership and document lifecycle |
-| Testing rules | `docs/policy/testing.md` | Risk-based sufficiency, test boundaries, and maintenance principles |
-| Release rules | `docs/policy/release.md` | Compatibility, integrity, gates, immutability, and exceptions |
-| Release procedure | `docs/release.md`, when operational | Exact maintainer commands, prerequisites, supported targets, and verification |
-| Exported Go API | Go documentation beside declarations | Symbol contracts, errors, ownership, and lifecycle API behavior |
-| YAML and resolution semantics | `docs/config.md`, as behavior lands | Syntax, composition, precedence, conversion, secret references/bootstrap, and explanation semantics; Go reference docs link here for shared rules |
-| Consumer walkthroughs | `docs/consumers/`, when useful | Task-oriented usage and consumer responsibilities, not duplicate API reference |
-| Component inventory | `docs/internal/overview.md` | Implemented components and links to their owners |
-| Component mechanics | Other `docs/internal/` files, when needed | Detailed implementation behavior and change recipes |
-| Architectural decisions | `docs/adr/` | Context, decisions, alternatives, consequences, and supersession history |
-| Initial target | `docs/roadmap/initial.md` | Unimplemented end-state and deferred feature scope |
-| Implementation plan | `docs/roadmap/implementation.md` | Stages, dependencies, acceptance gates, and progress |
-| Release readiness gaps | `docs/roadmap/release-readiness.md` | Outstanding release prerequisites and closure evidence |
-| Historical release notes | `docs/releases/` | Version-specific historical summaries required by release policy |
-| Complete examples | `examples/` and executable Go examples | Maintained artifacts; prose links instead of duplicating full examples |
+Complete copyable files belong in `examples/`. Documentation may use the
+smallest illustrative snippet needed to explain its owned topic, but should link
+to maintained examples for complete copyable files.
 
-A listed future owner is not a requirement to create an empty file now. Create
-API, consumer, example, and component documents when the corresponding behavior
-exists and there is useful content to own. Link only to existing files; use plain
-code paths for planned files. Release prerequisites have the explicit temporary
-exception recorded in the release policy.
+Executable Go API examples may live beside the relevant package.
 
-ConfigKit has no owned HTTP service, application CLI, or runtime operations
-interface. Do not create those reference documents for consuming applications.
+Examples must be valid, secret-free, and tested where practical. Commands and
+configuration used in documentation should match the application.
 
-## Boundary rules
+### Security And Privacy
 
-Architecture owns governing constraints; ADRs explain why; contracts describe
-implemented semantics; internal documentation explains how. A roadmap may link
-to all of them but must not become a second current reference.
+Documentation and examples must not contain real credentials, private keys,
+private environment dumps, sensitive source material, or private infrastructure
+details unless intentionally public. Document secret-handling mechanisms, not
+secret values.
 
-Release policy owns guarantees; the release procedure owns commands. A release
-note cannot redefine a compatibility contract or replace a current-documentation
-update. The note at an immutable tag is that release's historical record.
+## Canonical Ownership
 
-This policy owns what documentation may disclose. Architecture owns security
-invariants. Current configuration and Go API contracts own secret-classification
-and rendering behavior when implemented; internal docs own their mechanisms.
+| Topic | Canonical owner | Owned content | Content owned elsewhere |
+| --- | --- | --- | --- |
+| Product orientation and minimal example | `README.md` | Purpose, current status, shortest useful Go example, and navigation, including licensing and attribution. | Full Go API and configuration contracts, release procedure, and implementation detail. |
+| Contributor entry point | `docs/development.md` | Task-oriented reading guide, contributor orientation, baseline validation commands, and canonical links. | Package inventory, architecture rules, subsystem behavior, detailed change recipes. |
+| Application architecture policy | `docs/policy/architecture.md` | System shape, normative ownership, dependency direction, boundaries, invariants, safety properties, and non-goals. | Concrete package inventory, implementation mechanics, contributor procedures, decision history, future work. |
+| Policy-set provenance and upstream navigation | `docs/policy/meta.md` | Policy-set origin, local authority, adoption baselines, and upstream adoption and update links. | Task-specific reading triggers, detailed adoption procedures, and formal attribution notices. |
+| Agent policy | `docs/policy/agents.md` | Proportionate, idiomatic implementation; rules against inventing requirements, restrictions, guarantees, or policy. | Application contracts, architecture, testing policy, and contributor procedures. |
+| Documentation policy | `docs/policy/documentation.md` | Documentation ownership, audience boundaries, maintenance rules, and ADR/document lifecycle. | Application architecture or product behavior. |
+| Testing policy | `docs/policy/testing.md` | Test philosophy, risk sufficiency, boundaries, doubles, coverage, regressions, and test maintenance. | Subsystem behavior, application contracts, subsystem-specific test inventories, and implementation plans. |
+| Release policy | `docs/policy/release.md` | Versioning, compatibility, release integrity and immutability, release documentation, proportionate gates, publication controls, completion, and required versus optional checks. | Repository-specific commands, product installation guidance, CLI version semantics, historical release summaries, and CI implementation detail. |
+| Open source licensing and attribution policy | `docs/policy/oss.md` | License defaults and author choices, COPYRIGHT and attribution formats, license/notice links, discoverability, maintenance, and concrete exceptions. | Component entries, license texts, release commands, and dependency security review. |
+| Project copyright and license grant | `COPYRIGHT` | Project identity, copyright holders and years, SPDX expression, code grant, separately licensed document scope, warranty disclaimer, and third-party statement. | Complete license texts and upstream component attribution. |
+| Project license texts | `LICENSE` | Complete project and incorporated companion license texts, with required project-specific fields. | General licensing policy and upstream component attribution. |
+| Upstream component attribution | `docs/oss/attribution.md` | House Format entries for dependencies and adapted documents: identity, material scope, copyright, license, notices, and source links. | General policy, exception reasoning, and complete standard license texts. |
+| Standard license texts | `docs/oss/licenses/` | Complete, verbatim standard license texts shared by applicable entries, including copied documentation. | Project-specific upstream notices, attribution prose, and policy interpretation. |
+| Repository-specific release procedure | `docs/release.md` | Maintainer prerequisites, candidate preparation, validation and publication commands and automated guards, asynchronous deliverables, delivery status, optional consumer verification, and recovery. | General release requirements, product installation guidance, historical release summaries, and current compatibility contracts. |
+| Exported Go API | Go documentation beside declarations | Symbol contracts, errors, ownership, and lifecycle behavior. | Shared YAML semantics and complete examples. |
+| Configuration contract | `docs/config.md` | YAML syntax, composition, precedence, schema, defaults, resolution, validation, secrets, and explanation semantics. | Go symbol contracts, complete examples, and implementation detail. |
+| Consumer guidance for the public Go API | `docs/consumers/` | Task-oriented public Go API usage, minimal examples, and consumer responsibilities. | Go symbol contracts, configuration semantics, and internal implementation detail. |
+| Inventory of implemented internal packages | `docs/internal/overview.md` | Implemented packages and components, responsibilities, and links to focused internal docs. | Normative architecture, contributor reading policy, external contracts. |
+| Behavior and architecture of internal packages | Other files under `docs/internal/` | Implementation flow, collaborators, state transitions, package-local guarantees and failures, and relevant tests. | Global architecture invariants, configuration definitions and defaults, external schemas, operator procedures. |
+| Architectural decision records | `docs/adr/` | Significant decisions, context, alternatives, rationale, consequences, and supersession history. | Current behavior reference, implementation status, task sequencing. |
+| Deferred scope | `docs/roadmap/deferred.md` | Deliberate exclusions and conditions for reconsideration. | Task execution and current behavior. |
+| Future implementation plans | Task-specific files under `docs/roadmap/` | Unfinished work, sequencing, acceptance, and progress; completed plans retire during release preparation. | Implemented behavior and ADR rationale. |
+| Release-note history | `docs/releases/` | One checked-in summary per source release under the procedure; the note at its immutable tag is the release record. | Current commands, behavior, contracts, and compatibility definitions. |
+| Complete examples | `examples/` and executable Go examples | Maintained copyable artifacts and Go API examples. | Configuration reference, symbol contracts, and prose explanation. |
 
-## Architectural decision records
+Create supporting documents for existing interfaces and responsibilities when
+substantive content is available.
 
-Use sequential filenames, such as `0001-separate-composition-and-overlay.md`,
-and the lightweight Nygard structure: title, status, date, context, decision,
-alternatives considered, and consequences.
+Do not create empty owners.
 
-Accepted decision content is immutable. A changed decision requires a new ADR
-and a superseded status/link in the old one. Navigation links may be repaired
-when specification ownership moves without rewriting historical rationale.
-Rejected architectural alternatives belong in ADRs; deferred or rejected product
-features belong in roadmaps. Do not create an ADR for every routine choice.
+## Boundary Rules
 
-## Maintenance and verification
+### Orientation
 
-Update the owning current documentation in the same change that implements or
-changes behavior. When ownership moves, remove the old definition and preserve
-useful navigation links.
+Link among orientation, architecture, and internal documents; maintain each
+package or behavior description in its canonical owner.
+
+### Go API And Configuration
+
+Go declaration documentation owns exported symbol behavior. The configuration
+contract owns shared YAML and resolution semantics. Consumer guidance explains
+tasks and links to those contracts.
+
+### Releases
+
+The release policy defines requirements and invariants that every release must
+satisfy. The repository-specific release procedure defines the commands and
+workflow maintainers use to satisfy that policy. Release notes record history
+at immutable tags. Maintain current behavior in its canonical documentation,
+update it with the corresponding behavior changes, and keep release procedures
+consistent with adopted policy.
+
+### Project Licensing And Upstream Attribution
+
+README and release documents link to the canonical licensing and attribution
+materials under the [OSS policy](oss.md). The release procedure owns URL
+construction and publication mechanics.
+
+### Contracts And Implementation
+
+Go API and configuration documents define externally observable behavior.
+Internal documents explain implementation and link to the owning contract.
+
+### Security Topics
+
+This policy owns what documentation and examples may contain. Architecture owns
+application security invariants. The configuration and public API contracts own
+secret-classification, bootstrap, and rendering behavior. Internal docs own
+implementation mechanisms only.
+
+## Architecture Decision Records
+
+Use sequentially numbered ADR filenames such as
+`0001-record-architecture-decisions.md`. Follow the lightweight Nygard format:
+
+1. title;
+2. status;
+3. date;
+4. context;
+5. decision;
+6. alternatives considered;
+7. consequences.
+
+Treat the decision content of an accepted ADR as immutable. When a decision
+changes, create a new ADR and update the earlier ADR's status to superseded.
+Rejected architectural alternatives belong in the ADR; rejected product ideas
+belong in the roadmap. Routine choices need no ADR.
+
+## Maintenance
+
+When behavior changes, update its canonical owner in the same change. If
+ownership moves, remove the old definition and replace it with a link where
+navigation remains useful.
 
 Before completing documentation work:
 
-- verify claims against the implementation or clearly identify future design;
-- check changed local links, paths, fragments, examples, and commands;
-- preserve the distinction between policy, decisions, target behavior, and status;
-- check canonical ownership and remove stale or duplicate definitions;
-- inspect formatting and whitespace;
-- ensure no sensitive data was introduced.
+- verify affected behavior and examples;
+- check commands, flags, fields, defaults, schemas, and paths against their
+  implementation;
+- keep unimplemented behavior in the roadmap, subject to the ADR exception;
+- remove stale references and validate links;
+- confirm that non-owning documents summarize and link rather than redefine;
+- confirm that no secrets or sensitive private data were added.

docs/policy/meta.md

@@ -0,0 +1,27 @@
+# Policy Set Provenance
+
+**Base Policy Version:** 1.0
+
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/meta.md)
+
+## Origin And Local Authority
+
+This repository's policy set is adapted from
+[Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy).
+The adopted local policies govern work in this repository. Upstream revisions
+become local policy through deliberate adoption, preserving local decisions.
+Each policy's `Upstream Source` identifies its adopted baseline.
+
+## Adoption And Updates
+
+For policy adoption, upstream revision reviews, and updates, consult the
+[upstream adoption and update guide](https://gitea.maximumdirect.net/eric/policy/src/branch/main/docs/adoption.md).
+That guide and the reference example collection are maintained upstream and
+accessed through links. Keep discovery links pointed at the current upstream
+project and guide; keep adopted-source and example links pinned to commits.
+
+The local [developer guide](../development.md) routes tasks to applicable
+policies. Formal credit and licensing notices for the copied policy material
+belong in the local [attribution document](../oss/attribution.md).

docs/policy/oss.md

@@ -0,0 +1,217 @@
+# Open Source Licensing And Attribution Policy
+
+**Base Policy Version:** 1.8
+
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/oss.md)
+
+## ConfigKit Applicability
+
+ConfigKit's selected grant is LGPL-3.0-or-later, recorded in
+[COPYRIGHT](../../COPYRIGHT), with the complete LGPLv3 and incorporated GPLv3
+texts in [LICENSE](../../LICENSE). The [release procedure](../release.md)
+owns source-only Go module publication through Gitea. No separate hosted release
+object or license asset is required for this channel.
+
+## Purpose And Scope
+
+This policy defines project licensing conventions and a repeatable House Format
+for upstream attribution and license notices. It covers the project's own code
+and upstream components incorporated into or distributed with the application
+or library, including relevant transitive dependencies and copied code,
+documentation, or assets.
+Determine treatment from the component's terms and actual use.
+
+Consulting development guidance or using tooling alone does not require an
+attribution entry. Copying or adapting documentation for inclusion in the
+repository is different: preserve its applicable attribution and license terms.
+A material's role as development guidance does not exempt copied documents.
+Apply any express permissions for attribution-free reuse of example formatting.
+
+The baseline is a publicly available source repository with releases published
+alongside it. The format is independent of language, forge, and build system.
+It does not require attribution for every development tool, establish license
+compatibility, or resolve every obligation arising from use or distribution.
+
+## Canonical Locations
+
+The [documentation policy](documentation.md) assigns ownership:
+
+- `COPYRIGHT`: project name, copyright statements, SPDX expression, grant,
+  warranty disclaimer, and third-party statement.
+- `LICENSE` contains the complete, unmodified project license text, including
+  incorporated companion text. Dependency attribution does not relicense the project.
+- `docs/oss/attribution.md`: canonical component entries.
+- `docs/oss/licenses/`: complete, verbatim standard and applicable companion texts.
+
+Use recognizable license filenames, such as `Apache-2.0.txt` or `LGPL-3.0.txt`.
+A shared standard text may serve multiple entries. Keep explanations outside
+license texts and preserve distinct versions and exceptions.
+
+## Upstream Reference Examples
+
+Use the commit-pinned upstream examples to create actual project notices.
+Retain their links and keep the example collection upstream; keep applicable
+license texts locally as specified above. The
+[standard license-text collection](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/oss/licenses/README.md)
+identifies the available reference texts.
+
+## Project Licensing
+
+Unless the author specifies otherwise, use **GPL version 3 or later**
+(`GPL-3.0-or-later`) for applications and **LGPL version 3 or later**
+(`LGPL-3.0-or-later`) for libraries. An author's explicit choice takes precedence:
+for example, a one-off script may use MIT. Such a choice requires no exception
+rationale, additional approval, or compensating controls under this policy.
+
+These defaults guide new license selection. Adopting this policy does not
+relicense existing code or override third-party terms. Preserve an existing
+license unless the author deliberately changes it. For mixed-purpose projects,
+follow the author's selected scope rather than inferring different licenses for
+individual packages.
+
+Use the upstream [application COPYRIGHT example](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/examples/licensing/application/COPYRIGHT)
+or [library COPYRIGHT example](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/examples/licensing/library/COPYRIGHT)
+to create the project’s root `COPYRIGHT` file.
+Use verified project names, contribution years, and copyright holders.
+For another selected license, adapt the grant, SPDX expression, disclaimer, and
+text references together to reflect the author's selected grant.
+
+For GPLv3 projects, copy the complete GPLv3 text into `LICENSE`. For LGPLv3
+projects, place the complete LGPLv3 text followed by the complete GPLv3 text in
+`LICENSE`; the LGPL incorporates the GPL terms. Keep the texts unmodified and
+place project-specific statements in `COPYRIGHT`. For the default grants, the
+grant and SPDX expression in `COPYRIGHT` must expressly identify `or-later`;
+follow the author’s choice if a different grant is selected.
+
+For other licenses, provide their complete text and any required project-specific
+fields; the standard reference collection remains unchanged. Keep `COPYRIGHT`,
+`LICENSE`, SPDX expressions, and README descriptions consistent with the actual
+grant. This convention introduces no blanket requirement for per-file headers;
+preserve notices or add them where the applicable terms require them.
+
+Identify separately licensed documentation or assets in the project grant, with
+links to their attribution and license information. An application's default
+code license does not override the terms of incorporated documentation.
+
+## Upstream Attribution House Format
+
+Begin `docs/oss/attribution.md` with `# Open Source Attribution Notices`,
+followed directly by component entries. These comprise the complete document.
+
+Each entry presents these five fields in order, with blank lines between them:
+
+1. **Project name** as a level-two heading. An optional identification paragraph
+   may follow, such as `Selected module: MODULE at VERSION.` with the module and
+   version in backticks. For copied documentation, a concise `Material:` sentence
+   may identify the affected files and whether they were adapted or copied
+   without modification. A factual qualifier such as `(transitive dependency)`
+   is permitted. Limit optional identification prose to factual component and
+   material scope.
+2. **Upstream copyright statement or statements**, preserving their wording.
+   Put multiple statements in separate paragraphs. Include this field when the
+   selected upstream source supplies an applicable statement; otherwise, omit it.
+3. **SPDX license identifier or expression**, when applicable, using
+   `SPDX-License-Identifier: EXPRESSION`.
+4. **License and notice links**, beginning `License and notices:`, separated
+   by ` | `, and ending with a period. Label local standard texts by license
+   name, such as `MIT` or `Apache 2.0`. Label upstream files by their actual
+   filenames, such as `COPYRIGHT`, `LICENSE`, `NOTICE`, or `PATENTS`.
+5. **Source repository link**, rendered exactly as `[Source](COMMIT_URL).`.
+
+Use the upstream [attribution example](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/examples/licensing/attribution.md)
+to create the project’s `docs/oss/attribution.md`.
+The example illustrates omitted fields and multiple copyrights and licenses.
+Replace the uppercase placeholders and illustrative URLs with actual component
+information. Local license links are relative to the destination
+`docs/oss/attribution.md`; copy the applicable texts into its `licenses/`
+directory. Do not copy example entries for components the project does not use.
+
+These are five fields, not a line limit. Omit the SPDX field when no applicable
+identifier exists; identify nonstandard terms through the linked text. Preserve
+licensing alternatives and exceptions, and record a selected option when
+relevant through the factual license identification. Do not invent an identifier
+or silently resolve an unsettled licensing choice.
+
+Keep entries factual. Do not add agent-authored explanations of license
+expressions, file-level license scope, research performed, retained source
+notices, or compliance conclusions. Avoid filler such as "none is invented
+here" and embellished link labels such as "upstream LICENSE", "additional
+patent grant", or "at the imported commit". Preserve actual required upstream
+content; this rule excludes editorial additions, not required notices. Policy
+interpretation and exception reasoning belong in the adopted OSS policy or an
+appropriate decision record, not the attribution document.
+
+## License Texts And Upstream Links
+
+Link standard license texts to their local copies. Link project-specific
+notices to their upstream copies. Every upstream repository or notice link must
+identify the exact commit corresponding to the
+imported version, including the selected source revision for copied material.
+
+Classify material according to its contents. An upstream `LICENSE`,
+`COPYING`, or similar file may contain project-specific notices or exceptions
+in addition to standard wording. Link both the local standard text and the
+commit-specific upstream file when needed. Make companion license texts directly
+reachable from the entry.
+
+For project-specific license and attribution material, this policy accepts
+direct links to the applicable upstream texts as satisfying reproduction,
+inclusion, or copy requirements. This is the adopted house interpretation.
+Agents must apply it without adding local-copy requirements or seeking repeated
+approval solely because a license uses those terms.
+
+This interpretation concerns notice reproduction. Concrete obligations such as
+marking modified files or supplying corresponding source receive their own
+applicable treatment. Preserve required notices already present in incorporated
+source files; the central attribution entry does not authorize stripping them.
+
+## Discoverability
+
+End the project's README with two friendly statements linking to its actual
+grant in `COPYRIGHT` and the attribution document. ConfigKit's
+[README](../../README.md) contains the two required statements: one linking to
+the project grant and one linking to attribution.
+
+Each new checked-in release document and its hosted download page must end
+with links whose visible text is `COPYRIGHT | LICENSE | ATTRIBUTION`. Use absolute
+URLs to those files at the release's immutable tag or corresponding immutable source
+revision so the links work in both locations. This release navigation is distinct
+from upstream component links, which must use the imported commit.
+
+Reuse the checked-in release document as the hosted release body where supported.
+The release procedure owns concrete URLs and publication mechanics for delivering
+the links through the selected channel. Do not maintain duplicate notice lists.
+These conventions do not by themselves require separate downloadable license
+assets, source bundles, or a different binary package format.
+
+## Maintenance And Exceptions
+
+Update project licensing statements together when the author changes the grant
+or its scope. Update upstream notices in the change that adds, removes, upgrades,
+copies, or changes the distribution of a relevant component. Check the selected source's license
+and notices rather than assuming they are unchanged. Update affected entries,
+commit links, and texts; retain historical versions through Git.
+
+Check affected statements, faithful standard-text copies, and link destinations
+as part of ordinary change review. For a future release tag, check intended file
+paths against the candidate source; the tag need not resolve remotely before
+publication. Do not add publication-time network checks, CI polling, recurring
+legal sign-offs, mandatory scanners, or a full software bill of materials merely
+to implement this policy.
+
+Use the House Format routinely. Raise an exception only for a concrete obligation
+or unresolved rights question it does not address, including any arising from a
+particular distribution channel. Record the issue and selected treatment in the
+adopted OSS policy or an appropriate decision record. Attribution entries
+contain the resulting factual identification and required material, without
+repeating that reasoning. Resolve the issue before the affected use or
+distribution without reopening settled choices.
+Common ownership of projects is neither required nor a blanket exception.
+
+Apply the formatting convention prospectively. Do not rewrite published tags,
+notes, binaries, or checksums to retrofit it. Address actual omissions deliberately
+under the applicable terms and the [release correction policy](release.md#immutability-and-correction).
+Ordinary attribution maintenance and release links are preparation work, not new
+release approval gates.

docs/policy/release.md

@@ -1,73 +1,97 @@
 # Release Policy
 
-**Base Policy Version:** 0.1.0
+**Base Policy Version:** 1.4
 
-**Last Updated:** 2026-09-06
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/release.md)
 
 ## Purpose
 
-This policy defines the minimum requirements for selecting, validating,
-publishing, verifying, and correcting releases. Its goal is to make every
-release intentional, reproducible from an exact source revision, documented
-for consumers, and safe from retrospective replacement.
+This policy defines a proportionate workflow for validating and publishing an
+intended source revision under a fresh version. Releases should require little
+routine intervention, avoid repeated work, and preserve published contents.
 
-The repository-specific commands that implement these requirements belong in
-`docs/release.md`. Historical release summaries belong in `docs/releases/`.
-Neither document may weaken this policy.
+The repository-specific commands belong in `docs/release.md`. Historical release
+summaries belong in `docs/releases/`. The procedure must agree with the adopted
+policy and link to it rather than introduce additional release requirements.
 
-## ConfigKit applicability
+## ConfigKit Applicability
 
-ConfigKit adopts a source-only Go module release model. The source tag and
-version-matched release note are the declared deliverables. Standalone binaries,
-container images, and separate binary/package-registry publication are not
-required. This does not waive source compilation, module hygiene, testing, or
-consumer-facing module retrieval and build verification.
+ConfigKit publishes a source-only Go module. Its declared deliverables are the
+immutable annotated source tag and version-matched checked-in release note.
+Standalone binaries, container images, hosted release objects, and separate
+registry publication are not required. Additional channels require a deliberate
+update to the policy and procedure.
 
-The release procedure must define the module path, authoritative remote,
-supported Go versions and operating-system/architecture targets, prerequisite
-dependency acquisition, and the exact verification commands once established.
-The default tests themselves remain deterministic and offline. Additional
-publication channels require documented deliverables and verification before use.
-
-The Go API, documented YAML/resolution semantics, and structured diagnostic
-contracts all participate in compatibility review. A signature-preserving change
+The Go API, documented YAML and resolution semantics, and structured diagnostic
+contracts participate in compatibility review. A signature-preserving change
 can still break consumers. Human diagnostic wording is stable only where a
-contract expressly promises it. Minimum Go version and platform support changes
-also require an explicit compatibility assessment.
+contract expressly promises it. Minimum Go version and platform support
+changes also require an explicit compatibility assessment.
 
-## Release Model
+### Platform Support
 
-A release consists of:
+Linux is the release-validated platform. macOS has best-effort support: keeping
+it working remains desirable, but neither native macOS validation nor Darwin
+cross-builds are release gates. Missing macOS evidence or a macOS-specific failure
+does not by itself block a release. Voluntary checks and fixes are welcome; there
+is no guarantee that each release has been validated on macOS.
 
-- one exact source commit reachable from the repository's primary branch;
-- one immutable version tag identifying that commit;
-- one version-matched, checked-in release note; and
-- every artifact, image, package, registry entry, or other deliverable the
-  repository declares for that release.
+The [release procedure](../release.md#release-identity-and-support) owns target
+architectures and required Linux checks. Historical release notes and their
+validation records remain unchanged.
 
-The repository's primary branch is `main` unless an adopted policy documents
-an exception. A release candidate must be committed and pushed to that branch
-before its release tag is published.
+## Release Model And Completion
 
-The source tag is the authoritative release identity. Published deliverables
-must be traceable to the tagged source and must agree with its version. A
-repository may publish source only. When it publishes additional deliverables,
-its release procedure must enumerate them and define how each is built,
-identified, published, and verified.
+A source release identifies one exact committed source revision through an
+immutable version tag and a version-matched, checked-in release note. The
+primary release branch is `main` unless the adopted policy specifies otherwise.
+The procedure must name the authoritative publication remote.
 
-Release automation may validate or publish a release only when its exact
-responsibility is documented. Automation must not silently change the source
-candidate, move a published tag, replace a published deliverable, or repair a
-release in place.
+A successful push of the intended tag, with its source commit available on the
+authoritative primary branch, completes the release. The source commit may be
+pushed before the tag or published together with it through an atomic push.
+The procedure must choose and document the supported approach.
+
+ConfigKit uses sequential explicit pushes: first the captured candidate to
+authoritative `main`, then the annotated tag. Its
+[release procedure](../release.md) names `origin` and checks that its fetch and
+push destinations resolve to the authoritative URL.
+
+Release commands must finish at successful publication. They must not wait for
+or poll CI, require successful CI status, inspect downloadable artifacts, or
+check consumer installation or Go module availability as completion gates.
+A failed or ambiguous push requires resolving the authoritative remote state
+before declaring success or retrying; successful pushes do not require a
+separate remote read-back gate.
+
+Remote tag read-back and fresh consumer retrieval are optional and non-gating
+after successful publication. A failed push receives one bounded check of the
+authoritative ref; do not poll or blindly retry.
+
+Repositories may publish source only. Additional binaries, images, packages,
+checksums, or other declared deliverables may be published asynchronously from
+the tagged source. The procedure must identify those deliverables and the
+responsibility of their automation. Published deliverables must be traceable
+to that source and identify the same version.
+
+ConfigKit currently declares no additional deliverables. Its source-tag push
+is the completion point.
 
 ## Versioning And Compatibility
 
 Stable releases use Semantic Versioning in the form `vMAJOR.MINOR.PATCH`, with
-no leading zeroes. Each version must be unused locally and in every configured
-remote or publication channel before publication begins.
+no leading zeroes. Prereleases require an explicit adopted policy defining
+their format and use.
 
-Unless an adopted policy explicitly supports and defines prereleases,
-prerelease versions are not permitted.
+ConfigKit does not support prereleases.
+
+The selected version must be unused locally and on the authoritative remote.
+Do not require queries to every configured remote or publication service.
+A version known to have already been published must not be reused, even if the
+normal guards do not inspect that channel. Adding a distribution channel
+requires a deliberate update to the policy and procedure where needed.
 
 For releases at or after `v1.0.0`:
 
@@ -80,159 +104,173 @@ configuration, data, integration, or compatibility contract when the release
 note explains the impact and required consumer action. A patch release must
 not intentionally break those contracts within its minor line.
 
-A repository with additional compatibility promises must define them in its
-adopted policy or canonical contract documentation. A release note may explain
-a compatibility change, but it must not redefine the current compatibility
-contract.
+Additional compatibility promises and deliberate exceptions belong in the
+adopted policy or canonical contract documentation. Release notes explain
+changes; they do not redefine current compatibility contracts.
 
-## Release Documentation
+## Release Documentation And Preparation
 
-Every release made under this policy must include
-`docs/releases/<version>.md` in the tagged source tree. The filename must use
-the complete version tag, and the document must begin with a title containing
-the product name and that exact version.
+Every new release must include `docs/releases/<version>.md` in the tagged
+source tree. Use the complete version tag as the filename and begin with a
+title containing the product name and that exact version.
 
-Every new release note must contain these sections:
+ConfigKit requires the first line `# ConfigKit <version>`.
 
-```markdown
-# <Product> vMAJOR.MINOR.PATCH
+Include a short summary and any relevant compatibility impact or upgrade
+instructions. Choose sections suited to the release and keep the note
+proportionate to the change.
 
-This release ...
+Keep exact current contracts in their canonical documents and update affected
+documentation with the behavior change. Link to those documents from the note
+where useful. If annotated tags are used, derive their summary from the
+checked-in note.
 
-## Summary
+ConfigKit uses the complete checked-in note as the annotated tag message.
 
-## Compatibility
+Include the release footer defined by the [OSS policy](oss.md#discoverability)
+in each new release document. The release procedure defines the concrete URLs
+and publication mechanics. Prepare these links with the release note; they do
+not add a network check or approval gate. If a hosted download page is used in
+a future channel, preserve the footer there.
 
-## Upgrade
+Handle version selection, release-note content, and retirement of completed
+roadmaps during preparation. Preserve planned and deferred work and repair
+affected links when retiring roadmaps. Reuse ordinary change review for
+unintended files, credentials, and private data. Scope release-content review
+to the tagged source.
 
-## Changes
-```
+## Candidate Validation
 
-Use an explicit statement such as "No action required" when a section has no
-substantive content.
+Provide one publication command that validates the final committed candidate,
+checks publication state, and publishes the intended refs. A validation-only
+mode or command may be provided for diagnosis, but must not be a required step
+before publication repeats the same checks.
 
-Release notes are immutable historical summaries. They should link to current
-canonical documentation for exact behavior. Every affected canonical document
-must be updated in the same candidate; a release note must not substitute for
-current documentation or defer required documentation changes.
+ConfigKit uses `./scripts/release.sh vMAJOR.MINOR.PATCH`. The separate
+`scripts/release-check.sh` remains an optional diagnostic command; the
+publication command invokes it once and does not use a persistent candidate
+record.
 
-## Candidate Preparation And Validation
+Run the complete deterministic, offline default test suite once for the final
+candidate, following the [testing policy](testing.md). For repositories that
+publish builds, verify the required build targets. Select those targets for
+the application's actual support commitments; native testing on each platform
+and access to particular hardware are not default release prerequisites.
 
-Each repository must provide one documented release-check command or script
-that exercises the complete set of automated source-candidate gates. The
-repository-specific procedure must state all additional manual gates.
+ConfigKit's one maintained Go 1.25 baseline runs the full suite with the race
+detector and test-time vet disabled. This protects library behavior, ownership,
+and concurrent use; the suite already includes examples, consumer fixtures,
+documentation links, and package boundaries. One full vet pass adds static
+checks beyond the test-time subset. CGO-disabled Linux amd64 and arm64 builds
+cover supported configurations distinct from native race compilation. macOS
+and newer-toolchain checks are optional.
 
-The required gates are:
+Additional gates must address a concrete risk that the existing checks do not
+adequately cover. Do not automatically require linting, race testing, module
+hygiene audits, documentation audits, credential scans, example validation, or
+expanded platform matrices solely because they are possible. Retain such
+checks when their distinct protection justifies their cost. A one-time migration
+check must not silently become a permanent release requirement.
 
-- dependency or module hygiene appropriate to the language and ecosystem;
-- the complete deterministic, offline default test suite;
-- race, concurrency, or equivalent safety checks where the implementation can
-  be meaningfully checked for those risks;
-- static analysis and linting used by the repository;
-- production builds for every supported target that can be built in the
-  release environment;
-- formatting and whitespace checks;
-- validation of maintained examples, configuration, schemas, generated
-  sources, and documentation commands where applicable;
-- review of changed local documentation links;
-- removal of obsolete roadmap documents under `docs/roadmap/` that describe
-  completed work included in the release;
-- review for unintended files, generated output, credentials, private data,
-  and unrelated changes; and
-- any additional security, compatibility, migration, packaging, or platform
-  checks required by the product.
+The selected Go commands use readonly module mode with `GOPROXY=off`; acquire
+the baseline toolchain and dependencies before validation. Formatting and
+whitespace remain ordinary development checks in `scripts/check.sh`.
+Review module tidiness when dependencies change, not as a release gate.
 
-Unavailable tooling or an inapplicable check must be addressed explicitly in
-the adopted policy or release procedure; it must not disappear silently from
-the candidate gates.
+Release tests must not require real credentials, mutable application services,
+paid APIs, provider probes, or inference calls. The procedure may describe dependency
+preparation separately from offline validation.
 
-Run the complete checker while preparing the candidate. Commit the release
-note and all associated code, tests, documentation, and configuration, then
-run the complete checker again against the exact commit intended for release.
-Do not publish a release from uncommitted or unvalidated content.
+Avoid duplicate validation across release phases. Successful checks for the
+same final candidate need not be repeated solely to satisfy another phase;
+any reuse must clearly apply to that exact candidate. Persistent validation
+caches are not required. If the candidate changes, validate the new candidate.
+Cheap publication-state checks may be repeated immediately before pushing
+because local or remote state may have changed during validation.
+
+Automate mechanical guards. Human review gates are strongly disfavored: add one
+only through an explicit project-specific policy decision explaining the
+concrete risk and why ordinary change review or automation is insufficient.
+Do not add routine confirmations for checks the command can perform itself.
+
+Compatibility review, release-note accuracy, completed-roadmap retirement, and
+review for unintended files or credentials remain ordinary preparation. The
+executing agent may perform them without routine human approval or separate
+manual evidence records. Publication itself requires authorization.
 
 ## Publication Guards
 
-Immediately before publication, the maintainer or release automation must
-fetch the current primary branch and tags from the authoritative remote and
-verify all of the following:
+Automate the checks needed to publish the intended source under a fresh version:
 
-- the version has the required format and is not already published;
-- the current branch is the primary release branch;
-- the worktree and index are clean;
-- the current commit is the recorded, validated candidate;
-- the authoritative remote branch points to that same commit;
-- the matching release note exists in that commit and has the required title
-  and sections;
-- all required approvals and automated gates succeeded for that commit; and
-- no local or remote tag already uses the selected version.
+- the version has the adopted format and is unused locally and on the
+  authoritative remote;
+- the worktree and index are clean on the primary release branch;
+- the source being published is the exact candidate that passed validation,
+  including its matching release note;
+- the remote primary branch can be advanced to that candidate without
+  discarding remote history, and is published before the tag; and
+- the tag identifies the validated candidate and only the intended refs are
+  published.
 
-Create the version tag against the guarded commit and verify its target before
-publishing it. Publish only the exact intended ref and deliverables. Broad
-operations such as `git push --tags` are discouraged because they can publish
-unreviewed refs unrelated to the release.
+ConfigKit also checks that `origin` has exactly the authoritative fetch and
+push destination, including configured push URLs. The command checks the
+candidate and unused version again after validation, and checks local state
+before creating the tag. Ignored local files do not block publication.
 
-The repository-specific procedure must make these guards executable or give
-copyable commands for performing them.
+Fetch the authoritative branch and tag state as needed for these checks.
+Do not force branch or tag updates to bypass a failed guard. Publish explicit
+refs rather than all local tags. Do not require CI success, publication-service
+availability checks, or a separate manual confirmation for each guard.
 
 ## Immutability And Correction
 
-Published version tags and published deliverables are immutable. Do not move,
-overwrite, recreate, or delete a published tag. Do not replace an artifact,
-image, package, checksum, signature, provenance statement, or release note
-under an already published version.
+Published version tags and published contents are immutable. Do not move,
+overwrite, recreate, or delete a published tag, or replace a published artifact,
+checksum, signature, provenance statement, or release note under that version.
+The checked-in note at the immutable tag is that release's historical record.
 
-If validation fails before publication, correct the candidate, rerun the
-complete gates, and repeat the publication guards. An unpublished local tag
-may be removed after confirming that it was never published or used by a
-release channel.
+If validation fails before publication, correct and commit the candidate and
+rerun the publication command. If a push fails or its outcome is ambiguous,
+inspect the authoritative remote before retrying. Remove an unpublished local
+tag only after confirming it was never published or used by a release channel.
+An unavailable remote leaves publication status unknown; do not overwrite a tag
+to resolve uncertainty.
 
-If publication or post-publication verification reveals a defect, leave the
-published release intact. Correct the defect on the primary branch, choose a
-new patch version or other semantically appropriate new version, write a new
-matching release note, and perform the complete release procedure again.
+Transient network, authentication, CI, or consumer-availability failures do not
+by themselves require a new version.
 
-A distribution channel's supported yank, deprecation, or advisory mechanism
-may warn consumers away from a defective release, but it must not replace that
-release's contents or reuse its version.
+A defect requiring changes to published source or contents requires a corrected
+commit, a new semantically appropriate version, a matching release note, and
+the release procedure again. Leave the original release intact. A channel's
+yank, deprecation, or advisory mechanism may warn consumers away from a defective
+release without replacing its contents or reusing its version.
 
 ## Repository Release Procedure
 
-Every adopting repository must maintain `docs/release.md` as the canonical
-maintainer runbook for implementing this policy. It must define, in execution
-order:
+Maintain `docs/release.md` as a short, executable maintainer runbook. It must
+identify prerequisites, the primary branch and authoritative remote, version
+and note preparation, one publication command with local checks and guards,
+source-only deliverables, the successful-tag-push completion point, and
+partial or unknown-state recovery.
 
-1. maintainer prerequisites and required access;
-2. version selection and compatibility review;
-3. release-note creation;
-4. candidate preparation and the complete validation command;
-5. candidate commit, push, and exact commit recording;
-6. publication guards;
-7. exact tag and deliverable publication commands;
-8. authoritative remote and consumer-facing verification; and
-9. failure handling and correction.
-
-The procedure should use copyable, fail-fast commands where practical. It must
-name the primary branch, authoritative remote, tag form, published
-deliverables, supported build targets, release automation responsibilities,
-and consumer verification path. It must link to this policy instead of
-restating or redefining its requirements.
+Use copyable commands where practical. Keep optional diagnostics and consumer
+verification clearly optional. The procedure must not turn preparation work,
+ordinary change review, or post-publication investigation into additional
+release gates.
 
 ## Policy Exceptions
 
-### Temporary bootstrap deferral
+The following historical exceptions do not change the current release workflow.
 
-The release procedure (`docs/release.md`) and complete release-check command are
-not yet present because ConfigKit has no Go module or implementation to validate.
-Their creation is temporarily deferred during initial development. This exception
-permits implementation work; it does not permit publishing a release without
-any gate required above.
+For v0.1.1 only, the maintainer approved renaming the reserved `_configkit` key to
+`configkit` as an error-correcting point release because there are no current
+consumers. This intentionally changes the v0.1.0 configuration contract without a
+minor-version increment. The release note must explain the renamed directive,
+the lack of a legacy alias, and the newly reserved application key. This exception
+does not apply to subsequent releases or waive any validation or publication gate.
 
-Compensating controls: no release may be published until the
-[release-readiness gaps](../roadmap/release-readiness.md) are closed, the runbook
-and checker exist, and the exact candidate passes all applicable gates. The
-maintainer preparing the first release owns closure. Remove this temporary
-exception when readiness is verified. Any other exception requires a documented repository constraint, rationale,
-compensating controls, scope, and closure condition here; none is currently
-adopted. Do not silently weaken the base integrity, validation, documentation,
-verification, or immutability guarantees.
+For v0.2.0 only, the maintainer accepted the successful native macOS check at
+`244104f` for the final candidate, provided subsequent changes are documentation
+only. The final candidate still requires the complete Linux release checker.
+This exception waives only repeating the macOS check after those documentation
+changes; it does not waive other publication or verification gates.

docs/policy/testing.md

@@ -1,14 +1,16 @@
 # Testing Policy
 
-**Base Policy Version:** 1.0
+**Base Policy Version:** 1.3
 
-**Last Updated:** 2026-09-06
+**Last Updated**: 2026-09-28
+
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/testing.md)
 
 ## Purpose
 
 Our tests exist to make **incorrect changes expensive and correct changes cheap**.
 
-We do not optimize for test count, line coverage, exhaustive isolation, or the fewest possible tests. We optimize for sufficient confidence in important behavior while imposing as little unnecessary friction as possible on future development.
+We optimize for sufficient confidence in important behavior while minimizing friction on future development.
 
 ## ConfigKit-specific priorities
 
@@ -39,37 +41,24 @@ boundaries. No credential bytes may appear in inspection or failure fixtures'
 expected output; use disposable canaries to prove non-disclosure.
 
 Baseline commands belong in the [development guide](../development.md). Release
-gates belong in the [release policy](release.md) and its eventual runbook. This
+gates belong in the [release policy](release.md) and [maintainer runbook](../release.md). This
 policy does not imply that those tools or tests already exist.
 
 ## Every test has a cost
 
-Testing is not an unqualified good. Every test imposes both an immediate cost and a continuing lifetime cost.
-
-A test must be:
-
-- written and reviewed;
-- understood by future maintainers and coding agents;
-- executed in local and CI workflows;
-- diagnosed when it fails;
-- updated when legitimate behavior changes;
-- maintained as fixtures, APIs, and dependencies evolve; and
-- removed or rewritten when it becomes redundant, brittle, misleading, or obsolete.
-
-Tests also create cognitive and architectural friction. They can constrain refactoring, duplicate policy, slow feedback loops, add noise to failures, and cause harmless implementation changes to require unrelated edits across the suite.
+Every test has an immediate and continuing cost: writing, review, execution,
+diagnosis, fixture maintenance, and updates when legitimate behavior changes.
+Tests can also constrain refactoring, duplicate policy, and add failure noise.
 
 A test is warranted only when the confidence it provides justifies these costs.
-
-Apply this cost-benefit analysis at two levels:
+Evaluate that tradeoff at two levels:
 
 1. **Per test:** What realistic defect does this test detect, how consequential would that defect be, and is that protection worth the test's lifetime cost?
 2. **Across the suite:** Does this collection provide materially more confidence than a smaller, simpler suite would?
 
-The preferred test suite is a **lean suite that provides sufficient confidence in the risks that matter, without redundant or low-value tests**. We seek sufficient confidence with the least unnecessary testing friction, not the fewest possible tests.
+Some friction is intentional. Tests should make dangerous changes—such as breaking compatibility, corrupting data, violating security boundaries, or reintroducing subtle bugs—require deliberate review. Keep ordinary internal changes inexpensive.
 
-Some friction is intentional. Tests should make dangerous changes—such as breaking compatibility, corrupting data, violating security boundaries, or reintroducing subtle bugs—require deliberate review. They should not make ordinary internal changes needlessly expensive.
-
-The cost of a test is not a reason to omit testing by default. Do not cite maintenance cost abstractly. When omitting a plausible test, be able to state why the protected failure is low-risk, already covered, obvious, reversible, or cheaper to detect elsewhere. For consequential, subtle, or difficult-to-observe behavior, the presumption should favor testing.
+Evaluate maintenance cost against the specific failure being protected. When omitting a plausible test, be able to state why the protected failure is low-risk, already covered, obvious, reversible, or cheaper to detect elsewhere. For consequential, subtle, or difficult-to-observe behavior, the presumption should favor testing.
 
 ## Default testing style
 
@@ -81,6 +70,8 @@ Use a **classical/Detroit-style** approach:
 - Prefer package-level behavioral tests over tests coupled to private helpers or internal call sequences.
 - Treat exact collaborator interactions as testable behavior only when the interaction itself is a requirement.
 
+Examples of appropriate seams include clocks, randomness, subprocesses, remote APIs, object storage, email, and paid LLM calls.
+
 For ConfigKit, controlled input readers and filesystem failures are useful seams.
 Prefer actual parsing, composition, and decoding over mocks of their call order.
 
@@ -92,7 +83,7 @@ Control clocks, randomness, environment variables, and other process-global or m
 
 ## What deserves tests
 
-Prioritize tests for:
+To the extent the following features are present in the application, prioritize tests for:
 
 1. Public and package-level contracts.
 2. Domain rules and important invariants.
@@ -102,15 +93,27 @@ Prioritize tests for:
 6. Previously observed or plausible regressions.
 7. Representative integration and end-to-end workflows.
 
-A package-level contract is behavior relied upon by another package or major collaborator, not every observable detail of a package implementation.
+A package-level contract comprises behavior relied upon by another package or major collaborator.
 
-For behavior involving **data integrity, destructive operations, compatibility, security, concurrency, idempotency, or recovery**, presume that durable tests are required unless the behavior is already credibly protected at another layer.
+Choose tests for requested behavior and established contracts. Tests must not
+introduce new restrictions, guarantees, or threat scenarios merely because they
+could be asserted. Follow the [agent policy](agents.md) when deciding whether a
+behavior belongs to the contract; current implementation behavior alone is not
+sufficient authority.
+
+For established behavior involving **data integrity, destructive operations,
+compatibility, security, concurrency, idempotency, or recovery**, favor durable
+tests for realistic failures whose consequences warrant protection. Identify
+the failure and the existing contract it would violate. These categories call
+for attention, not an automatic test inventory or permission to strengthen the
+application's guarantees. Account for protection already provided at other layers.
 
 Do not add tests merely because a function, branch, or line exists. Do not add a test when the same meaningful risk is already adequately protected elsewhere.
 
 ## Choose the right test boundary
 
-Test through the narrowest stable boundary that expresses the behavior clearly.
+Choose the narrowest stable boundary that expresses the behavior clearly and
+provides durable confidence with minimal incidental coupling.
 
 This is often the package API, but it may instead be:
 
@@ -118,28 +121,15 @@ This is often the package API, but it may instead be:
 - a package-level operation when several internal collaborators jointly produce the behavior; or
 - a larger integration boundary when correctness emerges from interaction with a real dependency.
 
-Do not force all behavior through oversized end-to-end tests. Do not test every private helper merely because it exists. Choose the boundary that gives durable confidence with the least incidental coupling.
-
 ## Test behavior, not implementation
 
-A test should protect a decision, contract, or invariant—not memorialize the current implementation.
+A test should protect a selected decision, contract, or invariant.
 
-Before adding or retaining a test, ask:
+A test is suspect when it primarily detects changes to private constants or
+helpers, equivalent operation ordering, incidental formatting, equivalent
+algorithms, or internal structure that preserves behavior.
 
-> What realistic defect would this test catch?
-
-A test is suspect when its main purpose is to detect that someone:
-
-- changed an internal constant;
-- renamed or split a private helper;
-- reordered equivalent internal operations;
-- changed incidental formatting;
-- replaced one correct algorithm with another; or
-- refactored internal object structure without changing behavior.
-
-Refactoring should normally require no test edits unless the refactored structure is itself part of the contract.
-
-A test can be factually correct and still have negative value. Accurately describing current behavior is not enough; the protected behavior must be important enough to justify the future friction.
+Behavioral tests should normally remain stable through internal refactoring that preserves the contract.
 
 ## Expected effects of different changes
 
@@ -156,12 +146,13 @@ A test failing is not the same as a test needing to be edited. Many tests may co
 
 ## Separate mechanism from policy
 
-Configurable thresholds and defaults must not be duplicated throughout the test suite.
+Derive expectations from test-controlled configuration and relationships.
 
-For example, do not encode an internal concurrency limit indirectly:
+For this example, assume the selected contract rejects a request to start more
+processes than a configured limit. Do not encode its production default indirectly:
 
 ```go
-// Production policy:
+// Production default:
 const maxConcurrency = 4
 
 // Brittle test:
@@ -179,25 +170,30 @@ require.NoError(t, runner.Start(limit))
 require.ErrorIs(t, runner.Start(limit+1), ErrTooMuchConcurrency)
 ```
 
-The test should prove:
+For this selected contract, the test should prove:
 
 - the configured limit is accepted; and
 - one beyond the configured limit is rejected.
 
+Rejection is not a general requirement for concurrency control. If the selected
+contract queues excess work or limits active workers while accepting larger
+batches, test that behavior instead. Do not add rejection or a configurable
+limit solely to reproduce this example.
+
 The production default should be tested exactly only when its literal value is itself a public, operational, safety, protocol, or compatibility requirement.
 
-Apply the same rule to limits, timeouts, capacities, retry counts, and ranges: test relationships and behavior, not duplicated literals.
+Apply the same rule to limits, timeouts, capacities, retry counts, and ranges: test relationships and behavior.
 
-For concurrency limits, test both kinds of behavior when relevant:
+For established concurrency limits, distinguish these behaviors where the contract requires them:
 
-1. **Configuration enforcement:** invalid or excessive requested values are handled correctly.
+1. **Configuration handling:** values are accepted or rejected according to the selected contract.
 2. **Runtime enforcement:** observed peak concurrency never exceeds the configured limit.
 
-Use a test-controlled limit and measure the behavior relative to that limit. Do not merely assert today's default value.
+Use a test-controlled limit and measure the behavior relative to that limit.
 
-## Avoid semantic duplication across layers
+## Assign each behavior a test owner
 
-Each behavior should have a clear test owner.
+For ConfigKit, assign ownership as follows:
 
 - YAML boundary tests own syntax and policy enforcement.
 - Composition and overlay tests own their operation semantics.
@@ -209,9 +205,7 @@ Each behavior should have a clear test owner.
 
 These are responsibility boundaries, not a required package layout.
 
-Higher-level tests should not repeat every lower-level case. A single intentional policy change should not require unrelated edits across many test files.
-
-Tests that are individually reasonable may still be collectively redundant. Evaluate the marginal value of each additional test in light of the protection already provided by the rest of the suite.
+Give each layer its distinct responsibility and keep expectation updates localized to the contract being changed.
 
 ## Use test doubles deliberately
 
@@ -232,104 +226,77 @@ Mocks are appropriate when the contract includes facts such as:
 - an expensive API is called no more than once; or
 - a security audit event is emitted.
 
-Do not use mocks merely to isolate every object or reproduce the implementation's call graph.
-
 ## Go-specific guidance
 
-Use:
+Select techniques by behavior and risk:
 
 - table-driven tests for meaningful behavioral categories and boundaries;
 - `t.TempDir()` for real filesystem behavior;
-- fuzz tests for parsers, normalization, path handling, and broad input spaces;
+- `httptest.Server` for realistic HTTP interactions;
+- fuzz tests when exploring broad input spaces, such as parsers or path handling, adds useful protection beyond representative cases;
 - golden files only when the complete output is intentionally stable;
 - integration tests where correctness depends on component interaction; and
-- a small number of representative end-to-end tests.
+- a small number of representative end-to-end tests when assembled workflows expose meaningful risks not adequately covered at narrower boundaries.
 
-Avoid exact error-string assertions unless the wording is itself contractual. Prefer `errors.Is`, `errors.As`, typed errors, or structured error fields.
+Prefer `errors.Is`, `errors.As`, typed errors, or structured error fields. Use exact error-wording assertions only when the wording is contractual.
 
 At the public library boundary, prefer diagnostic codes, paths, and source
 locations over complete message snapshots. Assert wording only when contractual.
 
 Golden-file updates must require an explicit local flag. CI must not update golden files automatically, and reviewers must inspect the semantic diff before accepting an update.
 
-Keep tests readable and direct. Test helpers and fixture frameworks must earn their own maintenance cost; do not build elaborate test infrastructure for small or isolated needs.
+Keep tests readable and direct. Size test helpers and fixture frameworks to the maintenance benefit they provide.
 
 ## Coverage
 
-Coverage is a diagnostic, not a target.
+Use coverage to locate untested critical branches and unexpectedly weak packages. Evaluate test quality through meaningful behavioral protection and choose coverage according to risk.
 
-Use it to find untested critical branches and unexpectedly weak packages. Do not write low-value tests solely to increase a percentage, and do not infer test quality from coverage alone.
-
-Dense configuration semantics will often warrant higher coverage than simple input wiring. Uneven coverage is acceptable when it reflects risk.
-
-Increasing coverage is valuable only when the newly covered behavior protects a meaningful risk at an acceptable cost.
+Pure domain logic will often warrant higher coverage than CLI wiring or external adapters. Uneven coverage is acceptable when it reflects risk.
 
 ## Regression tests
 
 A bug fix should normally include a regression test that fails before the fix and passes afterward.
 
-Retain the test when the defect could realistically recur and its consequences justify the ongoing cost. Prefer the narrowest durable test of the violated contract or invariant; do not preserve accidental implementation details from the original bug.
+Retain the test when the defect could realistically recur and its consequences justify the ongoing cost. Prefer the narrowest durable test of the violated contract or invariant.
 
-Not every historical bug requires a permanent test. If the underlying design has made recurrence impossible, the test has become redundant, or a stronger invariant test now subsumes it, remove or consolidate it.
+Remove or consolidate a test when the underlying design has made recurrence impossible, its protection is redundant, or a stronger invariant test subsumes it.
 
 ## Deleting or rewriting tests
 
-Tests are maintained code, not permanent historical artifacts.
-
-Delete or rewrite a test when its maintenance cost exceeds the confidence it provides.
+Delete or rewrite tests when maintenance cost exceeds their continuing
+protective value.
 
 Strong candidates include tests that:
 
 - require updates after harmless internal changes;
-- directly assert private constants without protecting a real contract;
-- duplicate the same policy across several layers;
+- assert incidental private constants or snapshot large amounts of incidental output;
 - verify mock choreography rather than outcomes;
-- snapshot large amounts of incidental output;
-- test trivial private helpers already exercised through stable package behavior;
-- protect risks already covered more effectively elsewhere;
+- duplicate policy across layers, retest trivial helpers covered by package
+  behavior, or protect risks covered more effectively elsewhere;
 - are flaky, misleading, obsolete, or disproportionately expensive to diagnose; or
 - no longer correspond to a plausible failure mode.
 
-Several brittle tests may encode one genuine requirement. Replace them with one durable behavior-level or invariant test rather than preserving all of them.
-
-Deleting a low-value test can improve the quality of the suite by reducing noise, maintenance burden, and friction around legitimate change.
+Several brittle tests may encode one genuine requirement. Consolidate them into one durable behavior-level or invariant test.
 
 ## Reviewing a proposed test
 
-Use the following questions when the value, boundary, or durability of a proposed test is not self-evident. Significant test additions should be reviewable against them, but written answers are not required for every routine test.
+Use the following questions when a proposed test needs closer evaluation. Significant test additions should be reviewable against them; written answers are optional for routine tests.
 
-1. What realistic defect would it catch?
-2. How likely is that defect?
-3. How consequential would it be?
-4. Is the behavior already protected elsewhere?
-5. At which layer should this behavior be owned?
-6. Does the test assert a durable contract or an incidental implementation detail?
-7. Could the implementation be refactored without changing the behavior and without editing this test?
-8. What should cause this test to fail?
-9. What legitimate changes should not cause this test to fail?
-10. What ongoing maintenance, execution, and diagnostic cost will the test impose?
-11. Is there a smaller or more direct test that protects the same risk?
-
-Do not add the test when its expected lifetime cost exceeds its expected protective value.
-
-When deciding not to test plausible behavior, record or be able to explain why the risk is low, already protected, obvious, reversible, or cheaper to detect elsewhere.
+1. Which requested behavior or established contract does it protect, and what realistic defect would violate it?
+2. How likely and consequential is that defect, and is it already protected elsewhere?
+3. What is the narrowest stable boundary that can test it clearly?
+4. Would a correct internal refactor or a change to an incidental default require test edits?
+5. Does its confidence justify its maintenance, execution, and diagnostic cost, or would a smaller test suffice?
 
 ## Definition of sufficient
 
 A test suite is sufficient when:
 
-- important contracts and invariants are protected;
-- meaningful boundaries and failure modes are exercised;
-- realistic and consequential regressions are credibly protected against silent recurrence;
-- behavior involving data integrity, destructive operations, compatibility, security, concurrency, idempotency, and recovery is credibly protected;
-- important external boundaries have realistic integration coverage;
-- representative complete workflows are tested;
-- failures provide useful signal rather than redundant noise;
-- legitimate internal changes usually do not require test edits; and
+- important requested behavior and established contracts are protected against realistic, consequential failures;
+- boundaries and component interactions have coverage where they introduce meaningful risks not protected elsewhere;
+- failures provide useful, distinct signals;
+- tests usually remain stable through legitimate internal changes; and
 - additional tests would mostly repeat existing protection or preserve inconsequential implementation details.
 
-Sufficiency is a risk judgment, not a coverage percentage or test count. Reassess it as the library, its consumers, and the consequences of failure evolve.
-
-The governing rule is:
-
-> Test heavily where failure is consequential, subtle, or difficult to detect after the fact. Test lightly where failure is obvious, reversible, and inexpensive—and retain no test whose lifetime cost exceeds the confidence it provides.
+Reassess sufficiency as the application, its users, and the consequences of
+failure evolve.

docs/release.md

@@ -0,0 +1,199 @@
+# ConfigKit Release Procedure
+
+This is the maintainer runbook for ConfigKit's [release policy](policy/release.md).
+ConfigKit publishes one source-only Go module. The immutable annotated tag and
+matching checked-in release note are the deliverables; there is no binary,
+container image, generated package, or separate registry publication.
+
+## Release identity and support
+
+- Module: `gitea.maximumdirect.net/eric/ConfigKit`
+- Primary branch: `main`
+- Authoritative remote: `origin`, with fetch and push destination
+  `https://gitea.maximumdirect.net/eric/ConfigKit.git`
+- Tags: stable Semantic Versions such as `v0.5.0`; no prereleases
+- Minimum Go line: Go 1.25, validated with one maintained patch
+- Release-gated targets: Linux amd64 and arm64
+- Best-effort targets: macOS amd64 and arm64, under the
+  [platform support policy](policy/release.md#platform-support)
+
+The checker runs one offline race suite, one full vet pass, and CGO-disabled
+builds for both Linux targets. It reports skipped filesystem cases. macOS checks
+and newer-toolchain tests are optional. CI is never a readiness or completion
+gate; do not wait for or poll it.
+
+## 1. Prepare access and tools
+
+Use a clean checkout with Git, Bash 3.2 or newer, a maintained Go 1.25 patch,
+and a native compiler for race tests. Configure private-host access through the
+normal credential manager. Keep credentials and environment dumps outside the
+repository and command transcript.
+
+Verify access without displaying credentials:
+
+```sh
+git remote get-url origin
+git ls-remote origin HEAD
+```
+
+The fetch URL and all configured push destinations must resolve to the
+authoritative URL above. The publication command checks this again. Acquire the
+selected toolchain and dependencies explicitly before offline validation:
+
+```sh
+export CONFIGKIT_BASELINE_TOOLCHAIN=go1.25.14
+GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go version
+GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go mod download
+```
+
+A maintained patch may replace the example pin. No per-release latest-version
+survey is required. Dependencies must be cached; the checker sets `GOPROXY=off`.
+Publication requires user authorization. Standing authorization for local
+commits does not authorize a push or release.
+
+## 2. Select the version and review compatibility
+
+Choose an unused stable version. Compare the candidate with the previous tag.
+Review exported Go signatures and ownership, YAML and scalar semantics,
+precedence, diagnostic codes, minimum Go version, and platform support. A
+signature-preserving change may still affect consumers. Before `v1.0.0`,
+intentional incompatible minor-release changes need a note explaining impact
+and consumer action; patch releases remain compatible within their minor line.
+Review the maintained consumer examples and migration guide.
+
+When dependencies change, review parser behavior and migration impact as part
+of that change. Module tidiness belongs to dependency-change review, not the
+release checker. Do not repeat a dependency-version survey for every release.
+
+## 3. Write and commit the release note
+
+Create `docs/releases/<version>.md` for the selected version. Its first line
+must be `# ConfigKit <version>`. Give a meaningful summary and include
+compatibility impact or upgrade instructions when applicable. Link to current
+contracts for exact behavior. Review the note and affected canonical documents
+as ordinary preparation, then commit the complete candidate.
+
+End every new note with these links, replacing `VERSION` with the complete tag:
+
+```markdown
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/docs/oss/attribution.md)
+```
+
+Confirm the three target files exist in the candidate and review the version in
+the URLs. The future tag need not resolve remotely yet; this review adds no
+network gate. ConfigKit uses checked-in notes without hosted release objects.
+If a hosted page is used later, reuse the note and preserve its footer. Do not
+rewrite historical notes or add downloadable license assets.
+
+## 4. Publish the committed candidate
+
+Before publication, review compatibility, release-note accuracy, and the file
+list for unintended content or credentials. Retire completed roadmaps as part of
+release preparation, preserving unfinished and deferred work and repairing
+links. These are ordinary preparation tasks, not separate human sign-offs.
+
+With the release explicitly authorized, run the one publication command.
+The script resolves the repository root from its own path, so it may be invoked
+from another directory by using its path there. Replace the sample version with
+the selected version:
+
+```sh
+./scripts/release.sh v0.5.0
+```
+
+The command requires `main`, a clean index/worktree, an unused version locally
+and on the authoritative remote, and a matching note in the captured commit.
+Ignored local files do not block it. It checks remote ancestry, runs
+[`release-check.sh`](../scripts/release-check.sh) once against that commit,
+rechecks candidate and version state, pushes only that commit to `main`, then
+creates and pushes one annotated tag. The tag message is the checked-in note.
+It never commits or repairs the checkout.
+
+A successful intended tag push completes publication. The command reports the
+version and commit immediately. No CI, module retrieval, remote read-back, or
+hosted release object is required. The checker may be run separately for
+diagnosis, but it is not a prerequisite: a fresh publication invocation
+validates its candidate once.
+
+## 5. Recover from a failed or uncertain push
+
+The command performs one bounded authoritative-state check after a failed push.
+If the main push failed but authoritative main equals the candidate, it proceeds.
+If the tag push failed but its exact tag object reached the remote, it reports
+success. Otherwise it reports branch-only, conflicting, or unknown state and
+retains any local tag.
+
+Inspect exact refs before any retry. Set `release_version` to the attempted
+version and compare main with the candidate from the command's report:
+
+```sh
+release_version=v0.5.0
+authoritative=https://gitea.maximumdirect.net/eric/ConfigKit.git
+if remote_main=$(git ls-remote --refs --exit-code "$authoritative" refs/heads/main); then
+  printf 'remote main: %s\n' "$remote_main"
+else
+  result=$?
+  if [ "$result" -eq 2 ]; then
+    printf 'authoritative main confirmed absent\n' >&2
+  else
+    printf 'remote main state unknown; inspect before retrying\n' >&2
+  fi
+fi
+ref="refs/tags/$release_version"
+if remote_tag=$(git ls-remote --refs --exit-code "$authoritative" "$ref"); then
+  printf 'remote tag: %s\n' "$remote_tag"
+else
+  result=$?
+  if [ "$result" -eq 2 ]; then
+    printf 'remote tag confirmed absent\n'
+  else
+    printf 'remote tag state unknown; do not reuse the version\n' >&2
+  fi
+fi
+if local_tag=$(git rev-parse --verify "refs/tags/$release_version" 2>/dev/null); then
+  printf 'local tag object: %s\n' "$local_tag"
+else
+  printf 'no local tag object\n'
+fi
+```
+
+A query failure is not proof that the tag is absent. Compare the remote tag
+object ID with the local annotated tag object ID; its peeled commit alone is
+insufficient to establish identical publication. A conflicting published tag
+must not be moved or replaced. If remote main advanced but the tag was not
+published, report that partial progress. Only after confirming the local tag
+was never published or used by another channel may a maintainer remove it:
+
+```sh
+git tag -d "$release_version"
+```
+
+A subsequent invocation revalidates the candidate; a correctly published tag
+needs no rerun. Do not roll back main or automatically delete a tag. Transport
+or authentication failure alone does not require a new version. A defect in
+published source requires a corrected commit, a new semantically appropriate
+version and note, and the release procedure again.
+
+## 6. Optional consumer verification
+
+Only when useful or requested, read back the remote tag or retrieve the exact
+version into a new module without a local `replace` directive. These checks
+are optional and non-gating. Do not poll CI or wait for module propagation.
+Private-host credentials must already be configured. For direct-origin
+verification, set the version to the release just published (replace the sample
+below), then use a temporary consumer module and check the exact module path
+and version reported by `go list -m`:
+
+```sh
+release_version=v0.5.0
+consumer_dir=$(mktemp -d)
+(
+  cd "$consumer_dir"
+  go mod init example.invalid/configkit-release-check
+  GOPRIVATE=gitea.maximumdirect.net GOPROXY=direct go get "gitea.maximumdirect.net/eric/ConfigKit@$release_version"
+  go list -m -f '{{.Path}} {{.Version}}' gitea.maximumdirect.net/eric/ConfigKit
+)
+```
+
+The output should show the exact module path and selected version. Report this
+optional check separately from publication success.

docs/releases/v0.1.0.md

@@ -0,0 +1,72 @@
+# ConfigKit v0.1.0
+
+This is the first source release of ConfigKit, an opinionated Go library for strict,
+explainable YAML configuration loading.
+
+## Summary
+
+ConfigKit provides one typed loading lifecycle for file, byte, reader, and
+defaults-only inputs. It supports bounded explicit imports, strict composition,
+selected profiles, explicit CLI overrides, application-owned defaults and recorded
+resolution, semantic validation, provenance, redacted effective output, and safe
+historical explanation.
+
+Typed environment-name secret references and an explicit secrets-directory bootstrap
+keep credential acquisition separate from ordinary loading. Maintained consumer
+examples demonstrate simple and composed application shapes without exposing the
+private YAML parser dependency.
+
+See the [configuration contract](../config.md) and
+[consumer adoption guide](../consumers/README.md) for current behavior and examples.
+
+## Compatibility
+
+This is the initial public release, so there is no earlier ConfigKit release to
+upgrade from. The module requires Go 1.25 or newer and supports Linux and macOS on
+amd64 and arm64. Candidate validation uses patched Go 1.25 and Go 1.26 toolchains;
+native Linux and macOS evidence is required in addition to cross-builds.
+
+Configuration intentionally uses a strict YAML subset. Duplicate keys, aliases,
+anchors, merge keys, unsupported tags and scalar forms, trailing documents, and
+unknown typed fields are rejected. Composition rejects overlapping non-mapping
+definitions; replacement occurs only through selected profiles, explicit CLI
+overrides, or recorded application resolution.
+
+The private parser dependency remains explicitly pinned to
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`, which was still the newest available v4 release when
+the candidate was prepared. No upstream YAML declarations are part of ConfigKit's
+public API.
+
+## Upgrade
+
+No action is required for an earlier ConfigKit version because this is the first
+release. New consumers can add the module with:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.1.0
+```
+
+The authoritative host may require its normal private-module credentials. Consumers
+adapting existing application configuration should review the intentional migration
+differences in the [consumer adoption guide](../consumers/README.md), particularly
+strict YAML, string schema versions, explicit empty/null behavior, canonical module
+objects, `int64` dynamic integers, explicit CLI records, and typed secret references.
+
+## Changes
+
+- Added opaque file, byte, reader, and defaults-only sources with fixed resource
+  limits and safe structured diagnostics.
+- Added an owned strict YAML model, typed schema binding, detached defaults and
+  results, canonical projection, and private parser isolation.
+- Added explicit path/glob imports, deterministic strict composition, canonical
+  source identity and containment, and selected profile overlays.
+- Added layered presence, origins, chronological history, version checks, recorded
+  defaulting and normalization, and read-only semantic validation.
+- Added secret classification, deterministic redacted effective YAML, typed
+  environment references, and bounded explicit secrets-directory bootstrap reports.
+- Added parser-neutral explicit CLI overrides and safe structured/human historical
+  value explanations, including removed and superseded values.
+- Added maintained Narratio-, Notarius-, WeatherReporter-, and Seriatim-shaped
+  examples and migration coverage using only ConfigKit and the standard library.
+- Added race and bounded fuzz coverage plus a two-toolchain, offline, cross-platform
+  source-release checker and maintainer runbook.

docs/releases/v0.1.1.md

@@ -0,0 +1,43 @@
+# ConfigKit v0.1.1
+
+This release corrects the spelling of ConfigKit's reserved configuration key.
+
+## Summary
+
+The reserved directive key is now `configkit` instead of `_configkit`. Import
+declarations continue to use the same `imports` sequence and path/glob syntax.
+See the [configuration contract](../config.md#explicit-imports).
+
+## Compatibility
+
+This is an intentional configuration compatibility change, approved as a one-time
+[patch-release exception](../policy/release.md#policy-exceptions) because there are
+no current consumers. `_configkit` is no longer a directive or a reserved key; it
+is ordinary application data and is subject to normal schema validation. There is
+no legacy alias. `configkit` is now reserved, including in nested mappings, profiles,
+and override paths and values.
+
+The Go API, diagnostic codes, Go minimum version, and supported platforms are
+unchanged. The private YAML dependency remains pinned to
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`, confirmed as the newest available v4 release
+during candidate preparation.
+
+## Upgrade
+
+Rename `_configkit` directive keys to `configkit` in root configuration files and
+imported fragments. Rename any application-owned `configkit` fields to avoid the
+newly reserved key. Update diagnostic-path expectations to the new spelling.
+Files retaining `_configkit` will not load their declared imports.
+
+Consumers can select this release with:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.1.1
+```
+
+## Changes
+
+- Renamed the directive key consistently across imports, profiles, and overrides.
+- Updated current configuration documentation and the composed consumer fixture.
+- Updated behavioral tests and added coverage proving the old spelling is not an
+  import alias.

docs/releases/v0.1.2.md

@@ -0,0 +1,50 @@
+# ConfigKit v0.1.2
+
+This release adds safe enumeration of effective and removed metadata paths.
+
+## Summary
+
+`Metadata.HistoricalPaths` returns the semantic paths observed during a load,
+including paths removed by profiles, CLI overrides, or recorded resolution. This
+allows applications to discover hidden declarations and inspect their ownership
+through the existing `Metadata.History` API without reloading configuration or
+resolving unselected credentials.
+
+See the [layered metadata contract](../config.md#layered-metadata) for current
+behavior.
+
+## Compatibility
+
+This is a backward-compatible API addition. Existing APIs, configuration syntax,
+diagnostic codes, minimum Go version, and supported platforms are unchanged.
+Existing consumers do not need to change their code or configuration.
+
+Returned paths are detached, unique by canonical JSON Pointer spelling, and sorted
+by that spelling. The enumeration includes defaults and the root, exposes no
+configuration values, and performs no I/O or secret resolution.
+
+The private YAML dependency remains pinned to
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`, confirmed as the newest available v4 release during
+candidate preparation.
+
+## Upgrade
+
+No action required. Consumers that want historical path discovery can update with:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.1.2
+```
+
+Then iterate over `result.Metadata().HistoricalPaths()` and use `History` for
+chronological definitions or `Lookup` to determine whether each path remains
+effective.
+
+## Changes
+
+- Added `Metadata.HistoricalPaths` with detached, deterministic path enumeration.
+- Included effective, default, and removed paths while excluding paths that never
+  existed.
+- Added coverage for parent removal, mapping-to-sequence shape replacement, escaped
+  mapping keys, detached results, zero metadata, composite base ownership, and
+  avoidance of superseded secret lookup.
+- Documented historical path enumeration in the current configuration contract.

docs/releases/v0.2.0.md

@@ -0,0 +1,58 @@
+# ConfigKit v0.2.0
+
+This release adds integer schema-version input and consistent canonical sequence
+path handling.
+
+## Summary
+
+Applications can retain YAML such as `version: 4` while storing and checking their
+version as a Go string. The exception applies only to the path designated by
+`VersionRule`; unrelated fields keep strict decoding. See the
+[configuration contract](../config.md#application-schema-versions).
+
+## Compatibility
+
+This minor release intentionally changes integer schema-version input from a
+`version.type` rejection to invoking the application checker with its decimal text.
+Plain string destinations at that path now accept it. Public Go API shapes,
+minimum Go version, and supported platforms are unchanged.
+
+Parsed sequence indices now require canonical nonnegative decimal spelling.
+Signed tokens such as `+0` and `-0`, previously accepted by some traversal paths,
+no longer identify sequence elements. They remain valid literal mapping keys.
+Version checking, decoding, and metadata matching now agree on this boundary.
+
+The private YAML dependency remains pinned to `go.yaml.in/yaml/v4 v4.0.0-rc.6`,
+confirmed as the newest available v4 release during candidate preparation. Linux
+candidate checks use Go 1.25.5 and Go 1.26.7. The maintainer confirmed native macOS
+checks at `244104f` and approved carrying that result across the documentation-only
+candidate changes under the [recorded exception](../policy/release.md#policy-exceptions).
+
+## Upgrade
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.2.0
+```
+
+Existing string schema versions need no configuration changes. Applications using
+integer YAML versions can retain them and use a plain string field plus a
+`VersionRule`. Review the application checker: it now receives integer identifiers
+as text, and remains responsible for rejecting unsupported versions. Fractions,
+exponents, booleans, and containers remain invalid version kinds.
+
+Replace signed sequence-index tokens in configured paths with canonical indices
+(for example, `/versions/+0` becomes `/versions/0`). Do not change signed mapping
+keys. Literal integers elsewhere still do not decode into strings, and numeric
+destinations retain their existing range checks.
+
+## Changes
+
+- Added load-local, path-scoped integer-to-string schema-version decoding without
+  mutating original input or introducing general scalar coercion.
+- Preserved numeric historical input, string effective output, decoding
+  reconciliation, source attribution, and secret redaction.
+- Unified sequence path interpretation and added regression coverage for signed
+  tokens, literal mapping keys, and explicit key/index distinctions.
+- Updated maintained Notarius-shaped fixtures and migration guidance for quoted
+  and integer version forms.
+- Retired completed implementation and remediation roadmaps to Git history.

docs/releases/v0.3.0.md

@@ -0,0 +1,70 @@
+# ConfigKit v0.3.0
+
+This release adds source provenance during application resolution, separates the
+public API from its internal engine, and moves macOS to best-effort support.
+
+## Summary
+
+Resolvers can query fixed entry-state metadata and already-acquired sources using
+`Resolution.InputInfo` and `Resolution.Source`. This supports application-owned
+decisions such as resolving relative paths against their declaring configuration
+files. See the [resolution contract](../config.md#recorded-application-resolution)
+and the maintained [source-aware path example](../consumers/README.md#source-aware-application-path-policy).
+
+The root `configkit` package now owns public types and explicit wrappers around a
+single private engine. Internal changes no longer automatically expand public
+method sets through shared type aliases. See the [component overview](../internal/overview.md)
+and [facade decision](../adr/0006-public-facade.md).
+
+## Compatibility
+
+Existing consumer imports, exported API signatures, configuration syntax,
+precedence, secret handling, callback lifetime, and ownership behavior are
+preserved. The two resolution query methods are additive and available only
+during an active resolution callback; returned records remain detached. The
+library supplies provenance, not a new filesystem normalization policy.
+
+macOS on amd64 and arm64 is now best-effort rather than release-validated.
+Neither native macOS evidence nor Darwin cross-builds are required for publication,
+and macOS-specific failures do not by themselves block a release. Linux on amd64
+and arm64 retains release-gated builds and native Linux validation. See the
+[platform support policy](../policy/release.md#platform-support).
+
+The module still requires Go 1.25 or newer. The private YAML dependency remains
+pinned to `go.yaml.in/yaml/v4 v4.0.0-rc.6`, confirmed as the newest available v4
+release during preparation. It is still a prerelease dependency, isolated behind
+the existing private parser boundary; no dependency upgrade is included.
+
+Linux candidate validation uses Go 1.25.14 and Go 1.26.8, including the complete
+release checker, race tests, consumer examples, filesystem fixtures, and Linux
+cross-builds. No native macOS validation is claimed for this candidate.
+
+## Upgrade
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.3.0
+```
+
+No code or configuration migration is required for the facade refactor. Adopt the
+new provenance queries only if your resolver needs them. Applications retain
+ownership of relative-path bases and fallback/error behavior.
+
+macOS consumers should account for the reduced validation commitment and perform
+their own application checks when upgrading if macOS behavior is important to
+their deployment.
+
+## Changes
+
+- Added callback-scoped, fixed entry metadata and source lookup without additional
+  filesystem access or credential resolution.
+- Added a maintained Notarius-shaped path-normalization example with provenance,
+  frozen effective output, and explanation coverage.
+- Moved loading, schema, resolution, provenance/history, secret, and rendering
+  machinery into one internal engine while keeping public named types root-owned.
+- Added exact-type secret and callback adapters, with regression coverage for
+  missing version checkers and nil/zero closed-context failures.
+- Added type-aware public-boundary checks covering aliases, collections, generic
+  constraints, and exported method sets; restored public reference documentation.
+- Removed macOS release gates and retained required Linux validation.
+- Retired completed feature, implementation, and remediation documents to Git
+  history and repaired navigation to current contract and component owners.

docs/releases/v0.3.1.md

@@ -0,0 +1,43 @@
+# ConfigKit v0.3.1
+
+This release fixes secrets-directory bootstrap when the directory contains Git
+metadata or other dot-prefixed entries.
+
+## Summary
+
+`LoadSecretsDir` now ignores dot-prefixed files, directories, and symlinks,
+including `.git`, `.gitignore`, and `.DS_Store`. These entries no longer prevent
+otherwise valid secrets from loading and are omitted from the bootstrap report.
+See the [bootstrap contract](../config.md#explicit-secrets-directory-bootstrap).
+
+## Compatibility
+
+This is a backward-compatible bug fix for previously rejected directory contents.
+There are no Go API signature changes or migrations for previously accepted
+inputs. Validation of non-hidden entries, existing-environment precedence, and
+the existing enumeration and content limits remain unchanged. Hidden entries
+still count toward the directory enumeration limit.
+
+The minimum Go version remains 1.25. Linux remains release-validated and macOS
+remains best-effort. The explicitly pinned YAML dependency remains
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`; reassessment found no newer published version.
+Retaining this prerelease pin avoids unrelated parser changes in this patch.
+
+## Upgrade
+
+Update the module dependency and rebuild the consuming application:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.3.1
+```
+
+No configuration migration is required. A secrets directory can retain its
+dot-prefixed metadata without treating those entries as secret candidates.
+
+## Changes
+
+- Filter hidden entries before filename and metadata validation and reporting.
+- Cover hidden-only and mixed directories, including Git metadata and a dangling
+  hidden symlink, with regression tests.
+- Update public API comments and the canonical bootstrap contract.
+- Stop tracking local codebase-memory tooling artifacts and ignore their directory.

docs/releases/v0.4.0.md

@@ -0,0 +1,56 @@
+# ConfigKit v0.4.0
+
+This release renames selected configuration profiles to overlays, intentionally
+breaking the previous naming contract without compatibility aliases or fallback.
+
+## Summary
+
+Selected configuration now uses `Options.Overlay` and `overlays/<name>.yml`.
+Selection, merge rules, input precedence, and lifecycle behavior are unchanged.
+See the [selected-overlay contract](../config.md#selected-overlays).
+
+## Compatibility
+
+This is a breaking minor release before v1.0.0. Four surfaces change:
+
+- Go API: `Options.Profile` becomes `Options.Overlay`, `LayerProfile` becomes
+  `LayerOverlay`, and all seven `CodeProfile*` constants become `CodeOverlay*`.
+- Selected files: `profiles/<name>.yml` becomes `overlays/<name>.yml`; there is
+  no legacy-directory fallback.
+- Provenance: the layer string changes from `profile` to `overlay`.
+- Structured diagnostics: the `profile.*` code prefix becomes `overlay.*`.
+
+The old Go identifiers are removed. Application-owned concepts such as
+`ModelProfile` and `model_profile` are unchanged. Ordinary explicit imports from
+a directory named `profiles` remain valid base inputs.
+
+The minimum Go version remains 1.25. Linux remains release-validated and macOS
+remains best-effort. The YAML dependency remains pinned to
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`; this release does not change parser dependencies.
+
+## Upgrade
+
+Update the dependency:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.4.0
+```
+
+Rename the affected Go identifiers, move selected files into `overlays/`, update
+any handling of provenance-layer and diagnostic-code strings, and rebuild.
+The maintained example helper is now `LoadNarratioOverlay` rather than
+`LoadNarratioProfile`. Application CLI flag names remain application-owned;
+ConfigKit does not require renaming domain-specific profile concepts.
+See the [migration guide](../consumers/README.md#selected-overlay-migration).
+
+## Changes
+
+- Rename the selected feature consistently across the public facade, internal
+  engine, diagnostics, source labels, examples, and current documentation.
+- Add regression coverage for the new directory, absence of legacy fallback,
+  public values, explanations, and preservation of application profile fields.
+- Align contributor policies with the current shared standard.
+- Simplify release validation to one local minimum-toolchain check. CI is not a
+  release gate; successful publication of the intended tag completes the
+  source-only release. See the [release procedure](../release.md).
+- Retire completed overlay and release-workflow planning documents to Git history.

docs/releases/v0.4.1.md

@@ -0,0 +1,42 @@
+# ConfigKit v0.4.1
+
+This release formalizes ConfigKit's licensing and upstream attribution
+documentation without changing library behavior.
+
+## Summary
+
+ConfigKit now includes an explicit LGPL-3.0-or-later grant in COPYRIGHT,
+complete LGPLv3 and incorporated GPLv3 license texts, and centralized upstream
+attribution. README and release guidance provide navigation to those materials.
+
+## Compatibility
+
+No Go code, public API, configuration semantics, diagnostic behavior, or
+dependencies changed from v0.4.0. The minimum Go version remains 1.25, Linux
+remains release-validated, and macOS remains best-effort. The YAML dependency
+remains `go.yaml.in/yaml/v4 v4.0.0-rc.6`.
+
+The project grant is explicitly LGPL-3.0-or-later. Third-party material remains
+subject to its respective terms, recorded in the attribution document below.
+Published earlier releases are unchanged.
+
+## Upgrade
+
+Update the module dependency and rebuild to select this release:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.4.1
+```
+
+No application-code or configuration migration is required from v0.4.0.
+
+## Changes
+
+- Add the project COPYRIGHT statement and complete standard project license texts.
+- Document go-yaml attribution with exact upstream revision links and local
+  Apache-2.0 and MIT license texts.
+- Adopt the house OSS policy and connect licensing ownership and contributor guidance.
+- Add license and attribution navigation to README and future release documents,
+  without adding release gates or changing publication mechanics.
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.1/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.1/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.1/docs/oss/attribution.md)

docs/releases/v0.4.2.md

@@ -0,0 +1,45 @@
+# ConfigKit v0.4.2
+
+This patch release simplifies and safeguards source publication and aligns
+maintainer policy and licensing guidance. Library behavior is unchanged.
+
+## Summary
+
+Maintainers can now publish a prepared release with one guarded command. It
+validates the exact committed candidate, checks the authoritative destination,
+and pushes only the candidate on `main` and its annotated version tag. The
+[release procedure](../release.md) explains preparation and partial-publication
+recovery; successful tag publication completes the source-only release without
+waiting for CI or consumer retrieval.
+
+## Compatibility
+
+No Go code, public API, configuration semantics, diagnostic behavior, or
+dependencies changed from v0.4.1. The minimum Go version remains 1.25. Linux
+amd64 and arm64 remain release-validated; macOS remains best-effort. The YAML
+dependency remains `go.yaml.in/yaml/v4 v4.0.0-rc.6`.
+
+## Upgrade
+
+Select this version and rebuild:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.4.2
+```
+
+No application-code or configuration migration is required from v0.4.1.
+
+## Changes
+
+- Add guarded single-command publication with exact candidate, version, and
+  remote checks; note-derived annotated tags; and bounded failed-push recovery.
+- Keep one offline race suite, one full vet pass, and Linux amd64/arm64 builds
+  as release gates. Formatting and whitespace remain development checks;
+  dependency tidiness is reviewed when dependencies change.
+- Align adopted policies and contributor guidance with their pinned upstream
+  revision, and include the CC BY-SA 4.0 license text and attribution for
+  adapted policy material. The project grant remains LGPL-3.0-or-later.
+- Retire completed release-workflow and policy-alignment planning records while
+  preserving their history in Git. Deferred scope remains documented.
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.2/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.2/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.4.2/docs/oss/attribution.md)

docs/roadmap/deferred.md

@@ -0,0 +1,28 @@
+# Deferred Scope
+
+This document owns intentionally excluded features, not a committed delivery plan.
+The [architecture policy](../policy/architecture.md) governs changes to these
+boundaries. Implemented behavior belongs in the [configuration contract](../config.md)
+and consumer adoption in the [consumer guide](../consumers/README.md).
+
+## Explicit non-goals and deferred scope
+
+General environment-variable configuration overlays are not supported. Typed secret
+references and explicit directory bootstrap are the environment convention. Literal
+credential configuration and implicit secret-directory discovery are unsupported.
+
+The initial release deliberately excludes:
+
+- automatic `conf.d` discovery;
+- remote imports, arbitrary providers, and additional configuration formats;
+- custom merge strategies, sequence merging, reset operators, and overlay inheritance;
+- parser-specific or custom structural-decoding extension APIs;
+- generic dynamic-subtree conversion and module-registry APIs;
+- automatic schema migrations;
+- hot reload, runtime resource replacement, and remote resource validation;
+- a bundled CLI framework or application commands; and
+- configuration diffs and fingerprints.
+
+Applications may build their own validate, effective-value, source, bootstrap, and
+explanation commands around the library. Broadening these boundaries requires
+concrete consumer evidence, compatibility review, and an explicit design change.

docs/roadmap/release-readiness.md

@@ -1,25 +0,0 @@
-# Release Readiness
-
-## Status and ownership
-
-ConfigKit is not release-ready. This document tracks outstanding release
-prerequisites under the [temporary bootstrap exception](../policy/release.md#temporary-bootstrap-deferral).
-It is not the library implementation plan and does not assign implementation
-stages. The maintainer preparing the first release owns closure.
-
-## Outstanding prerequisites
-
-| Gap | Evidence required to close |
-| --- | --- |
-| No Go module or declared support matrix | Established module path, supported Go versions and platform targets documented in the release procedure |
-| No release runbook | `docs/release.md` exists with the prerequisites, commands, publication guards, and verification required by release policy |
-| No complete release checker | A documented command exists and exercises every applicable automated candidate gate; manual gates and inapplicable checks are explicit |
-| No consumer verification procedure | Runbook verifies retrieval of the exact released module version and a representative consumer build without local replacement directives |
-| No verified secret/precedence/explanation contracts | Current contracts and passing bootstrap skip/partial-failure, secret isolation, CLI precedence, and safe historical-value regressions; representative consumer examples |
-| No validated release candidate | Version-matched release note, current contracts/examples, and complete checks against the exact committed candidate |
-
-No release can proceed while these prerequisites remain open. Close items only
-on evidence from actual files and checks, not proposed commands. Record closure
-evidence here while this roadmap remains active. Once all gaps are closed,
-remove the bootstrap exception and retire this document in favor of the
-operational runbook and normal release records.

documentation_test.go

@@ -0,0 +1,151 @@
+package configkit
+
+import (
+	"bufio"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+	"unicode"
+)
+
+var markdownLinkPattern = regexp.MustCompile(`(?m)(?:^|[[:space:]])\[[^\]]*\]\(([^)[:space:]]+)`)
+
+func TestLocalDocumentationLinks(t *testing.T) {
+	repository, err := filepath.Abs(".")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var failures []string
+	err = filepath.WalkDir(repository, func(path string, entry os.DirEntry, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+		if entry.IsDir() {
+			if entry.Name() == ".git" {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if filepath.Ext(path) != ".md" {
+			return nil
+		}
+		content, readErr := os.ReadFile(path)
+		if readErr != nil {
+			return readErr
+		}
+		for _, match := range markdownLinkPattern.FindAllStringSubmatch(string(content), -1) {
+			target := strings.Trim(match[1], "<>")
+			if strings.Contains(target, "://") || strings.HasPrefix(target, "mailto:") {
+				continue
+			}
+			filePart, fragment, _ := strings.Cut(target, "#")
+			decoded, decodeErr := url.PathUnescape(filePart)
+			if decodeErr != nil {
+				failures = append(failures, fmt.Sprintf("%s: invalid escaped link %q", relativePath(repository, path), target))
+				continue
+			}
+			linked := path
+			if decoded != "" {
+				linked = filepath.Clean(filepath.Join(filepath.Dir(path), filepath.FromSlash(decoded)))
+			}
+			_, statErr := os.Stat(linked)
+			outside := linked != repository && !strings.HasPrefix(linked, repository+string(filepath.Separator))
+			if os.IsNotExist(statErr) && outside && optionalSiblingSource(repository, linked) {
+				continue // Recorded sibling-source links are optional in isolated clones.
+			}
+			if statErr != nil {
+				failures = append(failures, fmt.Sprintf("%s: missing local link %q", relativePath(repository, path), target))
+				continue
+			}
+			if fragment != "" && filepath.Ext(linked) == ".md" && !markdownHasFragment(linked, fragment) {
+				failures = append(failures, fmt.Sprintf("%s: missing fragment in %q", relativePath(repository, path), target))
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(failures) != 0 {
+		t.Fatalf("documentation link failures:\n%s", strings.Join(failures, "\n"))
+	}
+}
+
+func optionalSiblingSource(repository, linked string) bool {
+	relative, err := filepath.Rel(filepath.Dir(repository), linked)
+	if err != nil || relative == "." || filepath.IsAbs(relative) {
+		return false
+	}
+	parts := strings.Split(filepath.ToSlash(relative), "/")
+	if len(parts) == 0 {
+		return false
+	}
+	switch strings.ToLower(parts[0]) {
+	case "narratio", "notarius", "weatherreporter", "seriatim":
+		return true
+	default:
+		return false
+	}
+}
+
+func markdownHasFragment(path, wanted string) bool {
+	file, err := os.Open(path)
+	if err != nil {
+		return false
+	}
+	defer file.Close()
+	wanted, err = url.PathUnescape(wanted)
+	if err != nil {
+		return false
+	}
+	seen := make(map[string]int)
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if !strings.HasPrefix(line, "#") {
+			continue
+		}
+		heading := strings.TrimSpace(strings.TrimLeft(line, "#"))
+		base := markdownFragment(heading)
+		count := seen[base]
+		seen[base]++
+		fragment := base
+		if count > 0 {
+			fragment = fmt.Sprintf("%s-%d", base, count)
+		}
+		if fragment == wanted {
+			return true
+		}
+	}
+	return false
+}
+
+func markdownFragment(heading string) string {
+	var result strings.Builder
+	previousSpace := false
+	for _, character := range strings.ToLower(heading) {
+		switch {
+		case unicode.IsLetter(character), unicode.IsDigit(character), character == '_', character == '-':
+			result.WriteRune(character)
+			previousSpace = false
+		case unicode.IsSpace(character):
+			if result.Len() > 0 && !previousSpace {
+				result.WriteByte('-')
+				previousSpace = true
+			}
+		}
+	}
+	return strings.TrimRight(result.String(), "-")
+}
+
+func relativePath(root, path string) string {
+	relative, err := filepath.Rel(root, path)
+	if err != nil {
+		return path
+	}
+	return filepath.ToSlash(relative)
+}

example_test.go

@@ -0,0 +1,150 @@
+package configkit_test
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+func ExampleLoad() {
+	type Config struct {
+		Enabled bool `yaml:"enabled"`
+		Workers int  `yaml:"workers"`
+	}
+	result, err := configkit.Load[Config](configkit.Bytes("example.yml", []byte("enabled: true\nworkers: 3\n")))
+	fmt.Println(result.Config, err)
+	// Output: {true 3} <nil>
+}
+
+func ExampleNoSource() {
+	type Config struct {
+		Workers int `yaml:"workers"`
+	}
+	result, err := configkit.Load(configkit.NoSource(), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{Defaults: func() Config { return Config{Workers: 4} }},
+	})
+	fmt.Println(result.Config.Workers, len(result.Sources()), err)
+	// Output: 4 0 <nil>
+}
+
+func ExampleValidation_Error() {
+	type Config struct {
+		First  string `yaml:"first"`
+		Second string `yaml:"second"`
+	}
+	_, err := configkit.Load(configkit.Bytes("duplicates.yml", []byte("first: same\nsecond: same\n")), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{Validate: func(configuration *Config, validation *configkit.Validation) {
+			if configuration.First == configuration.Second {
+				validation.Error(configkit.Keys("second"), "must differ from first", configkit.Keys("first"))
+			}
+		}},
+	})
+	var loadError *configkit.LoadError
+	errors.As(err, &loadError)
+	diagnostic := loadError.Diagnostics()[0]
+	fmt.Println(diagnostic.Code, diagnostic.Path, len(diagnostic.Related))
+	// Output: validate.error /second 1
+}
+
+func ExampleVersionRule() {
+	type Config struct {
+		Version string `yaml:"version"`
+	}
+	_, err := configkit.Load(configkit.Bytes("version.yml", []byte("version: old\n")), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{Version: &configkit.VersionRule{
+			Path: configkit.Keys("version"),
+			Check: func(version configkit.Version, validation *configkit.Validation) error {
+				if version.Text != "v1" {
+					validation.Error(configkit.Keys("version"), "unsupported version; migrate using the application guide")
+				}
+				return nil
+			},
+		}},
+	})
+	var loadError *configkit.LoadError
+	errors.As(err, &loadError)
+	fmt.Println(loadError.Diagnostics()[0].Message)
+	// Output: unsupported version; migrate using the application guide
+}
+
+func ExampleResolution() {
+	type Config struct {
+		Input   int `yaml:"input"`
+		Derived int `yaml:"derived"`
+	}
+	var order []string
+	result, err := configkit.Load(configkit.Bytes("resolved.yml", []byte("input: 3\n")), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{
+			Resolve: func(configuration *Config, resolution *configkit.Resolution) error {
+				order = append(order, "resolve")
+				configkit.Default(resolution, configkit.Keys("derived"), &configuration.Derived,
+					configuration.Input*2, "derived from input", configkit.Keys("input"))
+				return nil
+			},
+			Validate: func(configuration *Config, validation *configkit.Validation) {
+				order = append(order, "validate")
+				if configuration.Derived < configuration.Input {
+					validation.Error(configkit.Keys("derived"), "must not be less than input")
+				}
+			},
+		},
+	})
+	fmt.Println(strings.Join(order, " then "), result.Config.Derived, err)
+	// Output: resolve then validate 6 <nil>
+}
+
+func ExampleSecretEnv() {
+	const name = "CONFIGKIT_EXAMPLE_API_KEY"
+	previous, present := os.LookupEnv(name)
+	_ = os.Setenv(name, "disposable-example-value")
+	defer func() {
+		if present {
+			_ = os.Setenv(name, previous)
+		} else {
+			_ = os.Unsetenv(name)
+		}
+	}()
+
+	type Config struct {
+		APIKey configkit.Secret `yaml:"api_key"`
+	}
+	result, err := configkit.Load[Config](configkit.Bytes("secret.yml", []byte("api_key: "+name+"\n")))
+	fmt.Println(result.Config.APIKey.EnvName(), result.Config.APIKey.IsResolved(), err)
+	// Output: CONFIGKIT_EXAMPLE_API_KEY true <nil>
+}
+
+func ExampleOverride() {
+	type Config struct {
+		Workers int `yaml:"workers"`
+	}
+	workers, workersWasSet := 0, true // Supplied by the application's CLI parser.
+	var overrides []configkit.Override
+	if workersWasSet {
+		overrides = append(overrides, configkit.Override{
+			Path: configkit.Keys("workers"), Value: workers, Flag: "--workers",
+		})
+	}
+	result, err := configkit.Load(configkit.NoSource(), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{Defaults: func() Config { return Config{Workers: 4} }},
+		Overrides:  overrides,
+	})
+	fmt.Println(result.Config.Workers, result.Sources()[0].Label, err)
+	// Output: 0 --workers <nil>
+}
+
+func ExampleResult_Explain() {
+	type Config struct {
+		Workers int `yaml:"workers"`
+	}
+	result, err := configkit.Load(configkit.Bytes("config.yml", []byte("workers: 8\n")), configkit.Options[Config]{
+		Definition: configkit.Definition[Config]{Defaults: func() Config { return Config{Workers: 4} }},
+	})
+	explanation, ok := result.Explain(configkit.Keys("workers"))
+	fmt.Printf("%s -> %s known=%t error=%v\n",
+		strings.TrimSpace(explanation.History[0].After.YAML),
+		strings.TrimSpace(explanation.Effective.YAML), ok, err)
+	// Output: 4 -> 8 known=true error=<nil>
+}

examples/consumers/consumers.go

@@ -0,0 +1,395 @@
+// Package consumers contains small, maintained application shapes that exercise
+// ConfigKit without making consumer domain policy part of the library API.
+package consumers
+
+import (
+	"math"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+// Artifact is a Narratio-shaped generated output declaration.
+type Artifact struct {
+	Output  string        `yaml:"output"`
+	Timeout time.Duration `yaml:"timeout"`
+}
+
+// NarratioConfig demonstrates application defaults, partial imports, and
+// application-owned model-profile and artifact semantics.
+type NarratioConfig struct {
+	PollInterval time.Duration       `yaml:"poll_interval"`
+	Timeout      time.Duration       `yaml:"timeout"`
+	ModelProfile string              `yaml:"model_profile"`
+	Artifacts    map[string]Artifact `yaml:"artifacts"`
+}
+
+// LoadNarratio loads the maintained import fixture with Narratio-shaped rules.
+func LoadNarratio(path string) (*configkit.Result[NarratioConfig], error) {
+	return LoadNarratioOverlay(path, "")
+}
+
+// LoadNarratioOverlay selects a ConfigKit configuration overlay independently
+// from the application's ModelProfile field.
+func LoadNarratioOverlay(path, overlay string) (*configkit.Result[NarratioConfig], error) {
+	return configkit.Load(configkit.File(path), configkit.Options[NarratioConfig]{
+		Imports: true, Overlay: overlay,
+		Definition: configkit.Definition[NarratioConfig]{
+			Defaults: func() NarratioConfig { return NarratioConfig{PollInterval: time.Minute} },
+			Resolve:  resolveNarratio,
+			Validate: validateNarratio,
+		},
+	})
+}
+
+func resolveNarratio(configuration *NarratioConfig, resolution *configkit.Resolution) error {
+	configkit.Default(resolution, configkit.Keys("timeout"), &configuration.Timeout,
+		configuration.PollInterval/10, "derived from poll interval", configkit.Keys("poll_interval"))
+	for name, artifact := range configuration.Artifacts {
+		path := configkit.Keys("artifacts", name)
+		configkit.Default(resolution, path.Key("timeout"), &artifact.Timeout,
+			configuration.Timeout, "inherited pipeline timeout", configkit.Keys("timeout"))
+		configkit.Normalize(resolution, path.Key("output"), &artifact.Output,
+			strings.TrimSpace(artifact.Output), "trimmed artifact output")
+		configuration.Artifacts[name] = artifact
+	}
+	return nil
+}
+
+func validateNarratio(configuration *NarratioConfig, validation *configkit.Validation) {
+	if configuration.PollInterval <= 0 {
+		validation.Error(configkit.Keys("poll_interval"), "must be positive")
+	}
+	if configuration.Timeout <= 0 {
+		validation.Error(configkit.Keys("timeout"), "must be positive")
+	}
+	for name, artifact := range configuration.Artifacts {
+		path := configkit.Keys("artifacts", name)
+		if artifact.Output == "" {
+			validation.Error(path.Key("output"), "must be nonempty")
+		}
+		if artifact.Timeout <= 0 {
+			validation.Error(path.Key("timeout"), "must be positive")
+		}
+	}
+}
+
+// ObjectBinding is a Notarius-shaped canonical object binding. Options remain
+// dynamic because the application catalog selects their schema at runtime.
+type ObjectBinding struct {
+	Object  string         `yaml:"object"`
+	Options map[string]any `yaml:"options"`
+}
+
+// NotariusConfig demonstrates string-backed versions and dynamic catalog options.
+type NotariusConfig struct {
+	Version  string          `yaml:"version"`
+	Bindings []ObjectBinding `yaml:"bindings"`
+}
+
+// LoadNotarius loads a Notarius-shaped configuration.
+func LoadNotarius(path string) (*configkit.Result[NotariusConfig], error) {
+	return configkit.Load(configkit.File(path), configkit.Options[NotariusConfig]{
+		Definition: configkit.Definition[NotariusConfig]{
+			Version:  &configkit.VersionRule{Path: configkit.Keys("version"), Check: requireVersion("4")},
+			Validate: validateNotarius,
+		},
+	})
+}
+
+func requireVersion(expected string) func(configkit.Version, *configkit.Validation) error {
+	return func(version configkit.Version, validation *configkit.Validation) error {
+		if !version.Present || version.Null || version.Text != expected {
+			validation.Error(configkit.Keys("version"), "unsupported configuration version")
+		}
+		return nil
+	}
+}
+
+func validateNotarius(configuration *NotariusConfig, validation *configkit.Validation) {
+	for index, binding := range configuration.Bindings {
+		path := configkit.Keys("bindings").Index(index)
+		if binding.Object != "summary" && binding.Object != "registry" {
+			validation.Error(path.Key("object"), "unsupported object binding")
+		}
+		for key, value := range binding.Options {
+			optionPath := path.Key("options").Key(key)
+			switch key {
+			case "window_units":
+				units, ok := value.(int64)
+				if !ok || units < 1 {
+					validation.Error(optionPath, "must be a positive integer")
+				}
+			case "format":
+				if _, ok := value.(string); !ok {
+					validation.Error(optionPath, "must be a string")
+				}
+			default:
+				validation.Error(optionPath, "unsupported object option")
+			}
+		}
+	}
+}
+
+// NotariusWindow converts ConfigKit's portable dynamic integer only at the
+// application runtime boundary.
+func NotariusWindow(configuration NotariusConfig, binding int) (int, bool) {
+	if binding < 0 || binding >= len(configuration.Bindings) {
+		return 0, false
+	}
+	value, ok := configuration.Bindings[binding].Options["window_units"].(int64)
+	if !ok || value < 1 || (strconv.IntSize == 32 && value > math.MaxInt32) {
+		return 0, false
+	}
+	return int(value), true
+}
+
+// NotariusPathConfig demonstrates application-owned interpretation of a
+// path-valued configuration field. ConfigKit supplies provenance; this example
+// selects its own relative-path bases.
+type NotariusPathConfig struct {
+	Reference string `yaml:"reference"`
+	Sensitive string `yaml:"sensitive"`
+}
+
+// LoadNotariusPaths loads the path-bearing Notarius-shaped example. InvocationDir
+// is the application-supplied base for relative CLI overrides; it is never read
+// from the process working directory.
+func LoadNotariusPaths(path, invocationDir string, overrides ...configkit.Override) (*configkit.Result[NotariusPathConfig], error) {
+	return configkit.Load(configkit.File(path), configkit.Options[NotariusPathConfig]{
+		Imports: true, Overrides: overrides,
+		Definition: configkit.Definition[NotariusPathConfig]{
+			Defaults: func() NotariusPathConfig { return NotariusPathConfig{Reference: "defaults/reference.txt"} },
+			Resolve: func(configuration *NotariusPathConfig, resolution *configkit.Resolution) error {
+				resolveNotariusReference(configuration, resolution, invocationDir)
+				return nil
+			},
+			Secret: func(path configkit.Path) bool { return path.String() == "/sensitive" },
+		},
+	})
+}
+
+func resolveNotariusReference(configuration *NotariusPathConfig, resolution *configkit.Resolution, invocationDir string) {
+	path := configkit.Keys("reference")
+	if configuration.Reference == "" || filepath.IsAbs(configuration.Reference) {
+		return
+	}
+	info, found := resolution.InputInfo(path)
+	if !found {
+		resolution.Warning(path, "relative reference has no entry provenance")
+		return
+	}
+
+	base := ""
+	if info.Origin.Layer == configkit.LayerCLI {
+		base = invocationDir
+		if base == "" {
+			resolution.Warning(path, "relative CLI reference has no invocation directory")
+			return
+		}
+	} else {
+		sourceID := "source-1" // ConfigKit's primary-source identity convention.
+		if info.Origin.Layer != configkit.LayerDefault {
+			if len(info.Origin.Locations) != 1 {
+				resolution.Warning(path, "relative reference has no unambiguous declaring source")
+				return
+			}
+			sourceID = info.Origin.Locations[0].SourceID
+		}
+		source, exists := resolution.Source(sourceID)
+		if !exists || source.Path == "" {
+			resolution.Warning(path, "relative reference has no declaring file")
+			return
+		}
+		base = filepath.Dir(source.Path)
+	}
+	configkit.Normalize(resolution, path, &configuration.Reference,
+		filepath.Join(base, configuration.Reference), "resolved relative reference from entry source")
+}
+
+// ModuleOptions is a WeatherReporter-shaped union of known module option fields.
+type ModuleOptions struct {
+	WindowUnits *int     `yaml:"window_units"`
+	Sections    []string `yaml:"sections"`
+}
+
+// ModuleSpec uses the canonical object form instead of a string shorthand.
+type ModuleSpec struct {
+	Module  string        `yaml:"module"`
+	Options ModuleOptions `yaml:"options"`
+}
+
+// ReportConfig keeps report-specific lists application-owned.
+type ReportConfig struct {
+	Modules       []ModuleSpec `yaml:"modules"`
+	PathTemplates []string     `yaml:"path_templates"`
+}
+
+// WeatherConfig demonstrates simple defaults, reports, module options, and an
+// optional typed secret reference.
+type WeatherConfig struct {
+	Units   string                  `yaml:"units"`
+	Reports map[string]ReportConfig `yaml:"reports"`
+	Token   *configkit.Secret       `yaml:"token"`
+}
+
+// LoadWeather loads a WeatherReporter-shaped source and explicit CLI records.
+func LoadWeather(source configkit.Source, overrides ...configkit.Override) (*configkit.Result[WeatherConfig], error) {
+	return configkit.Load(source, configkit.Options[WeatherConfig]{
+		Overrides: overrides,
+		Definition: weatherDefinition(func() WeatherConfig {
+			return WeatherConfig{Units: "metric"}
+		}),
+	})
+}
+
+// LoadConstructedWeather runs the same rules over a detached constructed value.
+func LoadConstructedWeather(configuration WeatherConfig) (*configkit.Result[WeatherConfig], error) {
+	return configkit.Load(configkit.NoSource(), configkit.Options[WeatherConfig]{
+		Definition: weatherDefinition(func() WeatherConfig { return configuration }),
+	})
+}
+
+func weatherDefinition(defaults func() WeatherConfig) configkit.Definition[WeatherConfig] {
+	return configkit.Definition[WeatherConfig]{
+		Defaults: defaults,
+		Resolve: func(configuration *WeatherConfig, resolution *configkit.Resolution) error {
+			for reportName, report := range configuration.Reports {
+				var modules []ModuleSpec
+				if report.Modules != nil {
+					modules = append(make([]ModuleSpec, 0, len(report.Modules)), report.Modules...)
+				}
+				for index, module := range modules {
+					if module.Options.Sections != nil {
+						sections := append([]string(nil), module.Options.Sections...)
+						for position := range sections {
+							sections[position] = strings.TrimSpace(sections[position])
+						}
+						module.Options.Sections = sections
+					}
+					modules[index] = module
+				}
+				configkit.Normalize(resolution, configkit.Keys("reports", reportName, "modules"),
+					&report.Modules, modules, "normalized module options")
+				configuration.Reports[reportName] = report
+			}
+			return nil
+		},
+		Validate: validateWeather,
+	}
+}
+
+func validateWeather(configuration *WeatherConfig, validation *configkit.Validation) {
+	if configuration.Units != "metric" && configuration.Units != "us" {
+		validation.Error(configkit.Keys("units"), "must be metric or us")
+	}
+	for reportName, report := range configuration.Reports {
+		path := configkit.Keys("reports", reportName)
+		if report.Modules != nil && len(report.Modules) == 0 {
+			validation.Error(path.Key("modules"), "must contain at least one module")
+		}
+		if report.PathTemplates != nil && len(report.PathTemplates) == 0 {
+			validation.Error(path.Key("path_templates"), "must contain at least one template")
+		}
+		for index, module := range report.Modules {
+			modulePath := path.Key("modules").Index(index)
+			switch module.Module {
+			case "chunker":
+				if module.Options.WindowUnits == nil || *module.Options.WindowUnits < 1 {
+					validation.Error(modulePath.Key("options").Key("window_units"), "must be a positive integer")
+				}
+				if module.Options.Sections != nil {
+					validation.Error(modulePath.Key("options").Key("sections"), "not supported by this module")
+				}
+			case "discussion":
+				if module.Options.WindowUnits != nil {
+					validation.Error(modulePath.Key("options").Key("window_units"), "not supported by this module")
+				}
+				if len(module.Options.Sections) == 0 {
+					validation.Error(modulePath.Key("options").Key("sections"), "must contain at least one section")
+				}
+			default:
+				validation.Error(modulePath.Key("module"), "unsupported module")
+			}
+		}
+	}
+}
+
+// SpeakerRule and SpeakerRules preserve declaration order for application matching.
+type SpeakerRule struct {
+	Prefix string `yaml:"prefix"`
+	Name   string `yaml:"name"`
+}
+
+type SpeakerRules struct {
+	Rules []SpeakerRule `yaml:"rules"`
+}
+
+// AutocorrectRule and AutocorrectRules preserve replacement order.
+type AutocorrectRule struct {
+	Find    string `yaml:"find"`
+	Replace string `yaml:"replace"`
+}
+
+type AutocorrectRules struct {
+	Rules []AutocorrectRule `yaml:"rules"`
+}
+
+// LoadSpeakerRules loads one independent Seriatim-shaped rule file.
+func LoadSpeakerRules(path string) (*configkit.Result[SpeakerRules], error) {
+	return configkit.Load(configkit.File(path), configkit.Options[SpeakerRules]{
+		Definition: configkit.Definition[SpeakerRules]{Validate: validateSpeakerRules},
+	})
+}
+
+// LoadAutocorrectRules loads another independent ordered rule file.
+func LoadAutocorrectRules(path string) (*configkit.Result[AutocorrectRules], error) {
+	return configkit.Load(configkit.File(path), configkit.Options[AutocorrectRules]{
+		Definition: configkit.Definition[AutocorrectRules]{Validate: validateAutocorrectRules},
+	})
+}
+
+func validateSpeakerRules(configuration *SpeakerRules, validation *configkit.Validation) {
+	seen := make(map[string]int)
+	for index, rule := range configuration.Rules {
+		path := configkit.Keys("rules").Index(index)
+		if rule.Prefix == "" {
+			validation.Error(path.Key("prefix"), "must be nonempty")
+		}
+		if previous, ok := seen[rule.Prefix]; ok {
+			validation.Error(path.Key("prefix"), "prefix must be unique",
+				configkit.Keys("rules").Index(previous).Key("prefix"))
+		}
+		seen[rule.Prefix] = index
+	}
+}
+
+func validateAutocorrectRules(configuration *AutocorrectRules, validation *configkit.Validation) {
+	for index, rule := range configuration.Rules {
+		path := configkit.Keys("rules").Index(index)
+		if rule.Find == "" {
+			validation.Error(path.Key("find"), "must be nonempty")
+		}
+	}
+}
+
+// SpeakerName is application runtime matching, not configuration infrastructure.
+func SpeakerName(rules SpeakerRules, input string) (string, bool) {
+	for _, rule := range rules.Rules {
+		if strings.HasPrefix(input, rule.Prefix) {
+			return rule.Name, true
+		}
+	}
+	return "", false
+}
+
+// ApplyAutocorrect is application runtime replacement in declared order.
+func ApplyAutocorrect(rules AutocorrectRules, input string) string {
+	for _, rule := range rules.Rules {
+		input = strings.ReplaceAll(input, rule.Find, rule.Replace)
+	}
+	return input
+}

examples/consumers/consumers_test.go

@@ -0,0 +1,353 @@
+package consumers_test
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+	"gitea.maximumdirect.net/eric/ConfigKit/examples/consumers"
+)
+
+func Example_narratio() {
+	result, err := consumers.LoadNarratio(fixture("narratio", "pipeline.yml"))
+	artifact := result.Config.Artifacts["transcript"]
+	fmt.Println(result.Config.ModelProfile, artifact.Output, result.Config.Timeout, artifact.Timeout, err)
+	// Output: concise transcript.txt 6s 6s <nil>
+}
+
+func Example_notarius() {
+	result, err := consumers.LoadNotarius(fixture("notarius", "config.yml"))
+	window, ok := consumers.NotariusWindow(result.Config, 0)
+	fmt.Println(result.Config.Version, result.Config.Bindings[0].Object, window, ok, err)
+	// Output: 4 summary 12 true <nil>
+}
+
+func Example_notariusPaths() {
+	result, err := consumers.LoadNotariusPaths(fixture("notarius-paths", "main.yml"), "/invocation")
+	fmt.Println(filepath.Base(result.Config.Reference), err)
+	// Output: imported.txt <nil>
+}
+
+func Example_weatherReporter() {
+	defaults, defaultsErr := consumers.LoadWeather(configkit.NoSource())
+	result, err := consumers.LoadWeather(configkit.File(fixture("weather", "config.yml")))
+	discussion := result.Config.Reports["daily"].Modules[1]
+	fmt.Println(defaults.Config.Units, result.Config.Units, discussion.Options.Sections[0], defaultsErr, err)
+	// Output: metric us short_term <nil> <nil>
+}
+
+func Example_seriatim() {
+	speakers, speakerErr := consumers.LoadSpeakerRules(fixture("seriatim", "speakers.yml"))
+	autocorrect, autocorrectErr := consumers.LoadAutocorrectRules(fixture("seriatim", "autocorrect.yml"))
+	name, found := consumers.SpeakerName(speakers.Config, "Guest: teh event occured")
+	text := consumers.ApplyAutocorrect(autocorrect.Config, "teh event occured")
+	fmt.Println(name, found, text, speakerErr, autocorrectErr)
+	// Output: visitor true the event occurred <nil> <nil>
+}
+
+func Example_weatherStartup() {
+	const blockedName = "CONFIGKIT_WEATHER_EXAMPLE_BLOCKED"
+	const tokenName = "CONFIGKIT_WEATHER_EXAMPLE_TOKEN"
+	restoreBlocked := preserveEnvironment(blockedName)
+	restoreToken := preserveEnvironment(tokenName)
+	defer restoreBlocked()
+	defer restoreToken()
+	_ = os.Setenv(blockedName, "")
+	_ = os.Unsetenv(tokenName)
+
+	directory, _ := os.MkdirTemp("", "configkit-weather-example-")
+	defer os.RemoveAll(directory)
+	_ = os.WriteFile(filepath.Join(directory, blockedName), []byte("unused-example-value\n"), 0o600)
+	_ = os.WriteFile(filepath.Join(directory, tokenName), []byte("disposable-example-credential\n"), 0o600)
+	report, bootstrapErr := configkit.LoadSecretsDir(directory)
+	var reportOutput bytes.Buffer
+	_, reportWriteErr := report.WriteTo(&reportOutput)
+
+	result, loadErr := consumers.LoadWeather(configkit.Bytes("weather.yml", []byte("units: metric\ntoken: "+tokenName+"\n")),
+		configkit.Override{Path: configkit.Keys("units"), Value: "us", Flag: "--units"})
+	var explanation bytes.Buffer
+	explainErr := result.WriteExplanation(&explanation, configkit.Keys("units"))
+	blocked, loaded := secretStatus(report, blockedName), secretStatus(report, tokenName)
+	value, present := os.LookupEnv(tokenName)
+	fmt.Printf("blocked=%s loaded=%s report=%t reference=%s explained=%t unchanged=%t errors=%t\n",
+		blocked, loaded, reportOutput.Len() > 0, result.Config.Token.EnvName(),
+		strings.Contains(explanation.String(), "--units"), present && value == "disposable-example-credential",
+		bootstrapErr != nil || reportWriteErr != nil || loadErr != nil || explainErr != nil)
+	// Output: blocked=skipped_existing loaded=loaded report=true reference=CONFIGKIT_WEATHER_EXAMPLE_TOKEN explained=true unchanged=true errors=false
+}
+
+func TestMaintainedConsumerFixturesPreserveDomainOutcomes(t *testing.T) {
+	narratio, err := consumers.LoadNarratio(fixture("narratio", "pipeline.yml"))
+	if err != nil || narratio.Config.Artifacts["transcript"].Output != "transcript.txt" ||
+		narratio.Config.ModelProfile != "concise" || len(narratio.Sources()) != 2 {
+		t.Fatalf("Narratio shape = %#v, %v", narratio, err)
+	}
+	if origin, ok := narratio.Metadata().Lookup(configkit.Keys("artifacts", "transcript", "output")); !ok || origin.Origin.Layer != configkit.LayerResolution {
+		t.Fatalf("artifact origin = %#v, %v", origin, ok)
+	}
+	overlaid, err := consumers.LoadNarratioOverlay(fixture("narratio", "pipeline.yml"), "testing")
+	if err != nil || overlaid.Config.PollInterval.String() != "2m0s" ||
+		overlaid.Config.ModelProfile != "concise" || len(overlaid.Sources()) != 3 {
+		t.Fatalf("configuration overlay and application model profile = %#v, %v", overlaid, err)
+	}
+	if source := overlaid.Sources()[2]; source.Label != "overlays/testing.yml" || source.Layer != configkit.LayerOverlay {
+		t.Fatalf("Narratio overlay source = %#v", source)
+	}
+
+	notarius, err := consumers.LoadNotarius(fixture("notarius", "config.yml"))
+	window, converted := consumers.NotariusWindow(notarius.Config, 0)
+	if err != nil || !converted || window != 12 {
+		t.Fatalf("Notarius shape = %#v, %v, %v", notarius, converted, err)
+	}
+	if _, ok := notarius.Config.Bindings[0].Options["window_units"].(int64); !ok {
+		t.Fatalf("dynamic integer type = %T", notarius.Config.Bindings[0].Options["window_units"])
+	}
+	integerNotarius, err := consumers.LoadNotarius(fixture("notarius", "integer-version.yml"))
+	if err != nil || integerNotarius.Config.Version != notarius.Config.Version || integerNotarius.Config.Version != "4" {
+		t.Fatalf("Notarius version forms = %#v / %#v, %v", notarius.Config, integerNotarius, err)
+	}
+
+	weather, err := consumers.LoadWeather(configkit.File(fixture("weather", "config.yml")))
+	if err != nil || weather.Config.Reports["daily"].Modules[1].Options.Sections[0] != "short_term" {
+		t.Fatalf("WeatherReporter shape = %#v, %v", weather, err)
+	}
+
+	speakers, err := consumers.LoadSpeakerRules(fixture("seriatim", "speakers.yml"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	name, ok := consumers.SpeakerName(speakers.Config, "Host: introduction")
+	if !ok || name != "narrator" || speakers.Config.Rules[0].Prefix != "Host:" {
+		t.Fatalf("ordered speaker rules = %#v, %q, %v", speakers.Config.Rules, name, ok)
+	}
+}
+
+func TestMigrationFixturesFailWithStableCodesAndPaths(t *testing.T) {
+	tests := []struct {
+		name string
+		load func() error
+		code configkit.Code
+		path string
+	}{
+		{
+			name: "unsupported application version",
+			load: func() error {
+				_, err := consumers.LoadNotarius(fixture("notarius", "unsupported-version.yml"))
+				return err
+			},
+			code: configkit.CodeVersionError, path: "/version",
+		},
+		{
+			name: "non-integer numeric version",
+			load: func() error {
+				_, err := consumers.LoadNotarius(fixture("notarius", "noninteger-version.yml"))
+				return err
+			},
+			code: configkit.CodeVersionType, path: "/version",
+		},
+		{
+			name: "module shorthand",
+			load: func() error {
+				_, err := consumers.LoadWeather(configkit.File(fixture("weather", "shorthand-module.yml")))
+				return err
+			},
+			code: configkit.CodeDecodeType, path: "/reports/daily/modules/0",
+		},
+		{
+			name: "explicit empty modules",
+			load: func() error {
+				_, err := consumers.LoadWeather(configkit.File(fixture("weather", "empty-modules.yml")))
+				return err
+			},
+			code: configkit.CodeValidateError, path: "/reports/daily/modules",
+		},
+		{
+			name: "explicit empty path templates",
+			load: func() error {
+				_, err := consumers.LoadWeather(configkit.File(fixture("weather", "empty-paths.yml")))
+				return err
+			},
+			code: configkit.CodeValidateError, path: "/reports/daily/path_templates",
+		},
+		{
+			name: "explicit null required option",
+			load: func() error {
+				_, err := consumers.LoadWeather(configkit.File(fixture("weather", "null-window.yml")))
+				return err
+			},
+			code: configkit.CodeValidateError, path: "/reports/daily/modules/0/options/window_units",
+		},
+		{
+			name: "strict unknown rule field",
+			load: func() error {
+				_, err := consumers.LoadSpeakerRules(fixture("seriatim", "unknown-field.yml"))
+				return err
+			},
+			code: configkit.CodeDecodeUnknownField, path: "/rules/0/color",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var loadError *configkit.LoadError
+			if err := test.load(); !errors.As(err, &loadError) {
+				t.Fatalf("error = %T %v", err, err)
+			}
+			diagnostics := loadError.Diagnostics()
+			if len(diagnostics) == 0 || diagnostics[0].Code != test.code || diagnostics[0].Path.String() != test.path {
+				t.Fatalf("diagnostics = %#v", diagnostics)
+			}
+			if strings.Contains(diagnostics[0].Message, "wrong-before-overlay") {
+				t.Fatalf("diagnostic exposed raw parser input: %#v", diagnostics[0])
+			}
+		})
+	}
+}
+
+func TestWeatherLoadedAndConstructedRulesAgreeWithoutMutation(t *testing.T) {
+	loaded, err := consumers.LoadWeather(configkit.File(fixture("weather", "config.yml")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	reconstructed, err := consumers.LoadConstructedWeather(loaded.Config)
+	if err != nil || !reflect.DeepEqual(reconstructed.Config, loaded.Config) {
+		t.Fatalf("loaded/constructed outcomes differ: %#v, %v", reconstructed, err)
+	}
+	constructed := consumers.WeatherConfig{Units: loaded.Config.Units, Reports: map[string]consumers.ReportConfig{}}
+	constructed.Reports["daily"] = consumers.ReportConfig{
+		Modules:       []consumers.ModuleSpec{{Module: "discussion", Options: consumers.ModuleOptions{Sections: []string{" short_term "}}}},
+		PathTemplates: []string{"daily/{date}.md"},
+	}
+	wantInput := constructed.Reports["daily"].Modules[0].Options.Sections[0]
+	result, err := consumers.LoadConstructedWeather(constructed)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := constructed.Reports["daily"].Modules[0].Options.Sections[0]; got != wantInput {
+		t.Fatalf("constructed options mutated from %q to %q", wantInput, got)
+	}
+	if result.Config.Reports["daily"].Modules[0].Options.Sections[0] != "short_term" {
+		t.Fatalf("normalized result = %#v", result.Config.Reports["daily"])
+	}
+
+	empty := consumers.WeatherConfig{Units: "metric", Reports: map[string]consumers.ReportConfig{
+		"daily": {Modules: []consumers.ModuleSpec{}},
+	}}
+	_, err = consumers.LoadConstructedWeather(empty)
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) || loadError.Diagnostics()[0].Code != configkit.CodeValidateError {
+		t.Fatalf("constructed empty modules error = %v", err)
+	}
+	if !reflect.DeepEqual(empty.Reports["daily"].Modules, []consumers.ModuleSpec{}) {
+		t.Fatal("constructed empty module input was mutated")
+	}
+}
+
+func TestNotariusPathExampleUsesEntryProvenance(t *testing.T) {
+	main := fixture("notarius-paths", "main.yml")
+	declared := fixture("notarius-paths", "declarations", "path.yml")
+	declaredCanonical := canonicalFixture(t, declared)
+	wantImported := filepath.Join(filepath.Dir(declaredCanonical), "..", "assets", "imported.txt")
+	result, err := consumers.LoadNotariusPaths(main, filepath.Join(t.TempDir(), "invocation"))
+	if err != nil || result.Config.Reference != wantImported {
+		t.Fatalf("imported reference = %#v, %v", result, err)
+	}
+	var effective bytes.Buffer
+	if err := result.WriteEffective(&effective); err != nil || !strings.Contains(effective.String(), wantImported) ||
+		strings.Contains(effective.String(), "PATH_REFERENCE_SECRET_CANARY") {
+		t.Fatalf("effective output = %q, %v", effective.String(), err)
+	}
+	explanation, found := result.Explain(configkit.Keys("reference"))
+	if !found || len(explanation.History) == 0 || explanation.History[len(explanation.History)-1].Before.YAML != "../assets/imported.txt\n" ||
+		len(explanation.History[len(explanation.History)-1].Reasons) != 1 || explanation.History[len(explanation.History)-1].Reasons[0] != "resolved relative reference from entry source" {
+		t.Fatalf("reference explanation = %#v, %v", explanation, found)
+	}
+	sensitive, found := result.Explain(configkit.Keys("sensitive"))
+	var rendered bytes.Buffer
+	writeErr := result.WriteExplanation(&rendered, configkit.Keys("sensitive"))
+	if !found || !sensitive.Effective.Redacted || writeErr != nil ||
+		strings.Contains(fmt.Sprintf("%#v %s", sensitive, rendered.String()), "PATH_REFERENCE_SECRET_CANARY") {
+		t.Fatalf("sensitive inspection = %#v, %q, %v", sensitive, rendered.String(), writeErr)
+	}
+
+	defaults := fixture("notarius-paths", "defaults.yml")
+	defaultCanonical := canonicalFixture(t, defaults)
+	defaultResult, err := consumers.LoadNotariusPaths(defaults, filepath.Join(t.TempDir(), "invocation"))
+	wantDefault := filepath.Join(filepath.Dir(defaultCanonical), "defaults", "reference.txt")
+	if err != nil || defaultResult.Config.Reference != wantDefault {
+		t.Fatalf("default reference = %#v, %v", defaultResult, err)
+	}
+
+	invocation := filepath.Join(t.TempDir(), "caller")
+	cliResult, err := consumers.LoadNotariusPaths(main, invocation,
+		configkit.Override{Path: configkit.Keys("reference"), Value: "cli/reference.txt", Flag: "--reference"})
+	wantCLI := filepath.Join(invocation, "cli", "reference.txt")
+	if err != nil || cliResult.Config.Reference != wantCLI {
+		t.Fatalf("CLI reference = %#v, %v", cliResult, err)
+	}
+	missingBase, err := consumers.LoadNotariusPaths(main, "",
+		configkit.Override{Path: configkit.Keys("reference"), Value: "cli/reference.txt", Flag: "--reference"})
+	if err != nil || missingBase.Config.Reference != "cli/reference.txt" || len(missingBase.Diagnostics()) != 1 ||
+		missingBase.Diagnostics()[0].Code != configkit.CodeResolveWarning {
+		t.Fatalf("missing CLI base = %#v, %v", missingBase, err)
+	}
+	absolute := filepath.Join(t.TempDir(), "absolute.txt")
+	absoluteResult, err := consumers.LoadNotariusPaths(main, invocation,
+		configkit.Override{Path: configkit.Keys("reference"), Value: absolute, Flag: "--reference"})
+	if err != nil || absoluteResult.Config.Reference != absolute {
+		t.Fatalf("absolute reference = %#v, %v", absoluteResult, err)
+	}
+
+	target := fixture("notarius-paths", "symlink-target.yml")
+	link := filepath.Join(t.TempDir(), "linked-config.yml")
+	if err := os.Symlink(target, link); err != nil {
+		t.Skipf("symlink fixture unavailable: %v", err)
+	}
+	symlinkResult, err := consumers.LoadNotariusPaths(link, invocation)
+	targetCanonical := canonicalFixture(t, target)
+	wantSymlink := filepath.Join(filepath.Dir(targetCanonical), "..", "assets", "target.txt")
+	if err != nil || symlinkResult.Config.Reference != wantSymlink {
+		t.Fatalf("symlink reference = %#v, %v", symlinkResult, err)
+	}
+}
+
+func fixture(parts ...string) string {
+	_, file, _, _ := runtime.Caller(0)
+	values := append([]string{filepath.Dir(file), "testdata"}, parts...)
+	return filepath.Join(values...)
+}
+
+func canonicalFixture(t *testing.T, path string) string {
+	t.Helper()
+	canonical, err := filepath.EvalSymlinks(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return canonical
+}
+
+func preserveEnvironment(name string) func() {
+	value, present := os.LookupEnv(name)
+	return func() {
+		if present {
+			_ = os.Setenv(name, value)
+		} else {
+			_ = os.Unsetenv(name)
+		}
+	}
+}
+
+func secretStatus(report *configkit.SecretsReport, name string) configkit.SecretFileStatus {
+	for _, entry := range report.Entries() {
+		if entry.Name == name {
+			return entry.Status
+		}
+	}
+	return "missing"
+}

examples/consumers/testdata/narratio/artifacts.yml

@@ -0,0 +1,3 @@
+artifacts:
+  transcript:
+    output: ' transcript.txt '

examples/consumers/testdata/narratio/overlays/testing.yml

@@ -0,0 +1 @@
+poll_interval: 2m

examples/consumers/testdata/narratio/pipeline.yml

@@ -0,0 +1,5 @@
+configkit:
+  imports:
+    - path: artifacts.yml
+poll_interval: 1m
+model_profile: concise

examples/consumers/testdata/notarius-paths/declarations/path.yml

@@ -0,0 +1 @@
+reference: ../assets/imported.txt

examples/consumers/testdata/notarius-paths/defaults.yml

@@ -0,0 +1 @@
+sensitive: PATH_REFERENCE_SECRET_CANARY

examples/consumers/testdata/notarius-paths/main.yml

@@ -0,0 +1,4 @@
+configkit:
+  imports:
+    - path: declarations/path.yml
+sensitive: PATH_REFERENCE_SECRET_CANARY

examples/consumers/testdata/notarius-paths/symlink-target.yml

@@ -0,0 +1,2 @@
+reference: ../assets/target.txt
+sensitive: PATH_REFERENCE_SECRET_CANARY

examples/consumers/testdata/notarius/config.yml

@@ -0,0 +1,6 @@
+version: "4"
+bindings:
+  - object: summary
+    options:
+      window_units: 12
+      format: markdown

examples/consumers/testdata/notarius/integer-version.yml

@@ -0,0 +1,6 @@
+version: 4
+bindings:
+  - object: summary
+    options:
+      window_units: 12
+      format: markdown

examples/consumers/testdata/notarius/noninteger-version.yml

@@ -0,0 +1,2 @@
+version: 4.0
+bindings: []

examples/consumers/testdata/notarius/unsupported-version.yml

@@ -0,0 +1,2 @@
+version: 5
+bindings: []

examples/consumers/testdata/seriatim/autocorrect.yml

@@ -0,0 +1,5 @@
+rules:
+  - find: teh
+    replace: the
+  - find: occured
+    replace: occurred

examples/consumers/testdata/seriatim/speakers.yml

@@ -0,0 +1,5 @@
+rules:
+  - prefix: 'Host:'
+    name: narrator
+  - prefix: 'Guest:'
+    name: visitor

examples/consumers/testdata/seriatim/unknown-field.yml

@@ -0,0 +1,4 @@
+rules:
+  - prefix: 'Host:'
+    name: narrator
+    color: blue

examples/consumers/testdata/weather/config.yml

@@ -0,0 +1,11 @@
+units: us
+reports:
+  daily:
+    modules:
+      - module: chunker
+        options:
+          window_units: 12
+      - module: discussion
+        options:
+          sections: [' short_term ']
+    path_templates: ['daily/{date}.md']

examples/consumers/testdata/weather/empty-modules.yml

@@ -0,0 +1,3 @@
+reports:
+  daily:
+    modules: []

examples/consumers/testdata/weather/empty-paths.yml

@@ -0,0 +1,3 @@
+reports:
+  daily:
+    path_templates: []

examples/consumers/testdata/weather/null-window.yml

@@ -0,0 +1,6 @@
+reports:
+  daily:
+    modules:
+      - module: chunker
+        options:
+          window_units: null

examples/consumers/testdata/weather/shorthand-module.yml

@@ -0,0 +1,3 @@
+reports:
+  daily:
+    modules: [chunker]

facade_candidate_test.go

@@ -0,0 +1,272 @@
+package configkit_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+var (
+	_ error          = (*configkit.LoadError)(nil)
+	_ fmt.Formatter  = configkit.Secret{}
+	_ fmt.Stringer   = configkit.Path{}
+	_ json.Marshaler = configkit.Secret{}
+)
+
+func TestFacadeValuesRemainRootOwned(t *testing.T) {
+	t.Parallel()
+	const packagePath = "gitea.maximumdirect.net/eric/ConfigKit"
+	for _, candidate := range []reflect.Type{
+		reflect.TypeFor[configkit.Path](), reflect.TypeFor[configkit.Source](),
+		reflect.TypeFor[configkit.Secret](), reflect.TypeFor[configkit.Diagnostic](),
+		reflect.TypeFor[configkit.LoadError](), reflect.TypeFor[configkit.Metadata](),
+		reflect.TypeFor[configkit.Resolution](), reflect.TypeFor[configkit.Validation](),
+		reflect.TypeFor[configkit.Version](), reflect.TypeFor[configkit.VersionRule](),
+		reflect.TypeFor[configkit.FilesystemContext](), reflect.TypeFor[configkit.Override](),
+		reflect.TypeFor[configkit.Definition[struct{}]](), reflect.TypeFor[configkit.Options[struct{}]](),
+		reflect.TypeFor[configkit.Result[struct{}]](),
+		reflect.TypeFor[configkit.ValueSnapshot](), reflect.TypeFor[configkit.ValueChange](),
+		reflect.TypeFor[configkit.SecretReferenceInfo](), reflect.TypeFor[configkit.Explanation](),
+		reflect.TypeFor[configkit.SecretFileResult](), reflect.TypeFor[configkit.SecretsReport](),
+		reflect.TypeFor[configkit.SecretsError](),
+	} {
+		if candidate.PkgPath() != packagePath {
+			t.Fatalf("type %s belongs to %q", candidate, candidate.PkgPath())
+		}
+	}
+	secret := configkit.SecretEnv("SAFE_NAME")
+	formatted := fmt.Sprintf("%#v", secret)
+	encoded, err := json.Marshal(secret)
+	if formatted == "" || err != nil || string(encoded) != `"SAFE_NAME"` {
+		t.Fatalf("secret rendering = %q, %s, %v", formatted, encoded, err)
+	}
+	if got := configkit.Keys("a/b~").Index(0).String(); got != "/a~1b~0/0" {
+		t.Fatalf("path = %q", got)
+	}
+	if got := (&configkit.LoadError{}).Error(); got != "configkit: configuration load failed" {
+		t.Fatalf("zero LoadError = %q", got)
+	}
+}
+
+func TestFacadeInspectionUsesFrozenState(t *testing.T) {
+	t.Setenv("FACADE_INSPECTION_SECRET", "credential")
+
+	type configuration struct {
+		Value  string           `yaml:"value"`
+		Secret configkit.Secret `yaml:"secret"`
+	}
+	result, err := configkit.Load[configuration](configkit.Bytes("inspection.yml", []byte("value: original\nsecret: FACADE_INSPECTION_SECRET\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !result.Config.Secret.IsResolved() || result.Config.Secret.Value() != "credential" {
+		t.Fatalf("secret = %#v", result.Config.Secret)
+	}
+	explanation, ok := result.Explain(configkit.Keys("value"))
+	if !ok || explanation.Effective.YAML != "original\n" {
+		t.Fatalf("explanation = %#v, %v", explanation, ok)
+	}
+	explanation.Effective.YAML = "mutated\n"
+	result.Config.Value = "mutated"
+	var effective bytes.Buffer
+	if err := result.WriteEffective(&effective); err != nil || !strings.Contains(effective.String(), "value: original\n") || strings.Contains(effective.String(), "credential") {
+		t.Fatalf("effective = %q, %v", effective.String(), err)
+	}
+	again, ok := result.Explain(configkit.Keys("value"))
+	if !ok || again.Effective.YAML != "original\n" {
+		t.Fatalf("inspection changed = %#v, %v", again, ok)
+	}
+	secret, ok := result.Explain(configkit.Keys("secret"))
+	if !ok || secret.SecretReference == nil || secret.SecretReference.Name != "FACADE_INSPECTION_SECRET" {
+		t.Fatalf("secret explanation = %#v, %v", secret, ok)
+	}
+	var explanationOutput bytes.Buffer
+	if err := result.WriteExplanation(&explanationOutput, configkit.Keys("value")); err != nil || !strings.Contains(explanationOutput.String(), `path: "/value"`) {
+		t.Fatalf("explanation output = %q, %v", explanationOutput.String(), err)
+	}
+
+	unknown := bytes.NewBufferString("unchanged")
+	if err := result.WriteExplanation(unknown, configkit.Keys("unknown")); err == nil || unknown.String() != "unchanged" {
+		t.Fatalf("unknown explanation = %q, %v", unknown.String(), err)
+	}
+	var nilResult *configkit.Result[configuration]
+	if _, ok := nilResult.Explain(configkit.Keys("value")); ok {
+		t.Fatal("nil result explained a path")
+	}
+	if err := nilResult.WriteEffective(io.Discard); err == nil {
+		t.Fatal("nil result rendered effective configuration")
+	}
+}
+
+func TestFacadeSecretsBootstrapUsesFacadeRecords(t *testing.T) {
+	const (
+		loadedName   = "FACADE_BOOTSTRAP_LOADED"
+		existingName = "FACADE_BOOTSTRAP_EXISTING"
+	)
+	restore := func(name string) {
+		value, present := os.LookupEnv(name)
+		t.Cleanup(func() {
+			if present {
+				_ = os.Setenv(name, value)
+			} else {
+				_ = os.Unsetenv(name)
+			}
+		})
+	}
+	restore(loadedName)
+	restore(existingName)
+	if err := os.Unsetenv(loadedName); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Setenv(existingName, ""); err != nil {
+		t.Fatal(err)
+	}
+	directory := t.TempDir()
+	if err := os.WriteFile(directory+"/"+loadedName, []byte("bootstrap\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(directory+"/"+existingName, []byte("ignored\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	report, err := configkit.LoadSecretsDir(directory)
+	if err != nil {
+		t.Fatal(err)
+	}
+	entries := report.Entries()
+	if len(entries) != 2 || os.Getenv(loadedName) != "bootstrap" {
+		t.Fatalf("entries/environment = %#v / %q", entries, os.Getenv(loadedName))
+	}
+	status := map[string]configkit.SecretFileResult{}
+	for _, entry := range entries {
+		status[entry.Name] = entry
+	}
+	if status[loadedName].Status != configkit.SecretFileLoaded || status[existingName].Status != configkit.SecretFileSkippedExisting || !status[existingName].ExistingEmpty {
+		t.Fatalf("statuses = %#v", status)
+	}
+	entries[0].Name = "mutated"
+	if report.Entries()[0].Name == "mutated" {
+		t.Fatal("report entries share mutable state")
+	}
+	var rendered bytes.Buffer
+	if _, err := report.WriteTo(&rendered); err != nil || strings.Contains(rendered.String(), "bootstrap") || strings.Contains(rendered.String(), "ignored") {
+		t.Fatalf("report rendering = %q, %v", rendered.String(), err)
+	}
+
+	failedReport, err := configkit.LoadSecretsDir("")
+	var secretsError *configkit.SecretsError
+	if failedReport == nil || !errors.As(err, &secretsError) || len(secretsError.Diagnostics()) != 1 || secretsError.Diagnostics()[0].Code != configkit.CodeSecretsInvalidPath {
+		t.Fatalf("bootstrap failure = %#v / %#v", failedReport, err)
+	}
+}
+
+func TestFacadeLoadBridgesLifecycleCallbacks(t *testing.T) {
+	t.Setenv("FACADE_SECRET_NAME", "credential")
+
+	type configuration struct {
+		Version string            `yaml:"version"`
+		Input   int               `yaml:"input"`
+		Derived int               `yaml:"derived"`
+		Secret  configkit.Secret  `yaml:"secret"`
+		Labels  map[string]string `yaml:"labels"`
+	}
+	var retainedResolution *configkit.Resolution
+	var retainedValidation *configkit.Validation
+	versionCalls, defaultsCalls, resolveCalls, validateCalls := 0, 0, 0, 0
+	definition := configkit.Definition[configuration]{
+		Version: &configkit.VersionRule{Path: configkit.Keys("version"), Check: func(version configkit.Version, validation *configkit.Validation) error {
+			versionCalls++
+			retainedValidation = validation
+			if !version.Present || version.Text != "1" {
+				validation.Error(configkit.Keys("version"), "unsupported version")
+			}
+			return nil
+		}},
+		Defaults: func() configuration {
+			defaultsCalls++
+			return configuration{Derived: 1, Labels: map[string]string{"default": "kept"}}
+		},
+		Resolve: func(configuration *configuration, resolution *configkit.Resolution) error {
+			resolveCalls++
+			retainedResolution = resolution
+			if !resolution.IsExplicit(configkit.Keys("input")) {
+				resolution.Error(configkit.Keys("input"), "input is required")
+			}
+			input, ok := resolution.InputInfo(configkit.Keys("input"))
+			if !ok || !input.Explicit {
+				resolution.Error(configkit.Keys("input"), "missing input provenance")
+			}
+			source, ok := resolution.Source("source-1")
+			if !ok || source.Label != "facade.yml" {
+				resolution.Error(configkit.Keys("input"), "missing source")
+			}
+			configkit.Default(resolution, configkit.Keys("derived"), &configuration.Derived, configuration.Input*2, "derived from input", configkit.Keys("input"))
+			return nil
+		},
+		Validate: func(configuration *configuration, validation *configkit.Validation) {
+			validateCalls++
+			retainedValidation = validation
+			if !configuration.Secret.IsResolved() || configuration.Secret.Value() != "credential" {
+				validation.Error(configkit.Keys("secret"), "secret did not resolve")
+			}
+		},
+	}
+	if versionCalls != 0 || defaultsCalls != 0 || resolveCalls != 0 || validateCalls != 0 {
+		t.Fatal("callbacks ran while constructing options")
+	}
+
+	result, err := configkit.Load(configkit.Bytes("facade.yml", []byte("version: 1\ninput: 3\nsecret: FACADE_SECRET_NAME\n")), configkit.Options[configuration]{Definition: definition})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if versionCalls != 1 || defaultsCalls != 1 || resolveCalls != 1 || validateCalls != 1 || result.Config.Derived != 6 {
+		t.Fatalf("callback counts/configuration = %d/%d/%d/%d %#v", versionCalls, defaultsCalls, resolveCalls, validateCalls, result.Config)
+	}
+	derived, ok := result.Metadata().Lookup(configkit.Keys("derived"))
+	if !ok || derived.Explicit || derived.Origin.Operation != configkit.ChangeDerivedDefault {
+		t.Fatalf("derived metadata = %#v, %v", derived, ok)
+	}
+	if sources := result.Sources(); len(sources) != 1 || sources[0].Label != "facade.yml" {
+		t.Fatalf("sources = %#v", sources)
+	}
+	if result.Diagnostics() != nil {
+		t.Fatalf("diagnostics = %#v", result.Diagnostics())
+	}
+	for _, context := range []func(){
+		func() { retainedResolution.IsExplicit(configkit.Keys("input")) },
+		func() { retainedValidation.Warning(configkit.Keys("input"), "too late") },
+	} {
+		func() {
+			defer func() {
+				if recover() == nil {
+					t.Fatal("retained callback context remained active")
+				}
+			}()
+			context()
+		}()
+	}
+}
+
+func TestFacadeLoadReturnsFacadeLoadError(t *testing.T) {
+	t.Parallel()
+
+	type configuration struct {
+		Value int `yaml:"value"`
+	}
+	result, err := configkit.Load[configuration](configkit.Bytes("invalid.yml", []byte("value: wrong\n")))
+	if result != nil || err == nil {
+		t.Fatalf("result, err = %#v, %v", result, err)
+	}
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) || len(loadError.Diagnostics()) != 1 || loadError.Diagnostics()[0].Code != configkit.CodeDecodeType {
+		t.Fatalf("facade error = %#v", err)
+	}
+}

facade_compatibility_test.go

@@ -0,0 +1,85 @@
+package configkit_test
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"reflect"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+var (
+	_ error          = (*configkit.LoadError)(nil)
+	_ fmt.Formatter  = configkit.Secret{}
+	_ fmt.Stringer   = configkit.Path{}
+	_ json.Marshaler = configkit.Secret{}
+	_ io.WriterTo    = (*configkit.SecretsReport)(nil)
+)
+
+type facadeCompatibilityConfig struct {
+	Value   string `yaml:"value"`
+	Derived string `yaml:"derived"`
+}
+
+func TestFacadeCompatibility(t *testing.T) {
+	t.Parallel()
+
+	const packagePath = "gitea.maximumdirect.net/eric/ConfigKit"
+	for _, candidate := range []struct {
+		name  string
+		type_ reflect.Type
+	}{
+		{"Path", reflect.TypeFor[configkit.Path]()},
+		{"Source", reflect.TypeFor[configkit.Source]()},
+		{"Secret", reflect.TypeFor[configkit.Secret]()},
+		{"Definition", reflect.TypeFor[configkit.Definition[facadeCompatibilityConfig]]()},
+		{"Options", reflect.TypeFor[configkit.Options[facadeCompatibilityConfig]]()},
+		{"Result", reflect.TypeFor[configkit.Result[facadeCompatibilityConfig]]()},
+	} {
+		if candidate.type_.PkgPath() != packagePath {
+			t.Errorf("%s belongs to %q, want %q", candidate.name, candidate.type_.PkgPath(), packagePath)
+		}
+	}
+
+	constructed := configkit.Options[facadeCompatibilityConfig]{
+		Definition: configkit.Definition[facadeCompatibilityConfig]{},
+		Filesystem: &configkit.FilesystemContext{BaseDir: "configs", Root: "configs"},
+		Overrides: []configkit.Override{{
+			Path:  configkit.Keys("value"),
+			Value: "override",
+			Flag:  "--value",
+		}},
+	}
+	if got := constructed.Overrides[0].Path.String(); got != "/value" {
+		t.Fatalf("constructed override path = %q, want /value", got)
+	}
+	publicResult := configkit.Result[facadeCompatibilityConfig]{Config: facadeCompatibilityConfig{Value: "constructed"}}
+	if publicResult.Config.Value != "constructed" {
+		t.Fatal("constructed result lost its public configuration")
+	}
+
+	result, err := configkit.Load(configkit.Bytes("facade.yml", []byte("value: input\n")), configkit.Options[facadeCompatibilityConfig]{
+		Definition: configkit.Definition[facadeCompatibilityConfig]{
+			Resolve: func(configuration *facadeCompatibilityConfig, resolution *configkit.Resolution) error {
+				configkit.Default(resolution, configkit.Keys("derived"), &configuration.Derived, configuration.Value+" default", "derive value")
+				configkit.Normalize(resolution, configkit.Keys("value"), &configuration.Value, "normalized "+configuration.Value, "normalize value")
+				return nil
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if result.Config != (facadeCompatibilityConfig{Value: "normalized input", Derived: "input default"}) {
+		t.Fatalf("Load() Config = %#v", result.Config)
+	}
+
+	_, err = configkit.Load[facadeCompatibilityConfig](configkit.Bytes("invalid.yml", []byte("value: [\n")))
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) {
+		t.Fatalf("Load() error = %T, want *configkit.LoadError", err)
+	}
+}

facade_context_test.go

@@ -0,0 +1,51 @@
+package configkit_test
+
+import (
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+func TestFacadeInactiveContextsPreserveClosedFailure(t *testing.T) {
+	t.Parallel()
+	for _, state := range []struct {
+		name       string
+		resolution *configkit.Resolution
+		validation *configkit.Validation
+	}{
+		{name: "nil"},
+		{name: "zero", resolution: &configkit.Resolution{}, validation: &configkit.Validation{}},
+	} {
+		t.Run(state.name, func(t *testing.T) {
+			path := configkit.Keys("value")
+			var target int
+			for _, operation := range []struct {
+				name string
+				call func()
+			}{
+				{"IsExplicit", func() { state.resolution.IsExplicit(path) }},
+				{"InputInfo", func() { state.resolution.InputInfo(path) }},
+				{"Source", func() { state.resolution.Source("source") }},
+				{"Record", func() { state.resolution.Record(path, configkit.ChangeNormalization, "reason") }},
+				{"Resolution.Error", func() { state.resolution.Error(path, "message") }},
+				{"Resolution.Warning", func() { state.resolution.Warning(path, "message") }},
+				{"Default", func() { configkit.Default(state.resolution, path, &target, 1, "reason") }},
+				{"Normalize", func() { configkit.Normalize(state.resolution, path, &target, 1, "reason") }},
+				{"Validation.Error", func() { state.validation.Error(path, "message") }},
+				{"Validation.Warning", func() { state.validation.Warning(path, "message") }},
+			} {
+				t.Run(operation.name, func(t *testing.T) {
+					defer func() {
+						if got := recover(); got != "configkit: callback context is no longer active" {
+							t.Errorf("panic = %v; want fixed closed-context failure", got)
+						}
+						if target != 0 {
+							t.Error("inactive helper changed target")
+						}
+					}()
+					operation.call()
+				})
+			}
+		})
+	}
+}

facade_internal_test.go

@@ -0,0 +1,52 @@
+package configkit
+
+import (
+	"errors"
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/engine"
+)
+
+func TestWrappedSourcesPreserveEngineOwnership(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Value string `yaml:"value"`
+	}
+	data := []byte("value: retained\n")
+	source := Bytes("snapshot.yml", data)
+	data[7] = 'X'
+	result, err := engine.Load[config](source.toEngine(), engine.SecretBinding{})
+	if err != nil || result.Config.Value != "retained" {
+		t.Fatalf("snapshotted source = %#v, %v", result, err)
+	}
+
+	readerSource := Reader("reader.yml", strings.NewReader("value: once\n"))
+	first := readerSource
+	if _, err := engine.Load[config](first.toEngine(), engine.SecretBinding{}); err != nil {
+		t.Fatal(err)
+	}
+	_, err = engine.Load[config](readerSource.toEngine(), engine.SecretBinding{})
+	var loadError *engine.LoadError
+	if !errors.As(err, &loadError) || len(loadError.Diagnostics()) != 1 || loadError.Diagnostics()[0].Code != engine.CodeSourceReaderUsed {
+		t.Fatalf("copied reader source error = %#v", err)
+	}
+}
+
+func TestWrappedPathsRetainEngineSegmentIntent(t *testing.T) {
+	t.Parallel()
+
+	parsed, err := ParsePath("/0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	keyed, indexed := Keys("0"), Path{}.Index(0)
+	if parsed.String() != "/0" || keyed.String() != "/0" || indexed.String() != "/0" {
+		t.Fatalf("path spellings = %q, %q, %q", parsed, keyed, indexed)
+	}
+	if reflect.DeepEqual(parsed.value, keyed.value) || reflect.DeepEqual(parsed.value, indexed.value) || reflect.DeepEqual(keyed.value, indexed.value) {
+		t.Fatal("path wrappers collapsed parsed, mapping-key, and index segments")
+	}
+}

facade_version_test.go

@@ -0,0 +1,66 @@
+package configkit_test
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+type versionCountingReader struct {
+	*strings.Reader
+	reads int
+}
+
+func (r *versionCountingReader) Read(data []byte) (int, error) {
+	r.reads++
+	return r.Reader.Read(data)
+}
+
+func TestFacadeRejectsMissingVersionCheckerBeforeReading(t *testing.T) {
+	t.Parallel()
+	type configuration struct {
+		Version string `yaml:"version"`
+	}
+	reader := &versionCountingReader{Reader: strings.NewReader("version: v1\n")}
+	source := configkit.Reader("version.yml", reader)
+	var defaults, resolutions, validations, checks int
+	options := configkit.Options[configuration]{Definition: configkit.Definition[configuration]{
+		Version:  &configkit.VersionRule{Path: configkit.Keys("version")},
+		Defaults: func() configuration { defaults++; return configuration{} },
+		Resolve:  func(*configuration, *configkit.Resolution) error { resolutions++; return nil },
+		Validate: func(*configuration, *configkit.Validation) { validations++ },
+	}}
+	result, err := configkit.Load(source, options)
+	var loadError *configkit.LoadError
+	if result != nil || !errors.As(err, &loadError) {
+		t.Fatalf("missing checker: result = %v, error = %v", result, err)
+	}
+	diagnostics := loadError.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeOptionsInvalid {
+		t.Fatalf("diagnostics = %v", diagnostics)
+	}
+	if reader.reads != 0 || defaults != 0 || resolutions != 0 || validations != 0 {
+		t.Fatalf("invalid options performed work: reads=%d defaults=%d resolve=%d validate=%d", reader.reads, defaults, resolutions, validations)
+	}
+	options.Definition.Version.Check = func(version configkit.Version, validation *configkit.Validation) error {
+		checks++
+		if version != (configkit.Version{Present: true, Text: "v1"}) {
+			t.Errorf("version = %#v", version)
+		}
+		validation.Warning(configkit.Keys("version"), "version accepted")
+		return nil
+	}
+	result, err = configkit.Load(source, options)
+	if err != nil || result == nil || result.Config.Version != "v1" {
+		t.Fatalf("reuse with checker: result = %v, error = %v", result, err)
+	}
+	if checks != 1 || defaults != 1 || resolutions != 1 || validations != 1 {
+		t.Fatalf("callback counts: check=%d defaults=%d resolve=%d validate=%d", checks, defaults, resolutions, validations)
+	}
+	diagnostics = result.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeVersionWarning {
+		t.Fatalf("version callback diagnostics = %v", diagnostics)
+	}
+}

go.mod

@@ -0,0 +1,5 @@
+module gitea.maximumdirect.net/eric/ConfigKit
+
+go 1.25.0
+
+require go.yaml.in/yaml/v4 v4.0.0-rc.6

go.sum

@@ -0,0 +1,2 @@
+go.yaml.in/yaml/v4 v4.0.0-rc.6 h1:1h7H1ohdUh93/FyE4YaDa1Zh64K6VVbjF4K6WUxMtH4=
+go.yaml.in/yaml/v4 v4.0.0-rc.6/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=

import_boundary_test.go

@@ -0,0 +1,59 @@
+package configkit
+
+import (
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestDependencyImportBoundary(t *testing.T) {
+	t.Parallel()
+
+	err := filepath.WalkDir(".", func(path string, entry fs.DirEntry, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+		if entry.IsDir() {
+			if path == ".git" {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if filepath.Ext(path) != ".go" {
+			return nil
+		}
+		file, err := parser.ParseFile(token.NewFileSet(), path, nil, parser.ImportsOnly)
+		if err != nil {
+			return err
+		}
+		for _, imported := range file.Imports {
+			importPath, err := strconv.Unquote(imported.Path.Value)
+			if err != nil {
+				return err
+			}
+			if strings.HasPrefix(importPath, "go.yaml.in/yaml/") && !strings.HasPrefix(filepath.ToSlash(path), "internal/yaml/") {
+				t.Errorf("%s imports private YAML dependency %s", path, importPath)
+			}
+			if strings.HasPrefix(importPath, "github.com/google/go-cmp/") && !strings.HasSuffix(path, "_test.go") {
+				t.Errorf("%s imports test-only dependency %s", path, importPath)
+			}
+			production := !strings.HasSuffix(path, "_test.go")
+			rootProduction := production && filepath.Dir(path) == "."
+			internalProduction := production && strings.HasPrefix(filepath.ToSlash(path), "internal/")
+			if rootProduction && strings.HasPrefix(importPath, "gitea.maximumdirect.net/eric/ConfigKit/internal/") && importPath != "gitea.maximumdirect.net/eric/ConfigKit/internal/engine" {
+				t.Errorf("%s bypasses the engine boundary through %s", path, importPath)
+			}
+			if internalProduction && importPath == "gitea.maximumdirect.net/eric/ConfigKit" {
+				t.Errorf("%s imports the public root package", path)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+}

inspection.go

@@ -0,0 +1,70 @@
+package configkit
+
+import (
+	"io"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/engine"
+)
+
+// ValueSnapshot is a detached, deterministic YAML representation of one value.
+// Present distinguishes absence or deletion from an explicit null value.
+type ValueSnapshot struct {
+	Present  bool
+	Redacted bool
+	YAML     string
+}
+
+// ValueChange describes one explicit definition or audited domain operation.
+type ValueChange struct {
+	Before       ValueSnapshot
+	After        ValueSnapshot
+	Origin       Origin
+	Reasons      []string
+	Dependencies []Path
+}
+
+// SecretReferenceInfo describes a successfully resolved effective reference.
+// Name is the environment-variable name, never its value.
+type SecretReferenceInfo struct {
+	Name string
+}
+
+// Explanation is a detached safe account of one effective or historical path.
+type Explanation struct {
+	Path            Path
+	Effective       ValueSnapshot
+	Origin          Origin
+	History         []ValueChange
+	SecretReference *SecretReferenceInfo
+}
+
+// Explain returns safe effective and chronological values for a known final or
+// historical path. Unknown and malformed paths return false.
+func (r *Result[T]) Explain(path Path) (Explanation, bool) {
+	if r == nil {
+		return Explanation{}, false
+	}
+	value, ok := r.inspection.Explain(toEnginePath(path))
+	return fromEngineExplanation(value), ok
+}
+
+// WriteEffective writes deterministic redacted YAML from the frozen resolved
+// snapshot. The output is intended for inspection and is not promised reloadable.
+// Writer errors, including short writes, are returned and may leave partial output.
+func (r *Result[T]) WriteEffective(output io.Writer) error {
+	if r == nil {
+		var inspection *engine.Inspection
+		return inspection.WriteEffective(output)
+	}
+	return r.inspection.WriteEffective(output)
+}
+
+// WriteExplanation writes a deterministic human-readable rendering of Explain.
+// Unknown paths produce no output. Writer failures may leave partial output.
+func (r *Result[T]) WriteExplanation(output io.Writer, path Path) error {
+	if r == nil {
+		var inspection *engine.Inspection
+		return inspection.WriteExplanation(output, toEnginePath(path))
+	}
+	return r.inspection.WriteExplanation(output, toEnginePath(path))
+}

internal/document/document.go

@@ -0,0 +1,65 @@
+// Package document defines ConfigKit's parser-independent configuration tree.
+package document
+
+// Kind identifies a configuration node category.
+type Kind uint8
+
+const (
+	Mapping Kind = iota + 1
+	Sequence
+	String
+	Boolean
+	Number
+	Null
+)
+
+// Location identifies a source coordinate. Root depth and unavailable coordinates
+// are represented independently by callers; line and column are one-based when set.
+type Location struct {
+	SourceID string
+	Line     int
+	Column   int
+}
+
+// Entry is an ordered mapping entry with separate key and value locations.
+type Entry struct {
+	Key           string
+	KeyLocation   Location
+	ValueLocation Location
+	Value         *Node
+}
+
+// Node is ConfigKit's owned configuration representation. Number Text retains its
+// exact validated decimal spelling; Boolean Text is "true" or "false".
+type Node struct {
+	// Sensitive preserves field classification from concrete typed projections.
+	// It is metadata, not part of the configuration value or emitted YAML.
+	Sensitive bool
+	Kind      Kind
+	Location  Location
+	Text      string
+	Mapping   []Entry
+	Sequence  []*Node
+}
+
+// Clone returns a detached copy of a node tree.
+func Clone(node *Node) *Node {
+	if node == nil {
+		return nil
+	}
+	cloned := *node
+	if node.Mapping != nil {
+		cloned.Mapping = make([]Entry, len(node.Mapping))
+		for i, entry := range node.Mapping {
+			cloned.Mapping[i] = entry
+			cloned.Mapping[i].Value = Clone(entry.Value)
+		}
+	}
+	if node.Sequence != nil {
+		cloned.Sequence = make([]*Node, len(node.Sequence))
+		for i, child := range node.Sequence {
+			cloned.Sequence[i] = Clone(child)
+		}
+	}
+	return &cloned
+}

internal/engine/callback_ownership_test.go

@@ -0,0 +1,52 @@
+package engine
+
+import "testing"
+
+func TestCallbackAssignmentsAreDetachedAcrossLoads(t *testing.T) {
+	type object struct{ Value string }
+	type cfg struct {
+		Map     map[string][]*object
+		Pointer *object
+		Secret  Secret
+	}
+	for _, validatorAssignment := range []bool{false, true} {
+		name := "resolver"
+		if validatorAssignment {
+			name = "validator"
+		}
+		t.Run(name, func(t *testing.T) {
+			external := &object{Value: "original"}
+			shared := map[string][]*object{"key": {external}}
+			definition := Definition[cfg]{Resolve: func(c *cfg, r *Resolution) error {
+				Normalize(r, Keys("map"), &c.Map, shared, "populate")
+				c.Pointer = external
+				r.Record(Keys("pointer"), ChangeNormalization, "populate")
+				c.Secret = SecretEnv("CONFIGKIT_CALLBACK_SECRET")
+				r.Record(Keys("secret"), ChangeNormalization, "reference")
+				return nil
+			}}
+			if validatorAssignment {
+				definition.Validate = func(c *cfg, v *Validation) { c.Map = shared; c.Pointer = external }
+			}
+			calls := 0
+			lookup := func(string) (string, bool) { calls++; return "credential", true }
+			first, err := testLoadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
+			if err != nil {
+				t.Fatal(err)
+			}
+			second, err := testLoadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
+			if err != nil {
+				t.Fatal(err)
+			}
+			first.Config.Map["key"][0].Value = "changed"
+			first.Config.Pointer.Value = "changed pointer"
+			external.Value = "external change"
+			if second.Config.Map["key"][0].Value != "original" || second.Config.Pointer.Value != "original" {
+				t.Fatal("published configuration shares callback state")
+			}
+			if second.Config.Secret.Value() != "credential" || !second.Config.Secret.IsResolved() || calls != 2 {
+				t.Fatal("publication changed secret state or repeated environment lookup")
+			}
+		})
+	}
+}

internal/engine/clone.go

@@ -0,0 +1,159 @@
+package engine
+
+import (
+	"encoding"
+	"math"
+	"reflect"
+)
+
+// secretCloneMode distinguishes fresh unresolved references from publication of
+// already validated private state, which must not trigger another lookup.
+type secretCloneMode uint8
+
+const (
+	cloneUnresolvedSecrets secretCloneMode = iota
+	cloneValidatedSecrets
+)
+
+func cloneConfiguration(schema *schemaDescriptor, value reflect.Value, limits projectionLimits) (reflect.Value, *projectionIssue) {
+	return cloneConfigurationWithMode(schema, value, limits, cloneUnresolvedSecrets)
+}
+
+func cloneConfigurationWithMode(schema *schemaDescriptor, value reflect.Value, limits projectionLimits, mode secretCloneMode) (reflect.Value, *projectionIssue) {
+	if schema == nil || schema.root == nil || !value.IsValid() || value.Type() != schema.root.typeOf {
+		return reflect.Value{}, &projectionIssue{code: CodeSchemaUnsupportedType, message: "configuration value does not match its schema"}
+	}
+	operation := valueOperation{schema: schema, limits: limits, active: make(map[valueVisit]bool), cloneMode: mode}
+	return operation.clone(value, schema.root, Path{}, 0)
+}
+
+func (o *valueOperation) clone(value reflect.Value, descriptor *typeDescriptor, path Path, depth int) (reflect.Value, *projectionIssue) {
+	if issue := o.checkDepth(path, depth); issue != nil {
+		return reflect.Value{}, issue
+	}
+	if descriptor.kind == descriptorPointer {
+		if value.IsNil() {
+			return reflect.Zero(value.Type()), nil
+		}
+		leave, issue := o.enter(value, path)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		defer leave()
+		child, issue := o.clone(value.Elem(), descriptor.element, path, depth)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		result := reflect.New(value.Type().Elem())
+		result.Elem().Set(child)
+		return result, nil
+	}
+
+	switch descriptor.kind {
+	case descriptorStruct:
+		result := reflect.New(value.Type()).Elem()
+		for _, member := range descriptor.members {
+			memberPath, memberDepth := path, depth
+			if !member.inline {
+				memberPath, memberDepth = path.Key(member.name), depth+1
+			}
+			cloned, issue := o.clone(value.Field(member.index), member.descriptor, memberPath, memberDepth)
+			if issue != nil {
+				return reflect.Value{}, issue
+			}
+			result.Field(member.index).Set(cloned)
+		}
+		return result, nil
+	case descriptorMap:
+		if value.IsNil() {
+			return reflect.Zero(value.Type()), nil
+		}
+		leave, issue := o.enter(value, path)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		defer leave()
+		result := reflect.MakeMapWithSize(value.Type(), value.Len())
+		for _, key := range value.MapKeys() {
+			cloned, issue := o.clone(value.MapIndex(key), descriptor.element, path.Key(key.String()), depth+1)
+			if issue != nil {
+				return reflect.Value{}, issue
+			}
+			result.SetMapIndex(key, cloned)
+		}
+		return result, nil
+	case descriptorSlice:
+		if value.IsNil() {
+			return reflect.Zero(value.Type()), nil
+		}
+		leave, issue := o.enter(value, path)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		defer leave()
+		result := reflect.MakeSlice(value.Type(), value.Len(), value.Len())
+		for i := 0; i < value.Len(); i++ {
+			cloned, issue := o.clone(value.Index(i), descriptor.element, path.Index(i), depth+1)
+			if issue != nil {
+				return reflect.Value{}, issue
+			}
+			result.Index(i).Set(cloned)
+		}
+		return result, nil
+	case descriptorArray:
+		result := reflect.New(value.Type()).Elem()
+		for i := 0; i < value.Len(); i++ {
+			cloned, issue := o.clone(value.Index(i), descriptor.element, path.Index(i), depth+1)
+			if issue != nil {
+				return reflect.Value{}, issue
+			}
+			result.Index(i).Set(cloned)
+		}
+		return result, nil
+	case descriptorDynamic:
+		if value.IsNil() {
+			return reflect.Zero(value.Type()), nil
+		}
+		concrete := value.Elem()
+		dynamic, issue := o.dynamicDescriptor(concrete.Type(), path)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		cloned, issue := o.clone(concrete, dynamic, path, depth)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		result := reflect.New(value.Type()).Elem()
+		result.Set(cloned)
+		return result, nil
+	case descriptorSecret:
+		result := reflect.New(value.Type()).Elem()
+		reference := o.schema.secrets.Read(value)
+		if o.cloneMode == cloneValidatedSecrets {
+			result.Set(value)
+		} else if reference.Specified {
+			result.Set(o.schema.secrets.Make(SecretState{Name: reference.Name, Specified: true}))
+		}
+		return result, nil
+	case descriptorText:
+		text, issue := marshalCanonicalText(value, path)
+		if issue != nil {
+			return reflect.Value{}, issue
+		}
+		result := reflect.New(value.Type()).Elem()
+		unmarshaler := result.Addr().Interface().(encoding.TextUnmarshaler)
+		if err := unmarshaler.UnmarshalText([]byte(text)); err != nil {
+			return reflect.Value{}, &projectionIssue{code: CodeSchemaCodec, path: path.clone(), message: "custom text scalar could not be reconstructed"}
+		}
+		return result, nil
+	case descriptorFloat:
+		if math.IsNaN(value.Float()) || math.IsInf(value.Float(), 0) {
+			return reflect.Value{}, &projectionIssue{code: CodeSchemaNonFinite, path: path.clone(), message: "configuration float must be finite"}
+		}
+		fallthrough
+	default:
+		result := reflect.New(value.Type()).Elem()
+		result.Set(value)
+		return result, nil
+	}
+}

internal/engine/compose.go

@@ -0,0 +1,190 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+// composedDocument is the private handoff between source assembly and later
+// precedence layers. Claims remain ordered by source and declaration traversal;
+// origins retain every source that contributes to a composite mapping.
+type composedDocument struct {
+	root         *document.Node
+	claims       []compositionClaim
+	origins      map[string]Origin
+	overlays     []overlayRecord
+	applications []historyApplication
+	inputBytes   int64
+	inputNodes   int
+}
+
+// cloneComposedDocument detaches mutable composition and provenance state;
+// history application trees are immutable and retain their existing sharing.
+func cloneComposedDocument(base *composedDocument) *composedDocument {
+	return &composedDocument{
+		root: document.Clone(base.root), claims: cloneCompositionClaims(base.claims),
+		origins: cloneOriginIndex(base.origins), overlays: cloneOverlayRecords(base.overlays),
+		applications: cloneHistoryApplications(base.applications),
+		inputBytes:   base.inputBytes, inputNodes: base.inputNodes,
+	}
+}
+
+type compositionClaim struct {
+	path     Path
+	kind     document.Kind
+	location Location
+}
+
+type compositionClaims struct {
+	ordered []compositionClaim
+	byPath  map[string][]compositionClaim
+}
+
+// composeDocuments recursively joins disjoint mapping entries. Source order
+// controls only output traversal and diagnostics: every non-mapping overlap is
+// rejected before a result is assembled.
+func composeDocuments(inputs ...*document.Node) (*composedDocument, []Diagnostic) {
+	if len(inputs) == 0 {
+		return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires at least one document", nil)}
+	}
+
+	collected := compositionClaims{byPath: make(map[string][]compositionClaim)}
+	for _, input := range inputs {
+		if input == nil || input.Kind != document.Mapping {
+			var location *Location
+			if input != nil {
+				converted := publicLocation(input.Location)
+				location = &converted
+			}
+			return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires mapping document roots", location)}
+		}
+		collected.append(input, Path{})
+	}
+
+	for _, claim := range collected.ordered {
+		claims := collected.byPath[claim.path.String()]
+		if len(claims) < 2 || allMappingClaims(claims) {
+			continue
+		}
+		return nil, []Diagnostic{compositionConflictDiagnostic(claim.path, claims)}
+	}
+
+	root := document.Clone(inputs[0])
+	for _, input := range inputs[1:] {
+		mergeDisjointMappings(root, input)
+	}
+	applications := make([]historyApplication, 0, len(inputs))
+	for _, input := range inputs {
+		applications = append(applications, historyApplication{layer: LayerBase, value: input})
+	}
+	return &composedDocument{
+		root:         root,
+		claims:       cloneCompositionClaims(collected.ordered),
+		origins:      compositionOrigins(collected.ordered),
+		applications: applications,
+	}, nil
+}
+
+func (c *compositionClaims) append(node *document.Node, path Path) {
+	claim := compositionClaim{
+		path:     path.clone(),
+		kind:     node.Kind,
+		location: publicLocation(node.Location),
+	}
+	c.ordered = append(c.ordered, claim)
+	pointer := path.String()
+	c.byPath[pointer] = append(c.byPath[pointer], claim)
+
+	if node.Kind != document.Mapping {
+		return
+	}
+	for _, entry := range node.Mapping {
+		c.append(entry.Value, path.Key(entry.Key))
+	}
+}
+
+func allMappingClaims(claims []compositionClaim) bool {
+	for _, claim := range claims {
+		if claim.kind != document.Mapping {
+			return false
+		}
+	}
+	return true
+}
+
+func mergeDisjointMappings(target, incoming *document.Node) {
+	for _, incomingEntry := range incoming.Mapping {
+		index := documentEntryIndex(target.Mapping, incomingEntry.Key)
+		if index < 0 {
+			cloned := incomingEntry
+			cloned.Value = document.Clone(incomingEntry.Value)
+			target.Mapping = append(target.Mapping, cloned)
+			continue
+		}
+		// Claim validation guarantees that the only remaining overlap is a
+		// mapping pair. Empty mappings naturally contribute no child entries.
+		mergeDisjointMappings(target.Mapping[index].Value, incomingEntry.Value)
+	}
+}
+
+func documentEntryIndex(entries []document.Entry, key string) int {
+	for index := range entries {
+		if entries[index].Key == key {
+			return index
+		}
+	}
+	return -1
+}
+
+func compositionOrigins(claims []compositionClaim) map[string]Origin {
+	origins := make(map[string]Origin, len(claims))
+	for _, claim := range claims {
+		pointer := claim.path.String()
+		origin := origins[pointer]
+		origin.Layer = LayerBase
+		origin.Locations = append(origin.Locations, claim.location)
+		origins[pointer] = origin
+	}
+	return origins
+}
+
+func applyCompositionOrigins(decoded *decodedConfiguration, origins map[string]Origin) {
+	for pointer, origin := range origins {
+		if _, present := decoded.presence[pointer]; present {
+			decoded.origins[pointer] = cloneOrigin(origin)
+		}
+	}
+}
+
+func cloneCompositionClaims(claims []compositionClaim) []compositionClaim {
+	cloned := make([]compositionClaim, len(claims))
+	for index, claim := range claims {
+		cloned[index] = claim
+		cloned[index].path = claim.path.clone()
+	}
+	return cloned
+}
+
+func compositionInvalidDiagnostic(message string, location *Location) Diagnostic {
+	return Diagnostic{
+		Code: CodeComposeInvalid, Severity: SeverityError, Message: message,
+		Primary: cloneLocation(location),
+	}
+}
+
+func compositionConflictDiagnostic(path Path, claims []compositionClaim) Diagnostic {
+	primary := claims[0].location
+	related := make([]Location, 0, len(claims)-1)
+	for _, claim := range claims[1:] {
+		related = append(related, claim.location)
+	}
+	return Diagnostic{
+		Code:     CodeComposeConflict,
+		Severity: SeverityError,
+		Path:     path.clone(),
+		Message:  "configuration path is defined by multiple sources",
+		Primary:  &primary,
+		Related:  related,
+	}
+}
+
+func publicLocation(location document.Location) Location {
+	return Location{SourceID: location.SourceID, Line: location.Line, Column: location.Column}
+}

internal/engine/compose_test.go

@@ -0,0 +1,194 @@
+package engine
+
+import (
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestComposeDocumentsJoinsDisjointMappingsAndTracksClaims(t *testing.T) {
+	base := parseCompositionDocument(t, "source-1", `services:
+  api:
+    enabled: true
+empty: {}
+`)
+	fragment := parseCompositionDocument(t, "source-2", `services:
+  worker:
+    enabled: false
+values: [one, two]
+`)
+	baseBefore := document.Clone(base)
+	fragmentBefore := document.Clone(fragment)
+
+	composed, diagnostics := composeDocuments(base, fragment)
+	if len(diagnostics) != 0 {
+		t.Fatalf("composeDocuments() diagnostics = %#v", diagnostics)
+	}
+	for _, path := range []Path{
+		Keys("services", "api", "enabled"),
+		Keys("services", "worker", "enabled"),
+		Keys("empty"),
+		Keys("values"),
+	} {
+		if _, ok := documentAtPath(composed.root, path); !ok {
+			t.Errorf("composed document is missing %s", path.String())
+		}
+	}
+
+	serviceOrigin := composed.origins[Keys("services").String()]
+	wantLocations := []Location{
+		{SourceID: "source-1", Line: 2, Column: 3},
+		{SourceID: "source-2", Line: 2, Column: 3},
+	}
+	if !reflect.DeepEqual(serviceOrigin, Origin{Layer: LayerBase, Locations: wantLocations}) {
+		t.Fatalf("services origin = %#v, want composite origin", serviceOrigin)
+	}
+	wantClaimPaths := []string{"", "/services", "/services/api", "/services/api/enabled", "/empty", "", "/services", "/services/worker", "/services/worker/enabled", "/values"}
+	gotClaimPaths := make([]string, len(composed.claims))
+	for index, claim := range composed.claims {
+		gotClaimPaths[index] = claim.path.String()
+	}
+	if !reflect.DeepEqual(gotClaimPaths, wantClaimPaths) {
+		t.Fatalf("claim paths = %#v, want %#v", gotClaimPaths, wantClaimPaths)
+	}
+	reversed, reversedDiagnostics := composeDocuments(fragment, base)
+	if len(reversedDiagnostics) != 0 {
+		t.Fatalf("reversed composeDocuments() diagnostics = %#v", reversedDiagnostics)
+	}
+	if deltas := compareConfigurationValues(composed.root, reversed.root); len(deltas) != 0 {
+		t.Fatalf("input order changed effective values: %#v", deltas)
+	}
+
+	if !reflect.DeepEqual(base, baseBefore) || !reflect.DeepEqual(fragment, fragmentBefore) {
+		t.Fatal("composition mutated an input document")
+	}
+	composed.root.Mapping[0].Value.Mapping[0].Value.Mapping[0].Value.Text = "changed"
+	if !reflect.DeepEqual(base, baseBefore) || !reflect.DeepEqual(fragment, fragmentBefore) {
+		t.Fatal("composed document aliases an input document")
+	}
+}
+
+func TestComposeDocumentsRejectsEveryPresentNonMappingOverlap(t *testing.T) {
+	tests := []struct {
+		name  string
+		left  string
+		right string
+		path  string
+	}{
+		{name: "equal scalar", left: "value: true\n", right: "value: true\n", path: "/value"},
+		{name: "different scalar", left: "value: true\n", right: "value: false\n", path: "/value"},
+		{name: "null", left: "value: null\n", right: "value: null\n", path: "/value"},
+		{name: "sequence", left: "value: [one]\n", right: "value: [two]\n", path: "/value"},
+		{name: "mapping and scalar", left: "value:\n  nested: true\n", right: "value: text\n", path: "/value"},
+		{name: "scalar and mapping", left: "value: text\n", right: "value:\n  nested: true\n", path: "/value"},
+		{name: "nested keyed entry", left: "items:\n  shared:\n    left: 1\n", right: "items:\n  shared:\n    left: 2\n", path: "/items/shared/left"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			left := parseCompositionDocument(t, "source-1", test.left)
+			right := parseCompositionDocument(t, "source-2", test.right)
+			_, diagnostics := composeDocuments(left, right)
+			assertCompositionConflict(t, diagnostics, test.path, []string{"source-1", "source-2"})
+		})
+	}
+}
+
+func TestComposeDocumentsReportsAllClaimantsAtExactLocations(t *testing.T) {
+	first := parseCompositionDocument(t, "source-1", "group:\n  value: 1\n")
+	second := parseCompositionDocument(t, "source-2", "group:\n  value: 2\n")
+	third := parseCompositionDocument(t, "source-3", "group:\n  value: 3\n")
+
+	_, diagnostics := composeDocuments(first, second, third)
+	assertCompositionConflict(t, diagnostics, "/group/value", []string{"source-1", "source-2", "source-3"})
+	locations := append([]Location{*diagnostics[0].Primary}, diagnostics[0].Related...)
+	for _, location := range locations {
+		if location.Line != 2 || location.Column != 10 {
+			t.Fatalf("claim location = %#v, want line 2 column 10", location)
+		}
+	}
+
+	_, diagnostics = composeDocuments(
+		parseCompositionDocument(t, "source-1", "group:\n  left: 1\n"),
+		parseCompositionDocument(t, "source-2", "group:\n  right: 2\n"),
+		parseCompositionDocument(t, "source-3", "group: blocked\n"),
+	)
+	assertCompositionConflict(t, diagnostics, "/group", []string{"source-1", "source-2", "source-3"})
+}
+
+func TestComposeDocumentsTreatsEmptyMappingsAsChildlessContributions(t *testing.T) {
+	empty, diagnostics := composeDocuments(
+		parseCompositionDocument(t, "source-1", "{}\n"),
+		parseCompositionDocument(t, "source-2", "{}\n"),
+	)
+	if len(diagnostics) != 0 || len(empty.root.Mapping) != 0 || len(empty.origins[""].Locations) != 2 {
+		t.Fatalf("empty root composition = (%#v, %#v)", empty, diagnostics)
+	}
+
+	tests := []struct {
+		name  string
+		left  string
+		right string
+	}{
+		{name: "two empty mappings", left: "value: {}\n", right: "value: {}\n"},
+		{name: "empty then populated", left: "value: {}\n", right: "value: {nested: true}\n"},
+		{name: "populated then empty", left: "value: {nested: true}\n", right: "value: {}\n"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			composed, diagnostics := composeDocuments(
+				parseCompositionDocument(t, "source-1", test.left),
+				parseCompositionDocument(t, "source-2", test.right),
+			)
+			if len(diagnostics) != 0 {
+				t.Fatalf("composeDocuments() diagnostics = %#v", diagnostics)
+			}
+			if origin := composed.origins["/value"]; len(origin.Locations) != 2 {
+				t.Fatalf("value origin = %#v, want both mapping locations", origin)
+			}
+			if test.name != "two empty mappings" {
+				if _, ok := documentAtPath(composed.root, Keys("value", "nested")); !ok {
+					t.Fatal("populated mapping contribution was not retained")
+				}
+			}
+		})
+	}
+}
+
+func TestComposeDocumentsRejectsInvalidBoundaries(t *testing.T) {
+	if composed, diagnostics := composeDocuments(); composed != nil || len(diagnostics) != 1 || diagnostics[0].Code != CodeComposeInvalid {
+		t.Fatalf("empty composition = (%#v, %#v)", composed, diagnostics)
+	}
+	nonMapping := &document.Node{Kind: document.String, Location: document.Location{SourceID: "source-1", Line: 4, Column: 2}}
+	if composed, diagnostics := composeDocuments(nonMapping); composed != nil || len(diagnostics) != 1 || diagnostics[0].Primary == nil || diagnostics[0].Primary.Line != 4 {
+		t.Fatalf("non-mapping composition = (%#v, %#v)", composed, diagnostics)
+	}
+}
+
+func parseCompositionDocument(t *testing.T, sourceID, input string) *document.Node {
+	t.Helper()
+	parsed, diagnostics := parseSource(Bytes(sourceID, []byte(input)), sourceID, defaultParseLimits())
+	if len(diagnostics) != 0 {
+		t.Fatalf("parse diagnostics = %#v", diagnostics)
+	}
+	return parsed.document
+}
+
+func assertCompositionConflict(t *testing.T, diagnostics []Diagnostic, path string, sources []string) {
+	t.Helper()
+	if len(diagnostics) != 1 {
+		t.Fatalf("diagnostics = %#v, want one conflict", diagnostics)
+	}
+	diagnostic := diagnostics[0]
+	if diagnostic.Code != CodeComposeConflict || diagnostic.Path.String() != path || diagnostic.Primary == nil {
+		t.Fatalf("diagnostic = %#v, want compose conflict at %s", diagnostic, path)
+	}
+	locations := append([]Location{*diagnostic.Primary}, diagnostic.Related...)
+	gotSources := make([]string, len(locations))
+	for index, location := range locations {
+		gotSources[index] = location.SourceID
+	}
+	if !reflect.DeepEqual(gotSources, sources) {
+		t.Fatalf("claim sources = %#v, want %#v", gotSources, sources)
+	}
+}

internal/engine/composition_fuzz_test.go

@@ -0,0 +1,68 @@
+package engine
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+	yamladapter "gitea.maximumdirect.net/eric/ConfigKit/internal/yaml"
+)
+
+func FuzzCompositionAndOverlay(f *testing.F) {
+	for _, seed := range [][2]string{
+		{"{}\n", "{}\n"},
+		{"left: {value: one}\n", "right: [two]\n"},
+		{"shared: {left: one}\n", "shared: {right: two}\n"},
+		{"value: one\n", "value: two\n"},
+	} {
+		f.Add([]byte(seed[0]), []byte(seed[1]))
+	}
+
+	limits := yamladapter.Limits{Depth: 12, Nodes: 256, ParserDepth: 24}
+	f.Fuzz(func(t *testing.T, leftInput, rightInput []byte) {
+		if len(leftInput) > 4<<10 || len(rightInput) > 4<<10 {
+			return
+		}
+		left, leftIssues := yamladapter.Parse(bytes.NewReader(leftInput), "left", limits)
+		right, rightIssues := yamladapter.Parse(bytes.NewReader(rightInput), "right", limits)
+		if len(leftIssues) != 0 || len(rightIssues) != 0 {
+			return
+		}
+		leftBefore, rightBefore := document.Clone(left), document.Clone(right)
+
+		composed, diagnostics := composeDocuments(left, right)
+		if !reflect.DeepEqual(left, leftBefore) || !reflect.DeepEqual(right, rightBefore) {
+			t.Fatal("composition mutated an input document")
+		}
+		if len(diagnostics) == 0 {
+			reversed, reversedDiagnostics := composeDocuments(right, left)
+			if len(reversedDiagnostics) != 0 {
+				t.Fatalf("reversed composition failed: %#v", reversedDiagnostics)
+			}
+			if differences := compareConfigurationValues(composed.root, reversed.root); len(differences) != 0 {
+				t.Fatalf("composition order changed effective values: %#v", differences)
+			}
+			composed.root.Mapping = append(composed.root.Mapping, document.Entry{Key: "fuzz-detachment"})
+			if !reflect.DeepEqual(left, leftBefore) || !reflect.DeepEqual(right, rightBefore) {
+				t.Fatal("composition result aliases an input document")
+			}
+		}
+
+		base, baseDiagnostics := composeDocuments(left)
+		if len(baseDiagnostics) != 0 {
+			t.Fatalf("single accepted mapping did not compose: %#v", baseDiagnostics)
+		}
+		overlaid, overlayDiagnostics := overlayDocuments(base, right)
+		if len(overlayDiagnostics) != 0 {
+			t.Fatalf("accepted mappings did not overlay: %#v", overlayDiagnostics)
+		}
+		if !reflect.DeepEqual(left, leftBefore) || !reflect.DeepEqual(right, rightBefore) {
+			t.Fatal("overlay mutated an input document")
+		}
+		overlaid.root.Mapping = append(overlaid.root.Mapping, document.Entry{Key: "fuzz-detachment"})
+		if !reflect.DeepEqual(left, leftBefore) || !reflect.DeepEqual(right, rightBefore) {
+			t.Fatal("overlay result aliases an input document")
+		}
+	})
+}

internal/engine/decode.go

@@ -0,0 +1,470 @@
+package engine
+
+import (
+	"encoding"
+	"math"
+	"reflect"
+	"regexp"
+	"strconv"
+	"time"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+var integerPattern = regexp.MustCompile(`^-?(0|[1-9][0-9]*)$`)
+var unsignedIntegerPattern = regexp.MustCompile(`^(0|[1-9][0-9]*)$`)
+
+type decodeIssue struct {
+	code     Code
+	path     Path
+	message  string
+	location document.Location
+}
+
+type inputPresence struct {
+	null     bool
+	location document.Location
+}
+
+type decodedConfiguration struct {
+	value    reflect.Value
+	presence map[string]inputPresence
+	origins  map[string]Origin
+	baseline *document.Node
+	final    *document.Node
+}
+
+type decodeContext struct {
+	versionPath *Path
+}
+
+func decodeConfiguration(schema *schemaDescriptor, defaults reflect.Value, input *document.Node) (decodedConfiguration, []decodeIssue) {
+	return decodeConfigurationWithContext(schema, defaults, input, decodeContext{})
+}
+
+func decodeConfigurationWithContext(schema *schemaDescriptor, defaults reflect.Value, input *document.Node, context decodeContext) (decodedConfiguration, []decodeIssue) {
+	if schema == nil || schema.root == nil || !defaults.IsValid() || defaults.Type() != schema.root.typeOf {
+		return decodedConfiguration{}, []decodeIssue{{code: CodeSchemaUnsupportedType, message: "configuration defaults do not match the schema"}}
+	}
+	baseline, projectionIssue := projectConfiguration(schema, defaults, defaultProjectionLimits())
+	if projectionIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(projectionIssue)}
+	}
+	working, cloneIssue := cloneConfiguration(schema, defaults, defaultProjectionLimits())
+	if cloneIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(cloneIssue)}
+	}
+
+	presence := make(map[string]inputPresence)
+	if input != nil {
+		collectPresence(input, Path{}, presence)
+		decoded, issues := decodeValue(input, working, schema.root, Path{}, schema, context)
+		if len(issues) != 0 {
+			return decodedConfiguration{}, issues
+		}
+		working = decoded
+	}
+	final, projectionIssue := projectConfiguration(schema, working, defaultProjectionLimits())
+	if projectionIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(projectionIssue)}
+	}
+	origins := make(map[string]Origin)
+	collectOrigins(final, Path{}, presence, origins)
+	return decodedConfiguration{
+		value:    working,
+		presence: presence,
+		origins:  origins,
+		baseline: baseline,
+		final:    final,
+	}, nil
+}
+
+func decodeValue(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind == document.Null {
+		switch descriptor.kind {
+		case descriptorPointer, descriptorMap, descriptorSlice, descriptorDynamic:
+			return reflect.Zero(descriptor.typeOf), nil
+		case descriptorSecret:
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeSecretRequired, path, node, "required secret reference cannot be null")}
+		default:
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeNull, path, node, "null is not allowed for this configuration type")}
+		}
+	}
+	if descriptor.kind == descriptorPointer {
+		var elementBase reflect.Value
+		if base.IsNil() {
+			elementBase = reflect.Zero(descriptor.typeOf.Elem())
+		} else {
+			elementBase = base.Elem()
+		}
+		decoded, issues := decodeValue(node, elementBase, descriptor.element, path, schema, context)
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		result := reflect.New(descriptor.typeOf.Elem())
+		result.Elem().Set(decoded)
+		return result, nil
+	}
+
+	switch descriptor.kind {
+	case descriptorStruct:
+		return decodeStruct(node, base, descriptor, path, schema, context)
+	case descriptorMap:
+		return decodeMap(node, base, descriptor, path, schema, context)
+	case descriptorSlice:
+		return decodeSlice(node, descriptor, path, schema, context)
+	case descriptorArray:
+		return decodeArray(node, descriptor, path, schema, context)
+	case descriptorDynamic:
+		return decodeDynamic(node, base, path, schema, context)
+	case descriptorString:
+		if node.Kind != document.String && !(pathMatches(context.versionPath, path) && isIntegerVersion(node)) {
+			return typeMismatch(path, node, "string")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetString(node.Text)
+		return result, nil
+	case descriptorBoolean:
+		if node.Kind != document.Boolean {
+			return typeMismatch(path, node, "boolean")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetBool(node.Text == "true")
+		return result, nil
+	case descriptorSigned:
+		if node.Kind != document.Number || !integerPattern.MatchString(node.Text) {
+			return typeMismatch(path, node, "integer")
+		}
+		value, err := strconv.ParseInt(node.Text, 10, descriptor.typeOf.Bits())
+		if err != nil {
+			return rangeFailure(path, node, "integer")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetInt(value)
+		return result, nil
+	case descriptorUnsigned:
+		if node.Kind != document.Number || !unsignedIntegerPattern.MatchString(node.Text) {
+			return typeMismatch(path, node, "unsigned integer")
+		}
+		value, err := strconv.ParseUint(node.Text, 10, descriptor.typeOf.Bits())
+		if err != nil {
+			return rangeFailure(path, node, "unsigned integer")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetUint(value)
+		return result, nil
+	case descriptorFloat:
+		if node.Kind != document.Number {
+			return typeMismatch(path, node, "number")
+		}
+		value, err := strconv.ParseFloat(node.Text, descriptor.typeOf.Bits())
+		if err != nil || math.IsNaN(value) || math.IsInf(value, 0) {
+			return rangeFailure(path, node, "number")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetFloat(value)
+		return result, nil
+	case descriptorDuration:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "duration string")
+		}
+		value, err := time.ParseDuration(node.Text)
+		if err != nil {
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeDuration, path, node, "duration string is invalid")}
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetInt(int64(value))
+		return result, nil
+	case descriptorSecret:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "secret environment name")
+		}
+		return schema.secrets.Make(SecretState{Name: node.Text, Specified: true}), nil
+	case descriptorText:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "text string")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		unmarshaler := result.Addr().Interface().(encoding.TextUnmarshaler)
+		if err := unmarshaler.UnmarshalText([]byte(node.Text)); err != nil {
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeText, path, node, "text value is invalid for its configuration type")}
+		}
+		return result, nil
+	default:
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeSchemaUnsupportedType, path, node, "configuration type is not supported")}
+	}
+}
+
+func decodeStruct(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Mapping {
+		return typeMismatch(path, node, "mapping")
+	}
+	result := reflect.New(descriptor.typeOf).Elem()
+	result.Set(base)
+	var issues []decodeIssue
+	for _, entry := range node.Mapping {
+		childPath := path.Key(entry.Key)
+		if position, ok := descriptor.fieldByName[entry.Key]; ok {
+			field := descriptor.fields[position]
+			target, ok := fieldForDecode(result, field.index, true)
+			if !ok {
+				issues = append(issues, decodeIssue{code: CodeSchemaUnsupportedType, path: childPath, message: "configuration field could not be addressed", location: entry.ValueLocation})
+				continue
+			}
+			decoded, fieldIssues := decodeValue(entry.Value, target, field.descriptor, childPath, schema, context)
+			if len(fieldIssues) != 0 {
+				issues = append(issues, fieldIssues...)
+				continue
+			}
+			target.Set(decoded)
+			continue
+		}
+		if descriptor.inlineMap != nil {
+			if issue := decodeInlineMapEntry(result, *descriptor.inlineMap, entry, childPath, schema, context); issue != nil {
+				issues = append(issues, issue...)
+			}
+			continue
+		}
+		issues = append(issues, decodeIssue{code: CodeDecodeUnknownField, path: childPath, message: "configuration field is not declared", location: entry.KeyLocation})
+	}
+	return result, issues
+}
+
+func decodeInlineMapEntry(target reflect.Value, field fieldDescriptor, entry document.Entry, path Path, schema *schemaDescriptor, context decodeContext) []decodeIssue {
+	mapValue, ok := fieldForDecode(target, field.index, true)
+	if !ok || mapValue.Kind() != reflect.Map {
+		return []decodeIssue{{code: CodeSchemaInline, path: path, message: "inline map could not be addressed", location: entry.KeyLocation}}
+	}
+	if mapValue.IsNil() {
+		mapValue.Set(reflect.MakeMap(mapValue.Type()))
+	}
+	key := reflect.New(mapValue.Type().Key()).Elem()
+	key.SetString(entry.Key)
+	base := mapValue.MapIndex(key)
+	if !base.IsValid() {
+		base = reflect.Zero(mapValue.Type().Elem())
+	}
+	decoded, issues := decodeValue(entry.Value, base, field.descriptor.element, path, schema, context)
+	if len(issues) == 0 {
+		mapValue.SetMapIndex(key, decoded)
+	}
+	return issues
+}
+
+func decodeMap(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Mapping {
+		return typeMismatch(path, node, "mapping")
+	}
+	result := base
+	if result.IsNil() {
+		result = reflect.MakeMap(descriptor.typeOf)
+	}
+	var issues []decodeIssue
+	for _, entry := range node.Mapping {
+		key := reflect.New(descriptor.typeOf.Key()).Elem()
+		key.SetString(entry.Key)
+		entryBase := result.MapIndex(key)
+		if !entryBase.IsValid() {
+			entryBase = reflect.Zero(descriptor.typeOf.Elem())
+		}
+		decoded, entryIssues := decodeValue(entry.Value, entryBase, descriptor.element, path.Key(entry.Key), schema, context)
+		if len(entryIssues) != 0 {
+			issues = append(issues, entryIssues...)
+			continue
+		}
+		result.SetMapIndex(key, decoded)
+	}
+	return result, issues
+}
+
+func decodeSlice(node *document.Node, descriptor *typeDescriptor, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Sequence {
+		return typeMismatch(path, node, "sequence")
+	}
+	result := reflect.MakeSlice(descriptor.typeOf, len(node.Sequence), len(node.Sequence))
+	var issues []decodeIssue
+	for i, child := range node.Sequence {
+		decoded, childIssues := decodeValue(child, reflect.Zero(descriptor.typeOf.Elem()), descriptor.element, path.Index(i), schema, context)
+		if len(childIssues) != 0 {
+			issues = append(issues, childIssues...)
+			continue
+		}
+		result.Index(i).Set(decoded)
+	}
+	return result, issues
+}
+
+func decodeArray(node *document.Node, descriptor *typeDescriptor, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Sequence {
+		return typeMismatch(path, node, "sequence")
+	}
+	if len(node.Sequence) != descriptor.length {
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeArrayLength, path, node, "configuration array has the wrong length")}
+	}
+	result := reflect.New(descriptor.typeOf).Elem()
+	var issues []decodeIssue
+	for i, child := range node.Sequence {
+		decoded, childIssues := decodeValue(child, reflect.Zero(descriptor.typeOf.Elem()), descriptor.element, path.Index(i), schema, context)
+		if len(childIssues) != 0 {
+			issues = append(issues, childIssues...)
+			continue
+		}
+		result.Index(i).Set(decoded)
+	}
+	return result, issues
+}
+
+func decodeDynamic(node *document.Node, base reflect.Value, path Path, schema *schemaDescriptor, context decodeContext) (reflect.Value, []decodeIssue) {
+	if node.Kind == document.Mapping && base.IsValid() && !base.IsNil() {
+		concrete := base.Elem()
+		operation := valueOperation{schema: schema}
+		descriptor, issue := operation.dynamicDescriptor(concrete.Type(), path)
+		if issue == nil && acceptsMapping(descriptor) {
+			decoded, issues := decodeValue(node, concrete, descriptor, path, schema, context)
+			if len(issues) != 0 {
+				return reflect.Value{}, issues
+			}
+			result := reflect.New(base.Type()).Elem()
+			result.Set(decoded)
+			return result, nil
+		}
+	}
+	var value any
+	switch node.Kind {
+	case document.Null:
+		return reflect.Zero(base.Type()), nil
+	case document.String:
+		value = node.Text
+	case document.Boolean:
+		value = node.Text == "true"
+	case document.Number:
+		if integerPattern.MatchString(node.Text) {
+			parsed, err := strconv.ParseInt(node.Text, 10, 64)
+			if err != nil {
+				return rangeFailure(path, node, "dynamic integer")
+			}
+			value = parsed
+		} else {
+			parsed, err := strconv.ParseFloat(node.Text, 64)
+			if err != nil || math.IsNaN(parsed) || math.IsInf(parsed, 0) {
+				return rangeFailure(path, node, "dynamic number")
+			}
+			value = parsed
+		}
+	case document.Sequence:
+		sequence := make([]any, len(node.Sequence))
+		var issues []decodeIssue
+		for i, child := range node.Sequence {
+			decoded, childIssues := decodeDynamic(child, reflect.Zero(reflect.TypeFor[any]()), path.Index(i), schema, context)
+			if len(childIssues) != 0 {
+				issues = append(issues, childIssues...)
+				continue
+			}
+			sequence[i] = decoded.Interface()
+		}
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		value = sequence
+	case document.Mapping:
+		mapping := make(map[string]any, len(node.Mapping))
+		var issues []decodeIssue
+		for _, entry := range node.Mapping {
+			decoded, childIssues := decodeDynamic(entry.Value, reflect.Zero(reflect.TypeFor[any]()), path.Key(entry.Key), schema, context)
+			if len(childIssues) != 0 {
+				issues = append(issues, childIssues...)
+				continue
+			}
+			mapping[entry.Key] = decoded.Interface()
+		}
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		value = mapping
+	default:
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeType, path, node, "dynamic configuration value has an unsupported kind")}
+	}
+	result := reflect.New(base.Type()).Elem()
+	if value != nil {
+		result.Set(reflect.ValueOf(value))
+	}
+	return result, nil
+}
+
+func acceptsMapping(descriptor *typeDescriptor) bool {
+	for descriptor != nil && descriptor.kind == descriptorPointer {
+		descriptor = descriptor.element
+	}
+	return descriptor != nil && (descriptor.kind == descriptorStruct || descriptor.kind == descriptorMap || descriptor.kind == descriptorDynamic)
+}
+
+func fieldForDecode(root reflect.Value, index []int, allocate bool) (reflect.Value, bool) {
+	current := root
+	for position, fieldIndex := range index {
+		if current.Kind() != reflect.Struct {
+			return reflect.Value{}, false
+		}
+		current = current.Field(fieldIndex)
+		if position == len(index)-1 {
+			return current, current.CanSet()
+		}
+		for current.Kind() == reflect.Pointer {
+			if current.IsNil() {
+				if !allocate || !current.CanSet() {
+					return reflect.Value{}, false
+				}
+				current.Set(reflect.New(current.Type().Elem()))
+			}
+			current = current.Elem()
+		}
+	}
+	return reflect.Value{}, false
+}
+
+func collectPresence(node *document.Node, path Path, presence map[string]inputPresence) {
+	presence[path.String()] = inputPresence{null: node.Kind == document.Null, location: node.Location}
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			collectPresence(entry.Value, path.Key(entry.Key), presence)
+		}
+	case document.Sequence:
+		for i, child := range node.Sequence {
+			collectPresence(child, path.Index(i), presence)
+		}
+	}
+}
+
+func collectOrigins(node *document.Node, path Path, presence map[string]inputPresence, origins map[string]Origin) {
+	if input, ok := presence[path.String()]; ok {
+		origins[path.String()] = Origin{Layer: LayerBase, Locations: []Location{{SourceID: input.location.SourceID, Line: input.location.Line, Column: input.location.Column}}}
+	} else {
+		origins[path.String()] = Origin{Layer: LayerDefault}
+	}
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			collectOrigins(entry.Value, path.Key(entry.Key), presence, origins)
+		}
+	case document.Sequence:
+		for i, child := range node.Sequence {
+			collectOrigins(child, path.Index(i), presence, origins)
+		}
+	}
+}
+
+func decodeIssueFromProjection(issue *projectionIssue) decodeIssue {
+	return decodeIssue{code: issue.code, path: issue.path.clone(), message: issue.message}
+}
+
+func newDecodeIssue(code Code, path Path, node *document.Node, message string) decodeIssue {
+	return decodeIssue{code: code, path: path.clone(), message: message, location: node.Location}
+}
+
+func typeMismatch(path Path, node *document.Node, expected string) (reflect.Value, []decodeIssue) {
+	return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeType, path, node, "configuration value must be a "+expected)}
+}
+
+func rangeFailure(path Path, node *document.Node, expected string) (reflect.Value, []decodeIssue) {
+	return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeRange, path, node, expected+" is outside the supported range")}
+}

internal/engine/decode_test.go

@@ -0,0 +1,312 @@
+package engine
+
+import (
+	"errors"
+	"math"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type namedSmall int8
+
+type validatedText string
+
+func (value validatedText) MarshalText() ([]byte, error) {
+	return []byte(value), nil
+}
+
+func (value *validatedText) UnmarshalText(text []byte) error {
+	if string(text) == "bad-secret-canary" {
+		return errors.New("CANARY_TEXT_ERROR: bad-secret-canary")
+	}
+	*value = validatedText(text)
+	return nil
+}
+
+func TestDecodeAppliesInputOverDetachedDefaults(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		A string `yaml:"a"`
+		B string `yaml:"b"`
+	}
+	type config struct {
+		Enabled      bool              `yaml:"enabled"`
+		Workers      int               `yaml:"workers"`
+		Label        string            `yaml:"label"`
+		Nested       nested            `yaml:"nested"`
+		EmptyMapping nested            `yaml:"empty_mapping"`
+		Objects      map[string]nested `yaml:"objects"`
+		Sequence     []string          `yaml:"sequence"`
+		Replacement  []string          `yaml:"replacement"`
+		Pointer      *nested           `yaml:"pointer"`
+		NilPointer   *nested           `yaml:"nil_pointer"`
+		Nullable     map[string]string `yaml:"nullable"`
+		Dynamic      any               `yaml:"dynamic"`
+		DynamicShape any               `yaml:"dynamic_shape"`
+		DynamicNull  any               `yaml:"dynamic_null"`
+		Fixed        [2]int            `yaml:"fixed"`
+		Small        namedSmall        `yaml:"small"`
+		Delay        time.Duration     `yaml:"delay"`
+		Custom       validatedText     `yaml:"custom"`
+	}
+	defaults := config{
+		Enabled:      true,
+		Workers:      4,
+		Label:        "default",
+		Nested:       nested{A: "keep", B: "before"},
+		EmptyMapping: nested{A: "keep-empty", B: "keep-empty"},
+		Objects: map[string]nested{
+			"existing": {A: "keep-map", B: "before"},
+		},
+		Sequence:     []string{"default"},
+		Replacement:  []string{"default"},
+		Pointer:      &nested{A: "keep-pointer", B: "before"},
+		Nullable:     map[string]string{"default": "value"},
+		Dynamic:      map[string]any{"keep": "default", "count": int64(4)},
+		DynamicShape: nested{A: "keep-dynamic", B: "before"},
+		DynamicNull:  "default",
+		Fixed:        [2]int{1, 2},
+		Small:        7,
+		Delay:        time.Second,
+		Custom:       "default",
+	}
+	input := `
+enabled: false
+workers: 0
+label: ""
+nested: {b: changed}
+empty_mapping: {}
+objects:
+  existing: {b: changed}
+  new: {b: added}
+sequence: []
+replacement: [one, two]
+pointer: {b: changed}
+nil_pointer: {b: added}
+nullable: null
+dynamic: {count: 0, fraction: 1.5}
+dynamic_shape: {b: changed}
+dynamic_null: null
+fixed: [3, 4]
+small: -8
+delay: 1.5s
+custom: accepted
+`
+	schema := mustSchemaFor[config](t)
+	documentRoot := parseDocumentForDecode(t, input)
+	decoded, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), documentRoot)
+	if len(issues) != 0 {
+		t.Fatalf("decode issues = %#v", issues)
+	}
+	got := decoded.value.Interface().(config)
+	if got.Enabled || got.Workers != 0 || got.Label != "" {
+		t.Fatalf("explicit zero values lost: %#v", got)
+	}
+	if got.Nested != (nested{A: "keep", B: "changed"}) || got.EmptyMapping != defaults.EmptyMapping {
+		t.Fatalf("mapping defaults = %#v / %#v", got.Nested, got.EmptyMapping)
+	}
+	if got.Objects["existing"] != (nested{A: "keep-map", B: "changed"}) || got.Objects["new"] != (nested{B: "added"}) {
+		t.Fatalf("map defaults = %#v", got.Objects)
+	}
+	if got.Sequence == nil || len(got.Sequence) != 0 || !reflect.DeepEqual(got.Replacement, []string{"one", "two"}) {
+		t.Fatalf("sequence replacement = %#v / %#v", got.Sequence, got.Replacement)
+	}
+	if got.Pointer == defaults.Pointer || *got.Pointer != (nested{A: "keep-pointer", B: "changed"}) || got.NilPointer == nil || *got.NilPointer != (nested{B: "added"}) {
+		t.Fatalf("pointer defaults = %#v / %#v", got.Pointer, got.NilPointer)
+	}
+	if got.Nullable != nil || got.DynamicNull != nil {
+		t.Fatalf("null values = %#v / %#v", got.Nullable, got.DynamicNull)
+	}
+	dynamic := got.Dynamic.(map[string]any)
+	if dynamic["keep"] != "default" || dynamic["count"] != int64(0) || dynamic["fraction"] != float64(1.5) {
+		t.Fatalf("dynamic mapping = %#v", dynamic)
+	}
+	if got.DynamicShape != (nested{A: "keep-dynamic", B: "changed"}) {
+		t.Fatalf("dynamic concrete mapping = %#v", got.DynamicShape)
+	}
+	if got.Fixed != [2]int{3, 4} || got.Small != -8 || got.Delay != 1500*time.Millisecond || got.Custom != "accepted" {
+		t.Fatalf("scalar decoding = %#v", got)
+	}
+
+	for _, path := range []Path{Keys(), Keys("enabled"), Keys("nested"), Keys("nested", "b"), Keys("empty_mapping")} {
+		if _, ok := decoded.presence[path.String()]; !ok {
+			t.Errorf("explicit path %q missing", path.String())
+		}
+	}
+	if _, ok := decoded.presence[Keys("nested", "a").String()]; ok {
+		t.Fatal("parent mapping made omitted child explicit")
+	}
+	if decoded.origins[Keys("nested", "a").String()].Layer != LayerDefault || decoded.origins[Keys("nested", "b").String()].Layer != LayerBase {
+		t.Fatalf("origins = %#v", decoded.origins)
+	}
+	if decoded.origins[Keys("nested", "b").String()].Locations[0].Line == 0 {
+		t.Fatal("input origin lost source coordinates")
+	}
+
+	defaults.Objects["existing"] = nested{A: "mutated"}
+	defaults.Pointer.B = "mutated"
+	defaults.Sequence[0] = "mutated"
+	if got.Objects["existing"].A != "keep-map" || got.Pointer.B != "changed" || len(got.Sequence) != 0 {
+		t.Fatal("decoded value aliases defaults")
+	}
+	got.Pointer.B = "caller mutation"
+	if mappingValue(t, mappingValue(t, decoded.final, "pointer"), "b").Text != "changed" {
+		t.Fatal("final snapshot aliases returned typed value")
+	}
+	if mappingValue(t, mappingValue(t, decoded.baseline, "nested"), "b").Text != "before" {
+		t.Fatal("baseline snapshot was mutated by decode")
+	}
+}
+
+func TestDecodeDefaultsOnlyAndRepeatedResultsAreIndependent(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Values map[string][]string `yaml:"values"`
+	}
+	defaults := config{Values: map[string][]string{"one": {"a"}}}
+	schema := mustSchemaFor[config](t)
+	first, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), nil)
+	if len(issues) != 0 {
+		t.Fatal(issues)
+	}
+	second, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), nil)
+	if len(issues) != 0 {
+		t.Fatal(issues)
+	}
+	firstValue := first.value.Interface().(config)
+	secondValue := second.value.Interface().(config)
+	firstValue.Values["one"][0] = "changed"
+	if secondValue.Values["one"][0] != "a" || defaults.Values["one"][0] != "a" {
+		t.Fatal("repeated defaults-only results share aliases")
+	}
+	if len(first.presence) != 0 || first.origins[Keys("values", "one").String()].Layer != LayerDefault {
+		t.Fatalf("defaults-only metadata = %#v / %#v", first.presence, first.origins)
+	}
+}
+
+func TestDecodeCollectsIndependentTypeAndShapeFailures(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		Known int `yaml:"known"`
+	}
+	type config struct {
+		Small    int8          `yaml:"small"`
+		Unsigned uint8         `yaml:"unsigned"`
+		Number   float32       `yaml:"number"`
+		Text     string        `yaml:"text"`
+		Flag     bool          `yaml:"flag"`
+		Delay    time.Duration `yaml:"delay"`
+		Fixed    [2]int        `yaml:"fixed"`
+		Nested   nested        `yaml:"nested"`
+		Custom   validatedText `yaml:"custom"`
+		Dynamic  any           `yaml:"dynamic"`
+	}
+	input := `
+small: 128
+unsigned: -1
+number: 1e999
+text: 3
+flag: "true"
+delay: 10
+fixed: [1]
+nested: {first_unknown: 1, second_unknown: 2}
+custom: bad-secret-canary
+dynamic: 9223372036854775808
+`
+	schema := mustSchemaFor[config](t)
+	_, issues := decodeConfiguration(schema, reflect.ValueOf(config{Custom: "ok"}), parseDocumentForDecode(t, input))
+	if len(issues) != 11 {
+		t.Fatalf("issues = %d: %#v", len(issues), issues)
+	}
+	want := map[string]Code{
+		"/small":                 CodeDecodeRange,
+		"/unsigned":              CodeDecodeType,
+		"/number":                CodeDecodeRange,
+		"/text":                  CodeDecodeType,
+		"/flag":                  CodeDecodeType,
+		"/delay":                 CodeDecodeType,
+		"/fixed":                 CodeDecodeArrayLength,
+		"/nested/first_unknown":  CodeDecodeUnknownField,
+		"/nested/second_unknown": CodeDecodeUnknownField,
+		"/custom":                CodeDecodeText,
+		"/dynamic":               CodeDecodeRange,
+	}
+	for _, issue := range issues {
+		if wantCode, ok := want[issue.path.String()]; !ok || wantCode != issue.code {
+			t.Errorf("unexpected issue %#v", issue)
+		}
+		if issue.location.Line == 0 {
+			t.Errorf("issue lost input location: %#v", issue)
+		}
+		if strings.Contains(issue.message, "CANARY") || strings.Contains(issue.message, "bad-secret") {
+			t.Errorf("issue exposed value: %#v", issue)
+		}
+	}
+}
+
+func TestDecodeNullabilityAndNestedMapStrictness(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		Value int `yaml:"value"`
+	}
+	type config struct {
+		Scalar int               `yaml:"scalar"`
+		Object nested            `yaml:"object"`
+		Array  [1]int            `yaml:"array"`
+		Map    map[string]nested `yaml:"map"`
+	}
+	input := "scalar: null\nobject: null\narray: null\nmap:\n  item: {unknown: 1}\n"
+	_, issues := decodeConfiguration(mustSchemaFor[config](t), reflect.ValueOf(config{}), parseDocumentForDecode(t, input))
+	want := map[string]Code{
+		"/scalar":           CodeDecodeNull,
+		"/object":           CodeDecodeNull,
+		"/array":            CodeDecodeNull,
+		"/map/item/unknown": CodeDecodeUnknownField,
+	}
+	if len(issues) != len(want) {
+		t.Fatalf("issues = %#v", issues)
+	}
+	for _, issue := range issues {
+		if want[issue.path.String()] != issue.code {
+			t.Errorf("issue = %#v", issue)
+		}
+	}
+}
+
+func TestDecodeRejectsInvalidDefaultsBeforeApplyingInput(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Name   string         `yaml:"name"`
+		Extras map[string]any `yaml:",inline"`
+		Float  float64        `yaml:"float"`
+	}
+	schema := mustSchemaFor[config](t)
+	for name, defaults := range map[string]config{
+		"inline collision": {Name: "declared", Extras: map[string]any{"name": "duplicate"}},
+		"non-finite":       {Float: math.NaN()},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if _, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), parseDocumentForDecode(t, "{}\n")); len(issues) != 1 || !strings.HasPrefix(string(issues[0].code), "schema.") {
+				t.Fatalf("issues = %#v", issues)
+			}
+		})
+	}
+}
+
+func parseDocumentForDecode(t *testing.T, input string) *document.Node {
+	t.Helper()
+	parsed, diagnostics := parseSource(Bytes("decode.yml", []byte(input)), "source-1", defaultParseLimits())
+	if len(diagnostics) != 0 {
+		t.Fatalf("parse diagnostics = %#v", diagnostics)
+	}
+	return parsed.document
+}

internal/engine/diagnostic.go

@@ -0,0 +1,248 @@
+package engine
+
+import (
+	"cmp"
+	"fmt"
+	"io"
+	"slices"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// LoadError reports safe structured diagnostics for a failed configuration load.
+// It intentionally does not expose or unwrap parser and application errors.
+type LoadError struct {
+	diagnostics []Diagnostic
+	sources     []SourceInfo
+}
+
+// Error implements error without rendering diagnostic messages or input values.
+func (e *LoadError) Error() string {
+	if e == nil {
+		return "configkit: configuration load failed"
+	}
+	count := 0
+	for _, diagnostic := range e.diagnostics {
+		if diagnostic.Severity == SeverityError {
+			count++
+		}
+	}
+	if count == 1 {
+		return "configkit: configuration load failed with 1 error"
+	}
+	return fmt.Sprintf("configkit: configuration load failed with %d errors", count)
+}
+
+// Diagnostics returns a deep copy of the error's canonical diagnostics.
+func (e *LoadError) Diagnostics() []Diagnostic {
+	if e == nil {
+		return nil
+	}
+	return cloneDiagnostics(e.diagnostics)
+}
+
+// Sources returns a deep copy of sources discovered before loading failed.
+func (e *LoadError) Sources() []SourceInfo {
+	if e == nil {
+		return nil
+	}
+	return cloneSourceInfos(e.sources)
+}
+
+// WriteDiagnostics writes diagnostics in canonical order. It escapes terminal
+// control characters and propagates writer errors, including short writes.
+func WriteDiagnostics(output io.Writer, diagnostics []Diagnostic) error {
+	canonical := canonicalDiagnostics(diagnostics)
+	for _, diagnostic := range canonical {
+		if err := writeDiagnostic(output, diagnostic); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+type diagnosticAccumulator struct {
+	diagnostics []Diagnostic
+	sources     []SourceInfo
+}
+
+func (a *diagnosticAccumulator) add(diagnostics ...Diagnostic) {
+	for _, diagnostic := range diagnostics {
+		a.diagnostics = append(a.diagnostics, cloneDiagnostic(diagnostic))
+	}
+}
+
+func (a *diagnosticAccumulator) loadError() *LoadError {
+	return &LoadError{
+		diagnostics: canonicalDiagnostics(a.diagnostics),
+		sources:     cloneSourceInfos(a.sources),
+	}
+}
+
+func canonicalDiagnostics(diagnostics []Diagnostic) []Diagnostic {
+	canonical := cloneDiagnostics(diagnostics)
+	for i := range canonical {
+		slices.SortFunc(canonical[i].Related, compareLocation)
+	}
+	slices.SortFunc(canonical, compareDiagnostic)
+	return canonical
+}
+
+func compareDiagnostic(left, right Diagnostic) int {
+	if order := compareOptionalLocation(left.Primary, right.Primary); order != 0 {
+		return order
+	}
+	if order := cmp.Compare(left.Path.String(), right.Path.String()); order != 0 {
+		return order
+	}
+	if order := cmp.Compare(left.Code, right.Code); order != 0 {
+		return order
+	}
+	if order := cmp.Compare(left.Severity, right.Severity); order != 0 {
+		return order
+	}
+	if order := cmp.Compare(left.Message, right.Message); order != 0 {
+		return order
+	}
+	return compareLocations(left.Related, right.Related)
+}
+
+func compareOptionalLocation(left, right *Location) int {
+	if left == nil && right == nil {
+		return 0
+	}
+	if left == nil {
+		return -1
+	}
+	if right == nil {
+		return 1
+	}
+	return compareLocation(*left, *right)
+}
+
+func compareLocations(left, right []Location) int {
+	for i := 0; i < min(len(left), len(right)); i++ {
+		if order := compareLocation(left[i], right[i]); order != 0 {
+			return order
+		}
+	}
+	return cmp.Compare(len(left), len(right))
+}
+
+func compareLocation(left, right Location) int {
+	if order := compareSourceID(left.SourceID, right.SourceID); order != 0 {
+		return order
+	}
+	if order := cmp.Compare(left.Line, right.Line); order != 0 {
+		return order
+	}
+	return cmp.Compare(left.Column, right.Column)
+}
+
+func compareSourceID(left, right string) int {
+	leftOrder, leftOK := sourceSequence(left)
+	rightOrder, rightOK := sourceSequence(right)
+	if leftOK && rightOK {
+		return cmp.Compare(leftOrder, rightOrder)
+	}
+	return cmp.Compare(left, right)
+}
+
+func sourceSequence(sourceID string) (int, bool) {
+	const prefix = "source-"
+	if !strings.HasPrefix(sourceID, prefix) {
+		return 0, false
+	}
+	value, err := strconv.Atoi(strings.TrimPrefix(sourceID, prefix))
+	if err != nil || value < 1 {
+		return 0, false
+	}
+	return value, true
+}
+
+func writeDiagnostic(output io.Writer, diagnostic Diagnostic) error {
+	severity := diagnostic.Severity
+	if severity == "" {
+		severity = SeverityError
+	}
+	path := diagnostic.Path.String()
+	if path == "" {
+		path = "<root>"
+	}
+
+	var b strings.Builder
+	b.WriteString(escapeControls(string(severity)))
+	if diagnostic.Code != "" {
+		b.WriteString(" [")
+		b.WriteString(escapeControls(string(diagnostic.Code)))
+		b.WriteByte(']')
+	}
+	b.WriteByte(' ')
+	b.WriteString(escapeControls(path))
+	if diagnostic.Primary != nil {
+		b.WriteString(" (")
+		writeLocationText(&b, *diagnostic.Primary)
+		b.WriteByte(')')
+	}
+	if diagnostic.Message != "" {
+		b.WriteString(": ")
+		b.WriteString(escapeControls(diagnostic.Message))
+	}
+	b.WriteByte('\n')
+	for _, related := range diagnostic.Related {
+		b.WriteString("  related: ")
+		writeLocationText(&b, related)
+		b.WriteByte('\n')
+	}
+	return writeString(output, b.String())
+}
+
+func writeLocationText(output *strings.Builder, location Location) {
+	label := location.SourceID
+	if label == "" {
+		label = "<synthetic>"
+	}
+	output.WriteString(escapeControls(label))
+	if location.Line > 0 {
+		output.WriteByte(':')
+		output.WriteString(strconv.Itoa(location.Line))
+		if location.Column > 0 {
+			output.WriteByte(':')
+			output.WriteString(strconv.Itoa(location.Column))
+		}
+	}
+}
+
+func writeString(output io.Writer, value string) error {
+	written, err := io.WriteString(output, value)
+	if err != nil {
+		return err
+	}
+	if written != len(value) {
+		return io.ErrShortWrite
+	}
+	return nil
+}
+
+func escapeControls(value string) string {
+	var b strings.Builder
+	for _, r := range value {
+		if unicode.IsControl(r) {
+			quoted := strconv.QuoteRune(r)
+			b.WriteString(quoted[1 : len(quoted)-1])
+			continue
+		}
+		b.WriteRune(r)
+	}
+	return b.String()
+}
+
+func hasErrors(diagnostics []Diagnostic) bool {
+	for _, diagnostic := range diagnostics {
+		if diagnostic.Severity == SeverityError {
+			return true
+		}
+	}
+	return false
+}

internal/engine/diagnostic_test.go

@@ -0,0 +1,143 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestDiagnosticsAreCanonicalAndDetached(t *testing.T) {
+	t.Parallel()
+
+	diagnostics := []Diagnostic{
+		{
+			Code:     "decode.type",
+			Severity: SeverityError,
+			Path:     Keys("later"),
+			Message:  "later",
+			Primary:  &Location{SourceID: "source-10", Line: 1, Column: 1},
+		},
+		{
+			Code:     "schema.invalid",
+			Severity: SeverityError,
+			Path:     Keys("root"),
+			Message:  "source-less",
+		},
+		{
+			Code:     "decode.type",
+			Severity: SeverityError,
+			Path:     Keys("earlier"),
+			Message:  "earlier",
+			Primary:  &Location{SourceID: "source-2", Line: 3, Column: 4},
+			Related: []Location{
+				{SourceID: "source-10", Line: 1, Column: 1},
+				{SourceID: "source-2", Line: 9, Column: 1},
+			},
+		},
+	}
+
+	var forward bytes.Buffer
+	if err := WriteDiagnostics(&forward, diagnostics); err != nil {
+		t.Fatal(err)
+	}
+	reversed := []Diagnostic{diagnostics[2], diagnostics[1], diagnostics[0]}
+	var backward bytes.Buffer
+	if err := WriteDiagnostics(&backward, reversed); err != nil {
+		t.Fatal(err)
+	}
+	if forward.String() != backward.String() {
+		t.Fatalf("rendering depends on submission order:\n%s\n---\n%s", forward.String(), backward.String())
+	}
+	lines := strings.Split(forward.String(), "\n")
+	if !strings.Contains(lines[0], "source-less") || !strings.Contains(lines[1], "source-2:3:4") {
+		t.Fatalf("unexpected canonical order:\n%s", forward.String())
+	}
+	if !strings.Contains(lines[2], "source-2:9:1") || !strings.Contains(lines[3], "source-10:1:1") {
+		t.Fatalf("related locations not canonical:\n%s", forward.String())
+	}
+
+	accumulator := diagnosticAccumulator{
+		sources: []SourceInfo{{
+			ID:           "source-1",
+			Label:        "config.yml",
+			ImportedFrom: &Location{SourceID: "source-0", Line: 1},
+		}},
+	}
+	accumulator.add(diagnostics...)
+	loadErr := accumulator.loadError()
+	var found *LoadError
+	if !errors.As(error(loadErr), &found) || found != loadErr {
+		t.Fatal("errors.As did not find LoadError")
+	}
+
+	first := loadErr.Diagnostics()
+	first[1].Primary.SourceID = "mutated"
+	first[1].Path.segments[0].key = "mutated"
+	first[1].Related[0].SourceID = "mutated"
+	second := loadErr.Diagnostics()
+	if second[1].Primary.SourceID != "source-2" || second[1].Path.String() != "/earlier" || second[1].Related[0].SourceID != "source-2" {
+		t.Fatal("Diagnostics returned aliased records")
+	}
+	sources := loadErr.Sources()
+	sources[0].ImportedFrom.SourceID = "mutated"
+	if loadErr.Sources()[0].ImportedFrom.SourceID != "source-0" {
+		t.Fatal("Sources returned aliased records")
+	}
+	if got := loadErr.Error(); got != "configkit: configuration load failed with 3 errors" {
+		t.Fatalf("Error() = %q", got)
+	}
+}
+
+func TestWriteDiagnosticsEscapesControls(t *testing.T) {
+	t.Parallel()
+
+	diagnostic := Diagnostic{
+		Code:     "validate.error",
+		Severity: SeverityError,
+		Path:     Keys("line\nbreak"),
+		Message:  "message\r\nnext",
+		Primary:  &Location{SourceID: "source\tlabel", Line: 1},
+	}
+	var output bytes.Buffer
+	if err := WriteDiagnostics(&output, []Diagnostic{diagnostic}); err != nil {
+		t.Fatal(err)
+	}
+	got := output.String()
+	if strings.Count(got, "\n") != 1 {
+		t.Fatalf("control characters created output lines: %q", got)
+	}
+	for _, escaped := range []string{`line\nbreak`, `message\r\nnext`, `source\tlabel`} {
+		if !strings.Contains(got, escaped) {
+			t.Errorf("output %q does not contain %q", got, escaped)
+		}
+	}
+}
+
+func TestWriteDiagnosticsPropagatesWriterFailures(t *testing.T) {
+	t.Parallel()
+
+	diagnostics := []Diagnostic{{Severity: SeverityError, Message: "safe"}}
+	want := errors.New("write failed")
+	if err := WriteDiagnostics(errorWriter{err: want}, diagnostics); !errors.Is(err, want) {
+		t.Fatalf("error writer returned %v", err)
+	}
+	if err := WriteDiagnostics(shortWriter{}, diagnostics); !errors.Is(err, io.ErrShortWrite) {
+		t.Fatalf("short writer returned %v", err)
+	}
+}
+
+type errorWriter struct {
+	err error
+}
+
+func (w errorWriter) Write(p []byte) (int, error) {
+	return min(3, len(p)), w.err
+}
+
+type shortWriter struct{}
+
+func (shortWriter) Write(p []byte) (int, error) {
+	return max(0, len(p)-1), nil
+}

internal/engine/directives.go

@@ -0,0 +1,229 @@
+package engine
+
+import (
+	"path"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+const directiveKey = "configkit"
+
+type importDeclaration struct {
+	path     string
+	glob     string
+	optional bool
+	location Location
+}
+
+func splitImportDirectives(root *document.Node) (*document.Node, []importDeclaration, []Diagnostic) {
+	body := document.Clone(root)
+	var declarations []importDeclaration
+	directiveIndex := -1
+	for index, entry := range body.Mapping {
+		if entry.Key != directiveKey {
+			continue
+		}
+		directiveIndex = index
+		parsed, diagnostics := parseImportDirective(entry.Value, Keys(directiveKey))
+		if len(diagnostics) != 0 {
+			return nil, nil, diagnostics
+		}
+		declarations = parsed
+		break
+	}
+	if directiveIndex >= 0 {
+		body.Mapping = append(body.Mapping[:directiveIndex], body.Mapping[directiveIndex+1:]...)
+	}
+	if diagnostics := nestedDirectiveDiagnostics(body, Path{}); len(diagnostics) != 0 {
+		return nil, nil, diagnostics
+	}
+	return body, declarations, nil
+}
+
+func parseImportDirective(node *document.Node, directivePath Path) ([]importDeclaration, []Diagnostic) {
+	if node.Kind != document.Mapping {
+		return nil, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, directivePath, "configuration directive must be a mapping", node)}
+	}
+	var declarations []importDeclaration
+	for _, entry := range node.Mapping {
+		fieldPath := directivePath.Key(entry.Key)
+		if entry.Key != "imports" {
+			return nil, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, fieldPath, "configuration directive field is not recognized", entry.Value)}
+		}
+		if entry.Value.Kind != document.Sequence {
+			return nil, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, fieldPath, "imports must be a sequence", entry.Value)}
+		}
+		for index, item := range entry.Value.Sequence {
+			declaration, diagnostics := parseImportDeclaration(item, fieldPath.Index(index))
+			if len(diagnostics) != 0 {
+				return nil, diagnostics
+			}
+			declarations = append(declarations, declaration)
+		}
+	}
+	return declarations, nil
+}
+
+func parseImportDeclaration(node *document.Node, declarationPath Path) (importDeclaration, []Diagnostic) {
+	if node.Kind != document.Mapping {
+		return importDeclaration{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, declarationPath, "import declaration must be a mapping", node)}
+	}
+	declaration := importDeclaration{location: publicLocation(node.Location)}
+	seenTarget := false
+	for _, entry := range node.Mapping {
+		fieldPath := declarationPath.Key(entry.Key)
+		switch entry.Key {
+		case "path", "glob":
+			if seenTarget || entry.Value.Kind != document.String || entry.Value.Text == "" || strings.TrimSpace(entry.Value.Text) != entry.Value.Text {
+				return importDeclaration{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, fieldPath, "import declaration requires exactly one nonempty path or glob string", entry.Value)}
+			}
+			seenTarget = true
+			declaration.location = publicLocation(entry.Value.Location)
+			if entry.Key == "path" {
+				declaration.path = entry.Value.Text
+			} else {
+				declaration.glob = entry.Value.Text
+			}
+		case "optional":
+			if entry.Value.Kind != document.Boolean {
+				return importDeclaration{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, fieldPath, "optional must be a boolean", entry.Value)}
+			}
+			declaration.optional = entry.Value.Text == "true"
+		default:
+			return importDeclaration{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, fieldPath, "import declaration field is not recognized", entry.Value)}
+		}
+	}
+	if !seenTarget {
+		return importDeclaration{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, declarationPath, "import declaration requires exactly one path or glob", node)}
+	}
+	return declaration, nil
+}
+
+func nestedDirectiveDiagnostics(node *document.Node, current Path) []Diagnostic {
+	if node.Kind == document.Mapping {
+		for _, entry := range node.Mapping {
+			childPath := current.Key(entry.Key)
+			if entry.Key == directiveKey {
+				location := publicLocation(entry.KeyLocation)
+				return []Diagnostic{{Code: CodeImportInvalid, Severity: SeverityError, Path: childPath, Message: "configuration directives are permitted only at the document root", Primary: &location}}
+			}
+			if diagnostics := nestedDirectiveDiagnostics(entry.Value, childPath); len(diagnostics) != 0 {
+				return diagnostics
+			}
+		}
+	} else if node.Kind == document.Sequence {
+		for index, child := range node.Sequence {
+			if diagnostics := nestedDirectiveDiagnostics(child, current.Index(index)); len(diagnostics) != 0 {
+				return diagnostics
+			}
+		}
+	}
+	return nil
+}
+
+func fragmentVersionClaim(root *document.Node, rule *VersionRule) *document.Node {
+	if rule == nil {
+		return nil
+	}
+	current := root
+	if len(rule.Path.segments) == 0 {
+		return current
+	}
+	for _, segment := range rule.Path.segments {
+		if current.Kind != document.Mapping {
+			return current
+		}
+		if segment.kind == pathSegmentIndex {
+			return nil
+		}
+		key := segment.key
+		index := documentEntryIndex(current.Mapping, key)
+		if index < 0 {
+			return nil
+		}
+		current = current.Mapping[index].Value
+	}
+	return current
+}
+
+func validImportPath(value string) bool {
+	if value == "" || strings.TrimSpace(value) != value || path.IsAbs(value) || strings.HasPrefix(value, "//") {
+		return false
+	}
+	return !hasImportScheme(value)
+}
+
+func hasImportScheme(value string) bool {
+	colon := strings.IndexByte(value, ':')
+	slash := strings.IndexByte(value, '/')
+	if colon <= 0 || (slash >= 0 && slash < colon) {
+		return false
+	}
+	for index := 0; index < colon; index++ {
+		character := value[index]
+		if index == 0 {
+			if (character < 'a' || character > 'z') && (character < 'A' || character > 'Z') {
+				return false
+			}
+			continue
+		}
+		if (character < 'a' || character > 'z') && (character < 'A' || character > 'Z') &&
+			(character < '0' || character > '9') && character != '+' && character != '-' && character != '.' {
+			return false
+		}
+	}
+	return true
+}
+
+func nodeImportDiagnostic(code Code, path Path, message string, node *document.Node) Diagnostic {
+	location := publicLocation(node.Location)
+	return Diagnostic{Code: code, Severity: SeverityError, Path: path, Message: message, Primary: &location}
+}
+
+func overlayDirectiveDiagnostics(node *document.Node, current Path) []Diagnostic {
+	if node.Kind == document.Mapping {
+		for _, entry := range node.Mapping {
+			childPath := current.Key(entry.Key)
+			if entry.Key == directiveKey {
+				location := publicLocation(entry.KeyLocation)
+				return []Diagnostic{{
+					Code: CodeOverlayDirective, Severity: SeverityError, Path: childPath,
+					Message: "overlays cannot contain configuration directives", Primary: &location,
+				}}
+			}
+			if diagnostics := overlayDirectiveDiagnostics(entry.Value, childPath); len(diagnostics) != 0 {
+				return diagnostics
+			}
+		}
+	} else if node.Kind == document.Sequence {
+		for index, child := range node.Sequence {
+			if diagnostics := overlayDirectiveDiagnostics(child, current.Index(index)); len(diagnostics) != 0 {
+				return diagnostics
+			}
+		}
+	}
+	return nil
+}
+
+func disabledDirectiveDiagnostics(node *document.Node, path Path) []Diagnostic {
+	var diagnostics []Diagnostic
+	if node.Kind == document.Mapping {
+		for _, entry := range node.Mapping {
+			childPath := path.Key(entry.Key)
+			if entry.Key == directiveKey {
+				location := Location{SourceID: entry.KeyLocation.SourceID, Line: entry.KeyLocation.Line, Column: entry.KeyLocation.Column}
+				diagnostics = append(diagnostics, Diagnostic{
+					Code: CodeImportDisabled, Severity: SeverityError, Path: childPath,
+					Message: "configuration directives require imports to be enabled", Primary: &location,
+				})
+			}
+			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(entry.Value, childPath)...)
+		}
+	} else if node.Kind == document.Sequence {
+		for index, child := range node.Sequence {
+			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(child, path.Index(index))...)
+		}
+	}
+	return diagnostics
+}

internal/engine/document_compare.go

@@ -0,0 +1,110 @@
+package engine
+
+import (
+	"cmp"
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+	"slices"
+)
+
+type documentDeltaKind uint8
+
+const (
+	documentAdded documentDeltaKind = iota + 1
+	documentRemoved
+	documentReplaced
+)
+
+type documentDelta struct {
+	path Path
+	kind documentDeltaKind
+}
+
+// compareConfigurationValues ignores locations and sensitivity metadata. Mapping
+// order is immaterial; sequences are atomic for change reporting.
+func compareConfigurationValues(before, after *document.Node) []documentDelta {
+	var deltas []documentDelta
+	compareConfigurationValue(before, after, Path{}, &deltas)
+	slices.SortFunc(deltas, func(left, right documentDelta) int {
+		if order := cmp.Compare(left.path.String(), right.path.String()); order != 0 {
+			return order
+		}
+		return int(left.kind) - int(right.kind)
+	})
+	return deltas
+}
+
+func compareConfigurationValue(before, after *document.Node, path Path, deltas *[]documentDelta) {
+	if before == nil && after == nil {
+		return
+	}
+	if before == nil {
+		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentAdded})
+		return
+	}
+	if after == nil {
+		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentRemoved})
+		return
+	}
+	if before.Kind != after.Kind {
+		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
+		return
+	}
+	switch before.Kind {
+	case document.Mapping:
+		beforeEntries := make(map[string]*document.Node, len(before.Mapping))
+		afterEntries := make(map[string]*document.Node, len(after.Mapping))
+		keys := make(map[string]bool, len(before.Mapping)+len(after.Mapping))
+		for _, entry := range before.Mapping {
+			beforeEntries[entry.Key] = entry.Value
+			keys[entry.Key] = true
+		}
+		for _, entry := range after.Mapping {
+			afterEntries[entry.Key] = entry.Value
+			keys[entry.Key] = true
+		}
+		ordered := make([]string, 0, len(keys))
+		for key := range keys {
+			ordered = append(ordered, key)
+		}
+		slices.Sort(ordered)
+		for _, key := range ordered {
+			compareConfigurationValue(beforeEntries[key], afterEntries[key], path.Key(key), deltas)
+		}
+	case document.Sequence:
+		if !configurationValuesEqual(before, after) {
+			*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
+		}
+	default:
+		if before.Text != after.Text {
+			*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
+		}
+	}
+}
+
+// configurationValuesEqual compares only configuration values, not provenance or
+// sensitivity. Callers auditing validation must check sensitivity separately.
+func configurationValuesEqual(left, right *document.Node) bool {
+	if left == nil || right == nil {
+		return left == right
+	}
+	if left.Kind != right.Kind || left.Text != right.Text || len(left.Mapping) != len(right.Mapping) || len(left.Sequence) != len(right.Sequence) {
+		return false
+	}
+	if left.Kind == document.Mapping {
+		leftMap := make(map[string]*document.Node, len(left.Mapping))
+		for _, entry := range left.Mapping {
+			leftMap[entry.Key] = entry.Value
+		}
+		for _, entry := range right.Mapping {
+			if !configurationValuesEqual(leftMap[entry.Key], entry.Value) {
+				return false
+			}
+		}
+	}
+	for i := range left.Sequence {
+		if !configurationValuesEqual(left.Sequence[i], right.Sequence[i]) {
+			return false
+		}
+	}
+	return true
+}

internal/engine/document_walk.go

@@ -0,0 +1,86 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+// walkDocument visits value nodes in preorder, preserving stored mapping order
+// and sequence index order. Mapping keys are not separate nodes in this walk.
+// The callback borrows paths and nodes; clone any mutable state it retains.
+// Specialized origin, pruning, and budget traversals retain their own semantics.
+func walkDocument(node *document.Node, path Path, visit func(Path, *document.Node)) {
+	if node == nil {
+		return
+	}
+	visit(path, node)
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			walkDocument(entry.Value, path.Key(entry.Key), visit)
+		}
+	case document.Sequence:
+		for index, child := range node.Sequence {
+			walkDocument(child, path.Index(index), visit)
+		}
+	}
+}
+
+// indexDocument borrows nodes from its caller-owned tree.
+func indexDocument(node *document.Node, path Path, index map[string]*document.Node) {
+	walkDocument(node, path, func(path Path, node *document.Node) {
+		index[path.String()] = node
+	})
+}
+
+func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
+	if root == nil || !path.valid() {
+		return nil, false
+	}
+	current := root
+	for _, segment := range path.segments {
+		switch current.Kind {
+		case document.Mapping:
+			if segment.kind == pathSegmentIndex {
+				return nil, false
+			}
+			found := false
+			for _, entry := range current.Mapping {
+				if entry.Key == segment.key {
+					current = entry.Value
+					found = true
+					break
+				}
+			}
+			if !found {
+				return nil, false
+			}
+		case document.Sequence:
+			index, ok := schemaIndex(segment)
+			if !ok || index >= len(current.Sequence) {
+				return nil, false
+			}
+			current = current.Sequence[index]
+		default:
+			return nil, false
+		}
+	}
+	return current, true
+}
+
+// countInputNodes includes mapping-key nodes, unlike walkDocument's value-only
+// traversal. Aggregate source budgets charge every input occurrence.
+func countInputNodes(node *document.Node) int {
+	if node == nil {
+		return 0
+	}
+	count := 1
+	if node.Kind == document.Mapping {
+		count += len(node.Mapping)
+		for _, entry := range node.Mapping {
+			count += countInputNodes(entry.Value)
+		}
+	} else if node.Kind == document.Sequence {
+		for _, child := range node.Sequence {
+			count += countInputNodes(child)
+		}
+	}
+	return count
+}

internal/engine/explain.go

@@ -0,0 +1,122 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+// ValueSnapshot is a detached, deterministic YAML representation of one value.
+// Present distinguishes absence or deletion from an explicit null value.
+type ValueSnapshot struct {
+	Present  bool
+	Redacted bool
+	YAML     string
+}
+
+// ValueChange describes one explicit definition or audited domain operation.
+type ValueChange struct {
+	Before       ValueSnapshot
+	After        ValueSnapshot
+	Origin       Origin
+	Reasons      []string
+	Dependencies []Path
+}
+
+// SecretReferenceInfo describes a successfully resolved effective reference.
+// Name is the environment-variable name, never its value.
+type SecretReferenceInfo struct {
+	Name string
+}
+
+// Explanation is a detached safe account of one effective or historical path.
+type Explanation struct {
+	Path            Path
+	Effective       ValueSnapshot
+	Origin          Origin
+	History         []ValueChange
+	SecretReference *SecretReferenceInfo
+}
+
+// Explain returns safe effective and chronological values for a known final or
+// historical path. Unknown and malformed paths return false.
+func (r *Inspection) Explain(path Path) (Explanation, bool) {
+	if r == nil || r.final == nil || r.baseline == nil || !r.metadata.hasHistoricalPath(path) {
+		return Explanation{}, false
+	}
+	explanation := Explanation{Path: path.clone(), Effective: valueSnapshot(r.final, path, r.secrets)}
+	if info, ok := r.metadata.Lookup(path); ok {
+		explanation.Origin = cloneOrigin(info.Origin)
+	}
+
+	working := document.Clone(r.baseline)
+	if _, present := documentAtPath(working, path); present {
+		explanation.History = append(explanation.History, ValueChange{
+			After: valueSnapshot(working, path, r.secrets), Origin: Origin{Layer: LayerDefault},
+		})
+	}
+	for _, application := range r.applications {
+		operationPath, relevant := applicationOperationPath(application, path)
+		var before ValueSnapshot
+		if relevant {
+			before = valueSnapshot(working, path, r.secrets)
+		}
+		applyHistoryApplication(&working, application)
+		if !relevant {
+			continue
+		}
+		after := valueSnapshot(working, path, r.secrets)
+		if !before.Present && !after.Present {
+			continue
+		}
+		explanation.History = append(explanation.History, ValueChange{
+			Before: before,
+			After:  after,
+			Origin: historyApplicationOrigin(application, operationPath),
+		})
+	}
+
+	// Intermediate input replacements do not permanently suppress defaults:
+	// decoding applies them to the final input tree. Show that reconciliation
+	// explicitly, including canonical scalar conversions, before domain changes.
+	replayed, _ := documentAtPath(working, path)
+	decoded, _ := documentAtPath(r.input, path)
+	if !configurationValuesEqual(replayed, decoded) {
+		origin := cloneOrigin(r.inputOrigins[path.String()])
+		origin.Operation = ChangeDecoding
+		explanation.History = append(explanation.History, ValueChange{
+			Before:  valueSnapshot(working, path, r.secrets),
+			After:   valueSnapshot(r.input, path, r.secrets),
+			Origin:  origin,
+			Reasons: []string{"applied retained defaults and canonical typed decoding"},
+		})
+	}
+
+	working = document.Clone(r.input)
+	for _, snapshot := range coalescedResolutionSnapshots(r.resolution) {
+		relevant := pathsIntersect(snapshot.change.Path, path)
+		var before ValueSnapshot
+		if relevant {
+			before = valueSnapshot(working, path, r.secrets)
+		}
+		replaceHistoryPath(&working, snapshot.change.Path, snapshot.after)
+		if !relevant {
+			continue
+		}
+		after := valueSnapshot(working, path, r.secrets)
+		if !before.Present && !after.Present {
+			continue
+		}
+		explanation.History = append(explanation.History, ValueChange{
+			Before:       before,
+			After:        after,
+			Origin:       cloneOrigin(snapshot.change.Origin),
+			Reasons:      append([]string(nil), snapshot.change.Reasons...),
+			Dependencies: clonePaths(snapshot.change.Dependencies),
+		})
+	}
+
+	if !explanation.Effective.Present && len(explanation.History) == 0 {
+		return Explanation{}, false
+	}
+	if name, ok := r.secretReferences[path.String()]; ok && !pathIsSecret(r.secrets, path) {
+		explanation.SecretReference = &SecretReferenceInfo{Name: name}
+	}
+	return explanation, true
+}

internal/engine/explain_render.go

@@ -0,0 +1,123 @@
+package engine
+
+import (
+	"errors"
+	"io"
+	"strconv"
+	"strings"
+)
+
+var (
+	errExplanationUnavailable = errors.New("configkit: configuration explanation is unavailable")
+	errExplanationUnknownPath = errors.New("configkit: configuration explanation path is unknown")
+)
+
+// WriteExplanation writes a deterministic human-readable rendering of Explain.
+// Unknown paths produce no output. Writer failures may leave partial output.
+func (r *Inspection) WriteExplanation(output io.Writer, path Path) error {
+	if r == nil || output == nil {
+		return errExplanationUnavailable
+	}
+	explanation, ok := r.Explain(path)
+	if !ok {
+		return errExplanationUnknownPath
+	}
+	var rendered strings.Builder
+	rendered.WriteString("path: ")
+	rendered.WriteString(strconv.Quote(explanation.Path.String()))
+	rendered.WriteByte('\n')
+	writeExplanationOrigin(&rendered, "effective source", explanation.Origin, r.sources)
+	writeExplanationSnapshot(&rendered, "effective (canonical typed)", explanation.Effective, 0)
+	if explanation.SecretReference != nil {
+		rendered.WriteString("secret reference: ")
+		rendered.WriteString(strconv.Quote(explanation.SecretReference.Name))
+		rendered.WriteString(" (resolved from process environment)\n")
+	}
+	rendered.WriteString("history:\n")
+	for _, change := range explanation.History {
+		rendered.WriteString("  - representation: ")
+		if change.Origin.Operation == ChangeDecoding {
+			rendered.WriteString("input to canonical typed\n")
+		} else if change.Origin.Layer == LayerBase || change.Origin.Layer == LayerOverlay || change.Origin.Layer == LayerCLI {
+			rendered.WriteString("policy-validated input\n")
+		} else {
+			rendered.WriteString("canonical typed\n")
+		}
+		writeExplanationOrigin(&rendered, "    source", change.Origin, r.sources)
+		writeExplanationSnapshot(&rendered, "    before", change.Before, 4)
+		writeExplanationSnapshot(&rendered, "    after", change.After, 4)
+		for _, reason := range change.Reasons {
+			rendered.WriteString("    reason: ")
+			rendered.WriteString(strconv.Quote(reason))
+			rendered.WriteByte('\n')
+		}
+		for _, dependency := range change.Dependencies {
+			rendered.WriteString("    dependency: ")
+			rendered.WriteString(strconv.Quote(dependency.String()))
+			rendered.WriteByte('\n')
+		}
+	}
+	data := []byte(rendered.String())
+	written, err := output.Write(data)
+	if err == nil && written != len(data) {
+		return io.ErrShortWrite
+	}
+	return err
+}
+
+func writeExplanationOrigin(output *strings.Builder, label string, origin Origin, sources []SourceInfo) {
+	output.WriteString(label)
+	output.WriteString(": layer=")
+	output.WriteString(strconv.Quote(string(origin.Layer)))
+	if origin.Operation != "" {
+		output.WriteString(" operation=")
+		output.WriteString(strconv.Quote(string(origin.Operation)))
+	}
+	output.WriteByte('\n')
+	for _, location := range origin.Locations {
+		output.WriteString("      location: source=")
+		output.WriteString(strconv.Quote(location.SourceID))
+		if label := sourceLabel(sources, location.SourceID); label != "" {
+			output.WriteString(" label=")
+			output.WriteString(strconv.Quote(label))
+		}
+		output.WriteString(" line=")
+		output.WriteString(strconv.Itoa(location.Line))
+		output.WriteString(" column=")
+		output.WriteString(strconv.Itoa(location.Column))
+		output.WriteByte('\n')
+	}
+}
+
+func sourceLabel(sources []SourceInfo, sourceID string) string {
+	for _, source := range sources {
+		if source.ID == sourceID {
+			return source.Label
+		}
+	}
+	return ""
+}
+
+func writeExplanationSnapshot(output *strings.Builder, label string, snapshot ValueSnapshot, indent int) {
+	if !snapshot.Present {
+		output.WriteString(label)
+		output.WriteString(": absent\n")
+		return
+	}
+	output.WriteString(label)
+	if snapshot.Redacted {
+		output.WriteString(" (redacted)")
+	}
+	output.WriteString(":\n")
+	prefix := strings.Repeat(" ", indent+2)
+	for _, line := range strings.SplitAfter(snapshot.YAML, "\n") {
+		if line == "" {
+			continue
+		}
+		output.WriteString(prefix)
+		output.WriteString(line)
+		if !strings.HasSuffix(line, "\n") {
+			output.WriteByte('\n')
+		}
+	}
+}

internal/engine/explain_test.go

@@ -0,0 +1,522 @@
+package engine
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type explanationConcurrency struct {
+	Transcription struct {
+		Concurrency int `yaml:"concurrency"`
+	} `yaml:"transcription"`
+}
+
+func TestExplainShowsDefaultBaseAndEffectiveOverlayValue(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "config.yml", "configkit:\n  imports: [{path: transcription.yml}]\n")
+	writeImportFile(t, directory, "transcription.yml", "transcription:\n  concurrency: 8\n")
+	writeImportFile(t, directory, filepath.Join("overlays", "testing.yml"), "transcription:\n  concurrency: 1\n")
+	result, err := testLoad[explanationConcurrency](File(mainPath), Options[explanationConcurrency]{
+		Imports: true, Overlay: "testing",
+		Definition: Definition[explanationConcurrency]{Defaults: func() explanationConcurrency {
+			value := explanationConcurrency{}
+			value.Transcription.Concurrency = 4
+			return value
+		}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	explanation, ok := result.Explain(Keys("transcription", "concurrency"))
+	if !ok {
+		t.Fatal("known path was not explained")
+	}
+	if got := explanationValues(explanation); !reflect.DeepEqual(got, []string{"4\n", "8\n", "1\n"}) {
+		t.Fatalf("history values = %#v", got)
+	}
+	if explanation.Effective.YAML != "1\n" || explanation.Origin.Layer != LayerOverlay ||
+		len(explanation.Origin.Locations) != 1 || explanation.Origin.Locations[0].SourceID != "source-3" ||
+		explanation.Origin.Locations[0].Line != 2 {
+		t.Fatalf("effective explanation = %#v", explanation)
+	}
+	var rendered bytes.Buffer
+	if err := result.WriteExplanation(&rendered, Keys("transcription", "concurrency")); err != nil ||
+		!strings.Contains(rendered.String(), `layer="overlay"`) ||
+		!strings.Contains(rendered.String(), `label="overlays/testing.yml"`) {
+		t.Fatalf("rendered explanation = %v\n%s", err, rendered.String())
+	}
+}
+
+type explanationConfig struct {
+	Concurrency int               `yaml:"concurrency"`
+	Equal       string            `yaml:"equal"`
+	Limit       int               `yaml:"limit"`
+	Items       []string          `yaml:"items"`
+	Labels      map[string]string `yaml:"labels"`
+	Dynamic     any               `yaml:"dynamic"`
+	Maybe       *string           `yaml:"maybe"`
+	Empty       []string          `yaml:"empty"`
+	Credential  Secret            `yaml:"credential"`
+	Classified  Secret            `yaml:"classified"`
+	DerivedA    string            `yaml:"derived_a"`
+	DerivedB    string            `yaml:"derived_b"`
+}
+
+func TestExplainReplaysCLIResolutionContainersAndSafeHistoricalValues(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "config.yml", `concurrency: 8
+equal: same
+limit: wrong-before-overlay
+items: [base, removed]
+labels: {base: retained}
+dynamic: {retired: HISTORICAL_EXPLAIN_CANARY, public: visible}
+credential: APP_SECRET
+classified: APP_SECRET
+`)
+	writeImportFile(t, directory, filepath.Join("overlays", "testing.yml"), `concurrency: 1
+equal: same
+limit: 7
+items: [overlay]
+labels: {overlay: retained}
+dynamic: selected
+`)
+	result, err := testLoadWithSecretLookup(File(mainPath), func(name string) (string, bool) {
+		if name != "APP_SECRET" {
+			t.Fatalf("secret lookup = %q", name)
+		}
+		return "RESOLVED_EXPLAIN_CANARY", true
+	}, Options[explanationConfig]{
+		Overlay: "testing",
+		Overrides: []Override{
+			{Path: Keys("concurrency"), Value: 2, Flag: "--concurrency"},
+			{Path: Keys("equal"), Value: "same", Flag: "--equal"},
+			{Path: Keys("items"), Value: []any{"cli", "restored"}, Flag: "--items"},
+			{Path: Keys("labels"), Value: map[string]any{"cli": "retained"}, Flag: "--label"},
+		},
+		Definition: Definition[explanationConfig]{
+			Defaults: func() explanationConfig {
+				return explanationConfig{
+					Concurrency: 4, Equal: "same", Labels: map[string]string{"default": "retained"},
+					Maybe: nil, Empty: []string{}, Credential: SecretEnv("APP_SECRET"), Classified: SecretEnv("APP_SECRET"),
+				}
+			},
+			Secret: func(path Path) bool {
+				return path.String() == "/dynamic/retired" || path.String() == "/classified"
+			},
+			Resolve: func(configuration *explanationConfig, resolution *Resolution) error {
+				Normalize(resolution, Keys("concurrency"), &configuration.Concurrency, 3,
+					"normalized\nconcurrency", Keys("labels"))
+				Normalize(resolution, Keys("equal"), &configuration.Equal, "same", "record equal value")
+				Normalize(resolution, Keys("derived_a"), &configuration.DerivedA, "DERIVED_EXPLAIN_A",
+					"derived cycle a", Keys("derived_b"))
+				Normalize(resolution, Keys("derived_b"), &configuration.DerivedB, "DERIVED_EXPLAIN_B",
+					"derived cycle b", Keys("derived_a"), Keys("dynamic"))
+				return nil
+			},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	concurrency, ok := result.Explain(Keys("concurrency"))
+	if !ok {
+		t.Fatal("concurrency was not explained")
+	}
+	if got := explanationValues(concurrency); !reflect.DeepEqual(got, []string{"4\n", "8\n", "1\n", "2\n", "3\n"}) {
+		t.Fatalf("concurrency history = %#v", got)
+	}
+	if got := historyValueLayers(concurrency); !reflect.DeepEqual(got, []Layer{LayerDefault, LayerBase, LayerOverlay, LayerCLI, LayerResolution}) {
+		t.Fatalf("concurrency layers = %#v", got)
+	}
+	if concurrency.History[4].Before.YAML != "2\n" || concurrency.History[4].Reasons[0] != "normalized\nconcurrency" ||
+		concurrency.History[4].Dependencies[0].String() != "/labels" {
+		t.Fatalf("resolution history = %#v", concurrency.History[4])
+	}
+
+	equal, _ := result.Explain(Keys("equal"))
+	if len(equal.History) != 5 {
+		t.Fatalf("equal writes were lost: %#v", equal.History)
+	}
+	for _, change := range equal.History[1:] {
+		if change.Before.YAML != "same\n" || change.After.YAML != "same\n" {
+			t.Fatalf("equal replacement = %#v", change)
+		}
+	}
+
+	limit, _ := result.Explain(Keys("limit"))
+	if got := explanationValues(limit); !reflect.DeepEqual(got, []string{"0\n", "wrong-before-overlay\n", "7\n"}) {
+		t.Fatalf("overridden invalid input was not retained: %#v", got)
+	}
+	removed, ok := result.Explain(Keys("dynamic", "retired"))
+	if !ok || removed.Effective.Present || len(removed.History) < 2 {
+		t.Fatalf("removed path = %#v, %v", removed, ok)
+	}
+	for _, change := range removed.History {
+		if strings.Contains(change.Before.YAML+change.After.YAML, "HISTORICAL_EXPLAIN_CANARY") {
+			t.Fatalf("historical secret escaped redaction: %#v", change)
+		}
+	}
+	if !removed.History[0].After.Redacted || removed.History[len(removed.History)-1].After.Present {
+		t.Fatalf("removed secret history = %#v", removed.History)
+	}
+	dynamic, _ := result.Explain(Keys("dynamic"))
+	if len(dynamic.History) < 3 || !dynamic.History[1].After.Redacted ||
+		strings.Contains(dynamic.History[1].After.YAML, "HISTORICAL_EXPLAIN_CANARY") {
+		t.Fatalf("container redaction history = %#v", dynamic.History)
+	}
+
+	items, _ := result.Explain(Keys("items"))
+	if len(items.History) != 4 || !strings.Contains(items.History[1].After.YAML, "removed") ||
+		strings.Contains(items.History[2].After.YAML, "removed") || !strings.Contains(items.History[3].After.YAML, "restored") {
+		t.Fatalf("atomic sequence history = %#v", items.History)
+	}
+	removedIndex, ok := result.Explain(Keys("items").Index(1))
+	if !ok || !removedIndex.History[1].Before.Present || removedIndex.History[1].After.Present ||
+		!removedIndex.History[2].After.Present {
+		t.Fatalf("sequence descendant history = %#v", removedIndex.History)
+	}
+	labels, _ := result.Explain(Keys("labels"))
+	if len(labels.History) != 4 || !strings.Contains(labels.Effective.YAML, "default: retained") ||
+		!strings.Contains(labels.Effective.YAML, "overlay: retained") || !strings.Contains(labels.Effective.YAML, "cli: retained") {
+		t.Fatalf("composite mapping history = %#v", labels)
+	}
+	if labels.Origin.Layer != LayerCLI || len(labels.Origin.Locations) != 3 {
+		t.Fatalf("composite effective origin = %#v", labels.Origin)
+	}
+
+	maybe, _ := result.Explain(Keys("maybe"))
+	empty, _ := result.Explain(Keys("empty"))
+	if !maybe.Effective.Present || maybe.Effective.YAML != "null\n" || !empty.Effective.Present || empty.Effective.YAML != "[]\n" {
+		t.Fatalf("null/empty snapshots = maybe %#v empty %#v", maybe.Effective, empty.Effective)
+	}
+	credential, _ := result.Explain(Keys("credential"))
+	if credential.SecretReference == nil || credential.SecretReference.Name != "APP_SECRET" || credential.Effective.YAML != "APP_SECRET\n" {
+		t.Fatalf("secret reference = %#v", credential)
+	}
+	classified, _ := result.Explain(Keys("classified"))
+	if classified.SecretReference != nil || !classified.Effective.Redacted ||
+		strings.Contains(classified.Effective.YAML, "APP_SECRET") {
+		t.Fatalf("classified secret reference = %#v", classified)
+	}
+	var derivedExplanations []Explanation
+	for _, path := range []Path{Keys("derived_a"), Keys("derived_b")} {
+		derived, _ := result.Explain(path)
+		if !derived.Effective.Redacted || strings.Contains(derived.Effective.YAML, "DERIVED_EXPLAIN") {
+			t.Fatalf("dependency closure at %s = %#v", path.String(), derived)
+		}
+		derivedExplanations = append(derivedExplanations, derived)
+	}
+
+	formatted := fmt.Sprintf("%v %#v %v", removed, credential, derivedExplanations)
+	encoded, marshalErr := json.Marshal(append([]Explanation{removed, credential, classified}, derivedExplanations...))
+	if marshalErr != nil || strings.Contains(formatted+string(encoded), "RESOLVED_EXPLAIN_CANARY") ||
+		strings.Contains(formatted+string(encoded), "HISTORICAL_EXPLAIN_CANARY") ||
+		strings.Contains(formatted+string(encoded), "DERIVED_EXPLAIN") {
+		t.Fatalf("public records disclosed a canary: %s %s", formatted, encoded)
+	}
+
+	concurrency.Path.segments[0].key = "mutated"
+	concurrency.History[4].Reasons[0] = "mutated"
+	concurrency.History[4].Dependencies[0].segments[0].key = "mutated"
+	result.Config.Concurrency = 99
+	again, _ := result.Explain(Keys("concurrency"))
+	if again.Path.String() != "/concurrency" || again.Effective.YAML != "3\n" ||
+		again.History[4].Reasons[0] != "normalized\nconcurrency" ||
+		again.History[4].Dependencies[0].String() != "/labels" {
+		t.Fatalf("returned explanation aliased internal history: %#v", again)
+	}
+
+	var first, second bytes.Buffer
+	if err := result.WriteExplanation(&first, Keys("concurrency")); err != nil {
+		t.Fatal(err)
+	}
+	if err := result.WriteExplanation(&second, Keys("concurrency")); err != nil || first.String() != second.String() {
+		t.Fatalf("nondeterministic rendering: %v\n%s\n%s", err, first.String(), second.String())
+	}
+	if strings.Contains(first.String(), "\nconcurrency\"") || !strings.Contains(first.String(), `"normalized\nconcurrency"`) {
+		t.Fatalf("reason controls were not escaped: %q", first.String())
+	}
+	unknownOutput := bytes.NewBufferString("unchanged")
+	if err := result.WriteExplanation(unknownOutput, Keys("unknown")); !errors.Is(err, errExplanationUnknownPath) || unknownOutput.String() != "unchanged" {
+		t.Fatalf("unknown writer = %q, %v", unknownOutput.String(), err)
+	}
+	if _, ok := result.Explain(Keys("items").Index(-1)); ok {
+		t.Fatal("malformed path was explained")
+	}
+	wantWriteError := errors.New("write failed")
+	if err := result.WriteExplanation(errorWriter{err: wantWriteError}, Keys("concurrency")); !errors.Is(err, wantWriteError) {
+		t.Fatalf("writer error = %v", err)
+	}
+	if err := result.WriteExplanation(shortWriter{}, Keys("concurrency")); !errors.Is(err, io.ErrShortWrite) {
+		t.Fatalf("short writer error = %v", err)
+	}
+	var invalidInput bytes.Buffer
+	if err := result.WriteExplanation(&invalidInput, Keys("limit")); err != nil ||
+		!strings.Contains(invalidInput.String(), "policy-validated input") ||
+		strings.Contains(invalidInput.String(), "wrong-before-overlay\n    source: layer=\"base\"\n    before (canonical typed)") {
+		t.Fatalf("historical representation rendering = %v\n%s", err, invalidInput.String())
+	}
+}
+
+func TestSecretsBootstrapLoadAndExplanationRemainSeparateAndSafe(t *testing.T) {
+	const name = "CONFIGKIT_EXPLAIN_BOOTSTRAP_TEST"
+	previous, present := os.LookupEnv(name)
+	if err := os.Unsetenv(name); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if present {
+			_ = os.Setenv(name, previous)
+		} else {
+			_ = os.Unsetenv(name)
+		}
+	})
+	directory := t.TempDir()
+	writeSecretTestFile(t, directory, name, "BOOTSTRAP_EXPLAIN_CANARY\n")
+	report, err := LoadSecretsDir(directory)
+	if err != nil || len(report.Entries()) != 1 || report.Entries()[0].Status != SecretFileLoaded {
+		t.Fatalf("bootstrap = %#v, %v", report, err)
+	}
+	type config struct {
+		Credential Secret `yaml:"credential"`
+	}
+	result, err := testLoad[config](Bytes("config.yml", []byte("credential: "+name+"\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var output bytes.Buffer
+	if err := result.WriteExplanation(&output, Keys("credential")); err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(output.String(), name) || strings.Contains(output.String(), "BOOTSTRAP_EXPLAIN_CANARY") {
+		t.Fatalf("explanation mixed bootstrap value into reference report: %s", output.String())
+	}
+}
+
+func TestHistoryNodeBudgetCountsSharedTreesOnce(t *testing.T) {
+	leaf := &document.Node{Kind: document.String, Text: "value"}
+	root := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{Key: "value", Value: leaf}}}
+	applications := []historyApplication{{layer: LayerBase, value: root}}
+	if !historyNodesWithin(2, root, root, root, applications, nil) {
+		t.Fatal("structurally shared history was counted more than once")
+	}
+	other := document.Clone(root)
+	if historyNodesWithin(3, root, other, root, applications, nil) {
+		t.Fatal("distinct retained nodes did not consume the budget")
+	}
+}
+
+func explanationValues(explanation Explanation) []string {
+	values := make([]string, len(explanation.History))
+	for index, change := range explanation.History {
+		values[index] = change.After.YAML
+	}
+	return values
+}
+
+func historyValueLayers(explanation Explanation) []Layer {
+	layers := make([]Layer, len(explanation.History))
+	for index, change := range explanation.History {
+		layers[index] = change.Origin.Layer
+	}
+	return layers
+}
+
+func TestExplanationReconcilesDefaultsAfterInputReplacement(t *testing.T) {
+	type cfg struct {
+		M map[string]int `yaml:"m"`
+	}
+	for _, base := range []string{"null", "replaced-text"} {
+		for _, cli := range []bool{false, true} {
+			t.Run(fmt.Sprintf("%s/cli=%v", base, cli), func(t *testing.T) {
+				root := t.TempDir()
+				main := writeImportFile(t, root, "main.yml", "m: "+base+"\n")
+				opts := Options[cfg]{Definition: Definition[cfg]{Defaults: func() cfg { return cfg{M: map[string]int{"a": 1}} }}}
+				if cli {
+					opts.Overrides = []Override{{Path: Keys("m"), Value: map[string]any{"b": 2}, Flag: "--m"}}
+				} else {
+					writeImportFile(t, root, "overlays/p.yml", "m: {b: 2}\n")
+					opts.Overlay = "p"
+				}
+				result, err := testLoad(File(main), opts)
+				if err != nil {
+					t.Fatal(err)
+				}
+				for _, path := range []Path{Keys("m"), Keys("m", "a")} {
+					explanation, ok := result.Explain(path)
+					if !ok {
+						t.Fatal("missing explanation")
+					}
+					last := explanation.History[len(explanation.History)-1]
+					if last.After != explanation.Effective || last.Origin.Operation != ChangeDecoding {
+						t.Fatalf("history does not reconcile final value: %#v", explanation)
+					}
+					info, _ := result.Metadata().Lookup(path)
+					if last.Origin.Layer != info.Origin.Layer {
+						t.Fatal("decoding lost effective origin")
+					}
+				}
+			})
+		}
+	}
+}
+
+func TestIntegerVersionInspectionRetainsInputAndReconcilesTypedValue(t *testing.T) {
+	type config struct {
+		Version string `yaml:"version"`
+	}
+	rule := &VersionRule{Path: Keys("version"), Check: func(version Version, _ *Validation) error {
+		if version.Text != "4" {
+			t.Errorf("version = %#v", version)
+		}
+		return nil
+	}}
+	options := Options[config]{Definition: Definition[config]{
+		Defaults: func() config { return config{Version: "4"} },
+		Version:  rule,
+	}}
+	first, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if first.Config.Version != "4" || second.Config.Version != "4" {
+		t.Fatalf("configurations = %#v / %#v", first.Config, second.Config)
+	}
+	inputVersion, inputOK := documentAtPath(first.applications[0].value, Keys("version"))
+	finalVersion, finalOK := documentAtPath(first.final, Keys("version"))
+	if !inputOK || inputVersion.Kind != document.Number || inputVersion.Text != "4" ||
+		!finalOK || finalVersion.Kind != document.String || finalVersion.Text != "4" {
+		t.Fatalf("input/final = %#v / %#v", inputVersion, finalVersion)
+	}
+
+	info, ok := first.Metadata().Lookup(Keys("version"))
+	if !ok || !info.Explicit || info.Null || info.Origin.Layer != LayerBase || len(info.Origin.Locations) != 1 ||
+		info.Origin.Locations[0].SourceID != "source-1" || info.Origin.Locations[0].Line != 1 {
+		t.Fatalf("version metadata = %#v, %v", info, ok)
+	}
+	explanation, ok := first.Explain(Keys("version"))
+	if !ok || explanation.Effective.YAML != "'4'\n" {
+		t.Fatalf("version explanation = %#v, %v", explanation, ok)
+	}
+	foundInput, foundDecoding := false, false
+	for _, change := range explanation.History {
+		if change.After.YAML == "4\n" && change.Origin.Layer == LayerBase {
+			foundInput = true
+		}
+		if change.Before.YAML == "4\n" && change.After.YAML == "'4'\n" && change.Origin.Operation == ChangeDecoding {
+			foundDecoding = true
+		}
+		if change.Origin.Layer == LayerResolution {
+			t.Fatalf("conversion recorded as resolution: %#v", change)
+		}
+	}
+	if !foundInput || !foundDecoding {
+		t.Fatalf("version history = %#v", explanation.History)
+	}
+	paths := first.Metadata().HistoricalPaths()
+	foundPath := false
+	for _, path := range paths {
+		if path.String() == "/version" {
+			foundPath = true
+		}
+	}
+	if !foundPath || len(first.Metadata().History(Keys("version"))) < 2 {
+		t.Fatalf("historical version paths/history = %#v / %#v", paths, first.Metadata().History(Keys("version")))
+	}
+
+	var effective strings.Builder
+	if err := first.WriteEffective(&effective); err != nil || effective.String() != "version: '4'\n" {
+		t.Fatalf("effective output = %q, %v", effective.String(), err)
+	}
+	first.Config.Version = "mutated"
+	effective.Reset()
+	if err := first.WriteEffective(&effective); err != nil || effective.String() != "version: '4'\n" || second.Config.Version != "4" {
+		t.Fatalf("detached results = %q / %#v, %v", effective.String(), second.Config, err)
+	}
+}
+
+func TestSensitiveIntegerVersionStaysRedactedWithoutSecretLookup(t *testing.T) {
+	type config struct {
+		Version string `yaml:"version"`
+	}
+	lookups := 0
+	result, err := testLoadWithSecretLookup(Bytes("version.yml", []byte("version: 987654321\n")), func(string) (string, bool) {
+		lookups++
+		return "CREDENTIAL_CANARY", true
+	}, Options[config]{Definition: Definition[config]{
+		Version: &VersionRule{Path: Keys("version"), Check: func(Version, *Validation) error { return nil }},
+		Secret:  func(path Path) bool { return path.String() == "/version" },
+	}})
+	if err != nil || result.Config.Version != "987654321" || lookups != 0 {
+		t.Fatalf("result = %#v, lookups = %d, err = %v", result, lookups, err)
+	}
+	var effective strings.Builder
+	if err := result.WriteEffective(&effective); err != nil {
+		t.Fatal(err)
+	}
+	explanation, ok := result.Explain(Keys("version"))
+	formatted := effective.String() + fmt.Sprintf("%#v %#v", explanation, result.Metadata().History(Keys("version")))
+	if !ok || !explanation.Effective.Redacted || strings.Contains(formatted, "987654321") || strings.Contains(formatted, "CREDENTIAL_CANARY") {
+		t.Fatalf("sensitive inspection = %q / %#v", effective.String(), explanation)
+	}
+}
+
+func TestExplanationReplaysResolutionAdditionsAndOverlappingIntent(t *testing.T) {
+	type cfg struct {
+		M map[string]any `yaml:"m"`
+	}
+	for _, overlap := range []bool{false, true} {
+		t.Run(fmt.Sprint(overlap), func(t *testing.T) {
+			result, err := testLoad(Bytes("base", []byte("m: {old: 1}\n")), Options[cfg]{Definition: Definition[cfg]{Resolve: func(c *cfg, r *Resolution) error {
+				c.M["new"] = map[string]any{"child": int64(7)}
+				delete(c.M, "old")
+				r.Record(Keys("m", "new"), ChangeDerivedDefault, "add nested", Keys("m", "old"))
+				r.Record(Keys("m", "old"), ChangeNormalization, "remove old")
+				if overlap {
+					r.Record(Keys("m"), ChangeNormalization, "update container")
+				}
+				return nil
+			}}})
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, path := range []Path{Keys("m"), Keys("m", "new"), Keys("m", "new", "child"), Keys("m", "old")} {
+				x, ok := result.Explain(path)
+				if !ok {
+					t.Fatal("missing known history")
+				}
+				var count int
+				for _, v := range x.History {
+					if v.Origin.Layer == LayerResolution {
+						count++
+						if overlap && len(v.Reasons) != 3 {
+							t.Fatal("lost overlapping intent")
+						}
+					}
+				}
+				if overlap && count != 1 {
+					t.Fatalf("overlapping records applied %d times", count)
+				}
+				last := x.History[len(x.History)-1]
+				if last.After != x.Effective {
+					t.Fatalf("incorrect replay for %s: %#v", path, x)
+				}
+			}
+		})
+	}
+}

internal/engine/filesystem.go

@@ -0,0 +1,121 @@
+package engine
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func validateFilesystemContext(source Source, context *FilesystemContext, main parsedSource) *Diagnostic {
+	rootPath, _, _, diagnostic := importFilesystem(source, context, main)
+	if diagnostic != nil {
+		return diagnostic
+	}
+	root, err := os.OpenRoot(rootPath)
+	if err != nil {
+		value := globFilesystemDiagnostic(err, "configuration root could not be opened", Location{})
+		value.Primary = nil
+		return &value
+	}
+	if err := root.Close(); err != nil {
+		value := importDiagnostic(CodeImportRead, "configuration root could not be closed", nil)
+		return &value
+	}
+	return nil
+}
+
+func filesystemOptionDiagnostics(source Source, context *FilesystemContext) []Diagnostic {
+	switch source.kind {
+	case sourceNone:
+		return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "NoSource cannot use filesystem context")}
+	case sourceFile:
+		if context.BaseDir != "" {
+			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")}
+		}
+	case sourceBytes, sourceReader:
+		if context.BaseDir == "" || context.Root == "" {
+			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "byte and reader filesystem context requires base and root directories")}
+		}
+		if !filepath.IsAbs(context.BaseDir) || !filepath.IsAbs(context.Root) {
+			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "byte and reader filesystem base and root directories must be absolute")}
+		}
+	}
+	return nil
+}
+
+func importFilesystem(source Source, context *FilesystemContext, main parsedSource) (rootPath, basePath, mainPath string, diagnostic *Diagnostic) {
+	if main.source == nil || main.document == nil {
+		value := importDiagnostic(CodeImportInvalid, "imports require a selected configuration source", nil)
+		return "", "", "", &value
+	}
+
+	if source.kind == sourceFile {
+		if context != nil && context.BaseDir != "" {
+			value := optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")
+			return "", "", "", &value
+		}
+		canonical, err := canonicalExistingPath(source.path)
+		if err != nil {
+			value := importDiagnostic(CodeImportInvalid, "selected source path could not be canonicalized", nil)
+			return "", "", "", &value
+		}
+		mainPath = canonical
+		basePath = filepath.Dir(canonical)
+		rootPath = basePath
+		if context != nil && context.Root != "" {
+			rootPath, err = canonicalExistingPath(context.Root)
+			if err != nil {
+				value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
+				return "", "", "", &value
+			}
+		}
+	} else {
+		if context == nil || context.BaseDir == "" || context.Root == "" {
+			value := optionDiagnostic(CodeOptionsInvalid, "byte and reader imports require absolute base and root directories")
+			return "", "", "", &value
+		}
+		if !filepath.IsAbs(context.BaseDir) || !filepath.IsAbs(context.Root) {
+			value := optionDiagnostic(CodeOptionsInvalid, "byte and reader import base and root directories must be absolute")
+			return "", "", "", &value
+		}
+		var err error
+		basePath, err = canonicalExistingPath(context.BaseDir)
+		if err != nil {
+			value := importDiagnostic(CodeImportInvalid, "import base directory could not be canonicalized", nil)
+			return "", "", "", &value
+		}
+		rootPath, err = canonicalExistingPath(context.Root)
+		if err != nil {
+			value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
+			return "", "", "", &value
+		}
+	}
+	if !containedPath(rootPath, basePath) || (mainPath != "" && !containedPath(rootPath, mainPath)) {
+		value := importDiagnostic(CodeImportOutsideRoot, "selected source and import base must stay inside the configuration root", nil)
+		return "", "", "", &value
+	}
+	for _, candidate := range []string{rootPath, basePath} {
+		info, err := os.Stat(candidate)
+		if err != nil || !info.IsDir() {
+			value := importDiagnostic(CodeImportInvalid, "configuration root and import base must be directories", nil)
+			return "", "", "", &value
+		}
+	}
+	return rootPath, basePath, mainPath, nil
+}
+
+func canonicalExistingPath(name string) (string, error) {
+	absolute, err := filepath.Abs(name)
+	if err != nil {
+		return "", err
+	}
+	return filepath.EvalSymlinks(filepath.Clean(absolute))
+}
+
+func containedPath(root, target string) bool {
+	relative, err := filepath.Rel(root, target)
+	if err != nil || filepath.IsAbs(relative) {
+		return false
+	}
+	return relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))
+}

internal/engine/glob.go

@@ -0,0 +1,205 @@
+package engine
+
+import (
+	"errors"
+	"io"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+const globReadBatch = 128
+
+type globCandidate struct {
+	absolute string
+	relative string
+}
+
+func (s *importTraversal) expandImportGlob(basePath string, declaration importDeclaration) ([]string, []Diagnostic) {
+	location := declaration.location
+	segments, valid := validGlobPattern(declaration.glob)
+	if !valid {
+		return nil, []Diagnostic{importDiagnostic(CodeImportInvalid, "import glob pattern is invalid or uses recursive ** syntax", &location)}
+	}
+
+	candidates := []globCandidate{{absolute: basePath}}
+	for index, segment := range segments {
+		last := index == len(segments)-1
+		literal, patterned := globLiteralSegment(segment)
+		var next []globCandidate
+		for _, candidate := range candidates {
+			var names []string
+			if patterned {
+				matched, diagnostics := s.readGlobMatches(candidate.absolute, segment, location)
+				if len(diagnostics) != 0 {
+					return nil, diagnostics
+				}
+				names = matched
+			} else {
+				names = []string{literal}
+			}
+			for _, name := range names {
+				absolute := filepath.Join(candidate.absolute, filepath.FromSlash(name))
+				relative := path.Join(candidate.relative, name)
+				if !containedPath(s.rootPath, filepath.Clean(absolute)) {
+					return nil, []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "glob traversal is outside the configuration root", &location)}
+				}
+				canonical, err := canonicalExistingPath(absolute)
+				if err != nil {
+					if errors.Is(err, fs.ErrNotExist) && !patterned {
+						continue
+					}
+					return nil, []Diagnostic{globFilesystemDiagnostic(err, "glob match could not be canonicalized", location)}
+				}
+				if !containedPath(s.rootPath, canonical) {
+					return nil, []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "glob traversal resolves outside the configuration root", &location)}
+				}
+				if last {
+					next = append(next, globCandidate{absolute: canonical, relative: relative})
+					if len(s.sources)+len(next) > s.limits.sources {
+						return nil, []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "glob matches exceed the remaining source-count limit", &location)}
+					}
+					continue
+				}
+				info, err := os.Stat(canonical)
+				if err != nil {
+					return nil, []Diagnostic{globFilesystemDiagnostic(err, "glob traversal target could not be inspected", location)}
+				}
+				if info.IsDir() {
+					next = append(next, globCandidate{absolute: canonical, relative: relative})
+				}
+			}
+		}
+		candidates = next
+		if len(candidates) == 0 {
+			return nil, nil
+		}
+	}
+
+	matches := make([]string, len(candidates))
+	for index, candidate := range candidates {
+		matches[index] = candidate.relative
+	}
+	slices.Sort(matches)
+	return matches, nil
+}
+
+func (s *importTraversal) readGlobMatches(directory, pattern string, location Location) ([]string, []Diagnostic) {
+	canonical, err := canonicalExistingPath(directory)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return nil, nil
+		}
+		return nil, []Diagnostic{globFilesystemDiagnostic(err, "glob directory could not be canonicalized", location)}
+	}
+	if !containedPath(s.rootPath, canonical) {
+		return nil, []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "glob directory resolves outside the configuration root", &location)}
+	}
+	relative, err := filepath.Rel(s.rootPath, canonical)
+	if err != nil || filepath.IsAbs(relative) || relative == ".." || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
+		return nil, []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "glob directory could not be addressed inside the configuration root", &location)}
+	}
+	directoryFile, err := s.root.Open(relative)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return nil, nil
+		}
+		return nil, []Diagnostic{globFilesystemDiagnostic(err, "glob directory could not be opened", location)}
+	}
+
+	var matches []string
+	for {
+		entries, readErr := directoryFile.ReadDir(globReadBatch)
+		for _, entry := range entries {
+			s.usedEntries++
+			if s.usedEntries > s.limits.entries {
+				_ = directoryFile.Close()
+				return nil, []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "glob traversal exceeds the directory-entry visit limit", &location)}
+			}
+			matched, matchErr := path.Match(pattern, entry.Name())
+			if matchErr != nil {
+				_ = directoryFile.Close()
+				return nil, []Diagnostic{importDiagnostic(CodeImportInvalid, "import glob pattern is invalid", &location)}
+			}
+			if matched {
+				matches = append(matches, entry.Name())
+			}
+		}
+		if errors.Is(readErr, io.EOF) {
+			break
+		}
+		if readErr != nil {
+			_ = directoryFile.Close()
+			return nil, []Diagnostic{globFilesystemDiagnostic(readErr, "glob directory could not be read", location)}
+		}
+	}
+	if err := directoryFile.Close(); err != nil {
+		return nil, []Diagnostic{globFilesystemDiagnostic(err, "glob directory could not be closed", location)}
+	}
+	slices.Sort(matches)
+	return matches, nil
+}
+
+func validGlobPattern(pattern string) ([]string, bool) {
+	if !validImportPath(pattern) {
+		return nil, false
+	}
+	segments := strings.Split(pattern, "/")
+	for _, segment := range segments {
+		if segment == "" || hasRecursiveStars(segment) {
+			return nil, false
+		}
+		if _, err := path.Match(segment, ""); err != nil {
+			return nil, false
+		}
+	}
+	return segments, true
+}
+
+func hasRecursiveStars(segment string) bool {
+	inClass := false
+	for index := 0; index < len(segment); index++ {
+		switch segment[index] {
+		case '\\':
+			index++
+		case '[':
+			inClass = true
+		case ']':
+			inClass = false
+		case '*':
+			if !inClass && index+1 < len(segment) && segment[index+1] == '*' {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func globLiteralSegment(segment string) (string, bool) {
+	var literal strings.Builder
+	for index := 0; index < len(segment); index++ {
+		switch segment[index] {
+		case '*', '?', '[':
+			return "", true
+		case '\\':
+			index++
+			if index < len(segment) {
+				literal.WriteByte(segment[index])
+			}
+		default:
+			literal.WriteByte(segment[index])
+		}
+	}
+	return literal.String(), false
+}
+
+func globFilesystemDiagnostic(err error, message string, location Location) Diagnostic {
+	code := CodeImportRead
+	if errors.Is(err, fs.ErrPermission) {
+		code = CodeImportPermission
+	}
+	return importDiagnostic(code, message, &location)
+}

internal/engine/glob_test.go

@@ -0,0 +1,273 @@
+package engine
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"testing"
+)
+
+func TestLoadGlobImportsUseLexicalDeclarationOrderAndNestedDFS(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - glob: fragments/*.yml
+    - path: after.yml
+items: {root: root}
+`)
+	aPath := writeImportFile(t, directory, "fragments/a.yml", `configkit:
+  imports: [{path: nested/child.yml}]
+items: {alpha: alpha}
+`)
+	childPath := writeImportFile(t, directory, "fragments/nested/child.yml", "items: {child: child}\n")
+	bPath := writeImportFile(t, directory, "fragments/b.yml", "items: {beta: beta}\n")
+	afterPath := writeImportFile(t, directory, "after.yml", "items: {after: after}\n")
+
+	var previous []SourceInfo
+	for run := 0; run < 2; run++ {
+		result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		if err != nil {
+			t.Fatal(err)
+		}
+		wantItems := map[string]string{"root": "root", "alpha": "alpha", "child": "child", "beta": "beta", "after": "after"}
+		if !reflect.DeepEqual(result.Config.Items, wantItems) {
+			t.Fatalf("items = %#v, want %#v", result.Config.Items, wantItems)
+		}
+		sources := result.Sources()
+		wantPaths := []string{
+			canonicalTestPath(t, mainPath), canonicalTestPath(t, aPath),
+			canonicalTestPath(t, childPath), canonicalTestPath(t, bPath),
+			canonicalTestPath(t, afterPath),
+		}
+		gotPaths := make([]string, len(sources))
+		for index, source := range sources {
+			gotPaths[index] = source.Path
+		}
+		if !reflect.DeepEqual(gotPaths, wantPaths) {
+			t.Fatalf("source paths = %#v, want %#v", gotPaths, wantPaths)
+		}
+		if run != 0 && !reflect.DeepEqual(sources, previous) {
+			t.Fatalf("repeated traversal changed sources: %#v != %#v", sources, previous)
+		}
+		previous = sources
+	}
+}
+
+func TestLoadGlobImportsSupportEscapesClassesAndExplicitConfD(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - glob: 'conf.d/literal\*.yml'
+    - glob: 'conf.d/item-[ab].yml'
+    - glob: 'conf.d/question?.yml'
+items: {root: root}
+`)
+	writeImportFile(t, directory, "conf.d/literal*.yml", "items: {literal: literal}\n")
+	writeImportFile(t, directory, "conf.d/item-b.yml", "items: {b: b}\n")
+	writeImportFile(t, directory, "conf.d/item-a.yml", "items: {a: a}\n")
+	writeImportFile(t, directory, "conf.d/question1.yml", "items: {question: question}\n")
+
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := map[string]string{"root": "root", "literal": "literal", "a": "a", "b": "b", "question": "question"}; !reflect.DeepEqual(result.Config.Items, want) {
+		t.Fatalf("items = %#v, want %#v", result.Config.Items, want)
+	}
+
+	ignoredPath := writeImportFile(t, directory, "conf.d/not-discovered.yml", "unknown: value\n")
+	_ = ignoredPath
+	plainPath := writeImportFile(t, directory, "plain.yml", "items: {root: only}\n")
+	plain, err := testLoad[importTestConfig](File(plainPath), Options[importTestConfig]{Imports: true})
+	if err != nil || len(plain.Sources()) != 1 || plain.Config.Items["root"] != "only" {
+		t.Fatalf("implicit discovery result = %#v, %v", plain, err)
+	}
+}
+
+func TestLoadGlobImportsRejectInvalidAndUnmatchedPatterns(t *testing.T) {
+	tests := []struct {
+		name    string
+		pattern string
+		code    Code
+	}{
+		{name: "bad class", pattern: "empty/[", code: CodeImportInvalid},
+		{name: "recursive star segment", pattern: "empty/**/value.yml", code: CodeImportInvalid},
+		{name: "recursive adjacent stars", pattern: "empty/value**.yml", code: CodeImportInvalid},
+		{name: "trailing separator", pattern: "empty/", code: CodeImportInvalid},
+		{name: "absolute", pattern: "/tmp/*.yml", code: CodeImportInvalid},
+		{name: "URL", pattern: "https://example.invalid/*.yml", code: CodeImportInvalid},
+		{name: "missing parent escape", pattern: "../missing/*.yml", code: CodeImportOutsideRoot},
+		{name: "unmatched", pattern: "empty/*.yml", code: CodeImportMissing},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			directory := t.TempDir()
+			if err := os.Mkdir(filepath.Join(directory, "empty"), 0o755); err != nil {
+				t.Fatal(err)
+			}
+			mainPath := writeGlobRoot(t, directory, test.pattern, false)
+			requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, test.code)
+		})
+	}
+
+	directory := t.TempDir()
+	if err := os.Mkdir(filepath.Join(directory, "empty"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	mainPath := writeGlobRoot(t, directory, "empty/*.yml", true)
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	if err != nil || len(result.Sources()) != 1 {
+		t.Fatalf("optional unmatched glob = %#v, %v", result, err)
+	}
+}
+
+func TestLoadGlobImportsPreserveIdentityAndFileRules(t *testing.T) {
+	t.Run("overlapping declarations", func(t *testing.T) {
+		directory := t.TempDir()
+		writeImportFile(t, directory, "conf/value.yml", "items: {value: value}\n")
+		mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - glob: conf/*.yml
+    - glob: conf/value.*
+`)
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportRepeated)
+	})
+
+	t.Run("matched directory", func(t *testing.T) {
+		directory := t.TempDir()
+		if err := os.MkdirAll(filepath.Join(directory, "conf/matched.yml"), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		mainPath := writeGlobRoot(t, directory, "conf/*.yml", true)
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeSourceNotRegular)
+	})
+
+	t.Run("hard links stay distinct", func(t *testing.T) {
+		directory := t.TempDir()
+		one := writeImportFile(t, directory, "conf/one.yml", "items: {same: value}\n")
+		if err := os.Link(one, filepath.Join(directory, "conf/two.yml")); err != nil {
+			t.Skipf("hard links unavailable: %v", err)
+		}
+		mainPath := writeGlobRoot(t, directory, "conf/*.yml", false)
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeComposeConflict)
+	})
+}
+
+func TestLoadGlobImportsConfineSymlinkDirectories(t *testing.T) {
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+		t.Skip("initial filesystem contract covers Linux and macOS")
+	}
+	t.Run("contained absolute target", func(t *testing.T) {
+		root := t.TempDir()
+		target := filepath.Join(root, "target")
+		writeImportFile(t, target, "value.yml", "items: {linked: linked}\n")
+		if err := os.Symlink(target, filepath.Join(root, "linked")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeGlobRoot(t, root, "linked/*.yml", false)
+		result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		if err != nil || result.Config.Items["linked"] != "linked" {
+			t.Fatalf("contained directory symlink = %#v, %v", result, err)
+		}
+	})
+
+	t.Run("escaping target", func(t *testing.T) {
+		root := t.TempDir()
+		outside := t.TempDir()
+		writeImportFile(t, outside, "value.yml", "items: {escaped: escaped}\n")
+		if err := os.Symlink(outside, filepath.Join(root, "linked")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeGlobRoot(t, root, "linked/*.yml", true)
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportOutsideRoot)
+	})
+}
+
+func TestOptionalGlobDoesNotSuppressDirectoryPermissionFailure(t *testing.T) {
+	directory := t.TempDir()
+	locked := filepath.Join(directory, "locked")
+	if err := os.Mkdir(locked, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chmod(locked, 0); err != nil {
+		t.Skipf("cannot create unreadable directory fixture: %v", err)
+	}
+	defer func() { _ = os.Chmod(locked, 0o700) }()
+	if opened, err := os.Open(locked); err == nil {
+		_ = opened.Close()
+		t.Skip("filesystem does not enforce the unreadable-directory fixture")
+	}
+	mainPath := writeGlobRoot(t, directory, "locked/*.yml", true)
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportPermission)
+}
+
+func TestGlobTraversalBoundsNonmatchesAndAcceptedCandidates(t *testing.T) {
+	directory := t.TempDir()
+	for _, name := range []string{"one.txt", "two.txt", "three.txt"} {
+		writeImportFile(t, directory, "many/"+name, "ignored\n")
+	}
+	mainPath := writeGlobRoot(t, directory, "many/*.yml", true)
+	main := parseImportMain(t, mainPath)
+	limits := defaultImportLimits()
+	limits.entries = 2
+	_, _, diagnostics := loadImportedDocuments(File(mainPath), nil, main, nil, limits)
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeImportLimitExceeded {
+		t.Fatalf("entry-budget diagnostics = %#v", diagnostics)
+	}
+
+	for _, name := range []string{"a.yml", "b.yml"} {
+		writeImportFile(t, directory, "matches/"+name, "items: {"+name[:1]+": value}\n")
+	}
+	mainPath = writeGlobRoot(t, directory, "matches/*.yml", false)
+	main = parseImportMain(t, mainPath)
+	limits = defaultImportLimits()
+	limits.sources = 2
+	_, _, diagnostics = loadImportedDocuments(File(mainPath), nil, main, nil, limits)
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeImportLimitExceeded {
+		t.Fatalf("candidate-budget diagnostics = %#v", diagnostics)
+	}
+}
+
+func TestFilesystemContextIsValidatedWithoutImportsOrActiveOverlay(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", "items: {root: root}\n")
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{
+		Overlay: "default", Filesystem: &FilesystemContext{Root: directory},
+	})
+	if err != nil || result.Config.Items["root"] != "root" {
+		t.Fatalf("file filesystem context = %#v, %v", result, err)
+	}
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Filesystem: &FilesystemContext{BaseDir: directory, Root: directory}}, CodeOptionsInvalid)
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Filesystem: &FilesystemContext{Root: filepath.Join(directory, "missing")}}, CodeImportInvalid)
+
+	input := Bytes("memory.yml", []byte("items: {root: memory}\n"))
+	result, err = testLoad[importTestConfig](input, Options[importTestConfig]{Filesystem: &FilesystemContext{BaseDir: directory, Root: directory}})
+	if err != nil || result.Config.Items["root"] != "memory" {
+		t.Fatalf("byte filesystem context = %#v, %v", result, err)
+	}
+	requireLoadCode(t, Bytes("memory.yml", []byte("{}\n")), Options[importTestConfig]{Filesystem: &FilesystemContext{BaseDir: directory}}, CodeOptionsInvalid)
+	defaultsOnly, err := testLoad[importTestConfig](NoSource(), Options[importTestConfig]{Overlay: "default"})
+	if err != nil || defaultsOnly == nil {
+		t.Fatalf("default overlay with NoSource = %#v, %v", defaultsOnly, err)
+	}
+
+	if runtime.GOOS == "linux" || runtime.GOOS == "darwin" {
+		selectedLink := filepath.Join(directory, "selected-link.yml")
+		if err := os.Symlink(mainPath, selectedLink); err == nil {
+			linked, err := testLoad[importTestConfig](File(selectedLink), Options[importTestConfig]{Filesystem: &FilesystemContext{Root: directory}})
+			if err != nil || linked.Sources()[0].Path != canonicalTestPath(t, mainPath) {
+				t.Fatalf("selected symlink identity = %#v, %v", linked, err)
+			}
+		}
+	}
+}
+
+func writeGlobRoot(t *testing.T, directory, pattern string, optional bool) string {
+	t.Helper()
+	optionalLine := ""
+	if optional {
+		optionalLine = "\n      optional: true"
+	}
+	return writeImportFile(t, directory, "main.yml", "configkit:\n  imports:\n    - glob: '"+pattern+"'"+optionalLine+"\n")
+}

internal/engine/history.go

@@ -0,0 +1,276 @@
+package engine
+
+import (
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+const historyNodeLimit = 4_000_000
+
+// History applications borrow immutable policy-validated input trees. Metadata
+// records answer presence and origin queries; replay reconstructs value changes.
+// Replay reconciles with canonical decoding before domain resolution so both
+// contracts agree on the effective result without retaining a tree per field.
+type historyApplication struct {
+	layer  Layer
+	path   Path
+	value  *document.Node
+	origin Origin
+}
+
+func cloneHistoryApplications(values []historyApplication) []historyApplication {
+	if values == nil {
+		return nil
+	}
+	cloned := make([]historyApplication, len(values))
+	for index, value := range values {
+		cloned[index] = historyApplication{
+			layer: value.layer, path: value.path.clone(), value: value.value,
+			origin: cloneOrigin(value.origin),
+		}
+	}
+	return cloned
+}
+
+func applicationOperationPath(application historyApplication, query Path) (Path, bool) {
+	if !application.path.valid() || application.value == nil {
+		return Path{}, false
+	}
+	if application.path.String() != "" {
+		if pathsIntersect(application.path, query) {
+			return application.path.clone(), true
+		}
+		return Path{}, false
+	}
+	if len(query.segments) == 0 {
+		return Path{}, true
+	}
+	for length := 1; length <= len(query.segments); length++ {
+		prefix := Path{segments: clonePathSegments(query.segments[:length], 0)}
+		node, present := documentAtPath(application.value, prefix)
+		if !present {
+			return Path{}, false
+		}
+		if length == len(query.segments) || node.Kind != document.Mapping {
+			return prefix, true
+		}
+	}
+	return Path{}, false
+}
+
+func historyApplicationOrigin(application historyApplication, operationPath Path) Origin {
+	if application.origin.Layer != "" {
+		return cloneOrigin(application.origin)
+	}
+	origin := Origin{Layer: application.layer}
+	relative, ok := relativeHistoryPath(application.path, operationPath)
+	if !ok {
+		return origin
+	}
+	if node, present := documentAtPath(application.value, relative); present {
+		origin.Locations = []Location{publicLocation(node.Location)}
+	}
+	return origin
+}
+
+func relativeHistoryPath(root, path Path) (Path, bool) {
+	if !pathContains(root, path) {
+		return Path{}, false
+	}
+	return Path{segments: clonePathSegments(path.segments[len(root.segments):], 0)}, true
+}
+
+func pathsIntersect(left, right Path) bool {
+	return pathContains(left, right) || pathContains(right, left)
+}
+
+func applyHistoryApplication(root **document.Node, application historyApplication) {
+	if application.path.String() == "" {
+		mergeHistoryDocument(root, application.value)
+		return
+	}
+	mergeHistoryAtPath(root, application.path, application.value)
+}
+
+func mergeHistoryDocument(target **document.Node, incoming *document.Node) {
+	if incoming == nil {
+		return
+	}
+	if *target == nil || (*target).Kind != document.Mapping || incoming.Kind != document.Mapping {
+		*target = document.Clone(incoming)
+		return
+	}
+	for _, entry := range incoming.Mapping {
+		position := documentEntryIndex((*target).Mapping, entry.Key)
+		if position < 0 {
+			cloned := entry
+			cloned.Value = document.Clone(entry.Value)
+			(*target).Mapping = append((*target).Mapping, cloned)
+			continue
+		}
+		mergeHistoryDocument(&(*target).Mapping[position].Value, entry.Value)
+	}
+}
+
+func mergeHistoryAtPath(root **document.Node, path Path, incoming *document.Node) {
+	if root == nil || *root == nil || len(path.segments) == 0 {
+		mergeHistoryDocument(root, incoming)
+		return
+	}
+	current := *root
+	for index, segment := range path.segments {
+		if current.Kind != document.Mapping || segment.kind == pathSegmentIndex {
+			return
+		}
+		position := documentEntryIndex(current.Mapping, segment.key)
+		if index == len(path.segments)-1 {
+			if position < 0 {
+				current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: document.Clone(incoming)})
+			} else {
+				mergeHistoryDocument(&current.Mapping[position].Value, incoming)
+			}
+			return
+		}
+		if position < 0 {
+			child := &document.Node{Kind: document.Mapping}
+			current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: child})
+			current = child
+		} else {
+			current = current.Mapping[position].Value
+		}
+	}
+}
+
+// Resolution records describe one before/final transformation, not assignment
+// order. A parent already carries its descendants' final values; merge overlapping
+// intent into that event rather than replay a child assignment a second time.
+func coalescedResolutionSnapshots(snapshots []resolutionSnapshot) []resolutionSnapshot {
+	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	for _, snapshot := range snapshots {
+		merged := false
+		for i := range groups {
+			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
+				continue
+			}
+			for _, reason := range snapshot.change.Reasons {
+				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
+			}
+			for _, dependency := range snapshot.change.Dependencies {
+				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
+			}
+			if snapshot.change.Origin.Operation == ChangeNormalization {
+				groups[i].change.Origin.Operation = ChangeNormalization
+			}
+			merged = true
+			break
+		}
+		if !merged {
+			snapshot.change = cloneChange(snapshot.change)
+			groups = append(groups, snapshot)
+		}
+	}
+	return groups
+}
+
+func replaceHistoryPath(root **document.Node, path Path, replacement *document.Node) {
+	if root == nil || *root == nil {
+		return
+	}
+	if len(path.segments) == 0 {
+		*root = document.Clone(replacement)
+		return
+	}
+	current := *root
+	for index, segment := range path.segments {
+		last := index == len(path.segments)-1
+		switch current.Kind {
+		case document.Mapping:
+			if segment.kind == pathSegmentIndex {
+				return
+			}
+			position := documentEntryIndex(current.Mapping, segment.key)
+			if position < 0 {
+				if replacement == nil {
+					return
+				}
+				child := &document.Node{Kind: document.Mapping}
+				if last {
+					child = document.Clone(replacement)
+				}
+				current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: child})
+				if last {
+					return
+				}
+				current = child
+				continue
+			}
+			if last {
+				if replacement == nil {
+					current.Mapping = append(current.Mapping[:position], current.Mapping[position+1:]...)
+				} else {
+					current.Mapping[position].Value = document.Clone(replacement)
+				}
+				return
+			}
+			current = current.Mapping[position].Value
+		case document.Sequence:
+			position, ok := schemaIndex(segment)
+			if !ok || position >= len(current.Sequence) {
+				return
+			}
+			if last {
+				if replacement != nil {
+					current.Sequence[position] = document.Clone(replacement)
+				}
+				return
+			}
+			current = current.Sequence[position]
+		default:
+			return
+		}
+	}
+}
+
+func historyNodesWithinLimit(baseline, input, final *document.Node, applications []historyApplication, resolutions []resolutionSnapshot) bool {
+	return historyNodesWithin(historyNodeLimit, baseline, input, final, applications, resolutions)
+}
+
+func historyNodesWithin(limit int, baseline, input, final *document.Node, applications []historyApplication, resolutions []resolutionSnapshot) bool {
+	seen := make(map[*document.Node]bool)
+	count := 0
+	var visit func(*document.Node) bool
+	visit = func(node *document.Node) bool {
+		if node == nil || seen[node] {
+			return true
+		}
+		seen[node] = true
+		count++
+		if count > limit {
+			return false
+		}
+		for _, entry := range node.Mapping {
+			if !visit(entry.Value) {
+				return false
+			}
+		}
+		for _, child := range node.Sequence {
+			if !visit(child) {
+				return false
+			}
+		}
+		return true
+	}
+	if !visit(baseline) || !visit(input) || !visit(final) {
+		return false
+	}
+	for _, application := range applications {
+		if !visit(application.value) {
+			return false
+		}
+	}
+	for _, resolution := range resolutions {
+		if !visit(resolution.before) || !visit(resolution.after) {
+			return false
+		}
+	}
+	return true
+}

internal/engine/imports.go

@@ -0,0 +1,324 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+	yamladapter "gitea.maximumdirect.net/eric/ConfigKit/internal/yaml"
+)
+
+const (
+	maxImportDepth   = 64
+	maxImportSources = 1024
+	maxGlobEntries   = 1_000_000
+)
+
+type importLimits struct {
+	depth   int
+	sources int
+	bytes   int64
+	nodes   int
+	entries int
+}
+
+func defaultImportLimits() importLimits {
+	return importLimits{
+		depth: maxImportDepth, sources: maxImportSources,
+		bytes: maxTotalBytes, nodes: maxDocumentNodes, entries: maxGlobEntries,
+	}
+}
+
+type importRoute struct {
+	canonical string
+	locations []Location
+}
+
+type importTraversal struct {
+	rootPath string
+	root     *os.Root
+	limits   importLimits
+	rule     *VersionRule
+
+	documents   []*document.Node
+	sources     []SourceInfo
+	active      map[string]int
+	visited     map[string]importRoute
+	stack       []importRoute
+	usedBytes   int64
+	usedNodes   int
+	usedEntries int
+}
+
+func loadImportedDocuments(source Source, context *FilesystemContext, main parsedSource, rule *VersionRule, limits importLimits) (*composedDocument, []SourceInfo, []Diagnostic) {
+	rootPath, basePath, mainPath, diagnostic := importFilesystem(source, context, main)
+	if diagnostic != nil {
+		return nil, sourceInfos(main.source), []Diagnostic{*diagnostic}
+	}
+	root, err := os.OpenRoot(rootPath)
+	if err != nil {
+		diagnostic := globFilesystemDiagnostic(err, "configuration root could not be opened", Location{})
+		diagnostic.Primary = nil
+		return nil, sourceInfos(main.source), []Diagnostic{diagnostic}
+	}
+
+	mainInfo := cloneSourceInfo(*main.source)
+	if mainPath != "" {
+		mainInfo.Path = mainPath
+	}
+	state := importTraversal{
+		rootPath: rootPath, root: root, limits: limits, rule: rule,
+		documents: make([]*document.Node, 0, 1),
+		sources:   []SourceInfo{mainInfo},
+		active:    make(map[string]int), visited: make(map[string]importRoute),
+		usedBytes: main.bytes, usedNodes: countInputNodes(main.document),
+	}
+	if diagnostic := state.checkInitialLimits(); diagnostic != nil {
+		_ = root.Close()
+		return nil, cloneSourceInfos(state.sources), []Diagnostic{*diagnostic}
+	}
+
+	mainIdentity := mainPath
+	if mainIdentity == "" {
+		mainIdentity = "<selected-source>"
+	}
+	mainRoute := importRoute{canonical: mainIdentity}
+	state.active[mainIdentity] = 0
+	state.visited[mainIdentity] = mainRoute
+	state.stack = append(state.stack, mainRoute)
+	body, declarations, diagnostics := splitImportDirectives(main.document)
+	if len(diagnostics) == 0 {
+		state.documents = append(state.documents, body)
+		diagnostics = state.walkDeclarations(basePath, declarations, 0)
+	}
+
+	closeErr := root.Close()
+	if len(diagnostics) != 0 {
+		return nil, cloneSourceInfos(state.sources), diagnostics
+	}
+	if closeErr != nil {
+		return nil, cloneSourceInfos(state.sources), []Diagnostic{importDiagnostic(CodeImportRead, "configuration root could not be closed", nil)}
+	}
+	composed, diagnostics := composeDocuments(state.documents...)
+	if composed != nil {
+		composed.inputBytes = state.usedBytes
+		composed.inputNodes = state.usedNodes
+	}
+	return composed, cloneSourceInfos(state.sources), diagnostics
+}
+
+func (s *importTraversal) checkInitialLimits() *Diagnostic {
+	if s.limits.sources < 1 {
+		value := importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the source-count limit", nil)
+		return &value
+	}
+	if s.usedBytes > s.limits.bytes {
+		value := importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the aggregate byte limit", nil)
+		return &value
+	}
+	if s.usedNodes > s.limits.nodes {
+		value := importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the aggregate node limit", nil)
+		return &value
+	}
+	return nil
+}
+
+func (s *importTraversal) walkDeclarations(basePath string, declarations []importDeclaration, depth int) []Diagnostic {
+	for _, declaration := range declarations {
+		if declaration.glob != "" {
+			matches, diagnostics := s.expandImportGlob(basePath, declaration)
+			if len(diagnostics) != 0 {
+				return diagnostics
+			}
+			if len(matches) == 0 {
+				if declaration.optional {
+					continue
+				}
+				location := declaration.location
+				return []Diagnostic{importDiagnostic(CodeImportMissing, "required import glob matched no files", &location)}
+			}
+			for _, match := range matches {
+				matched := declaration
+				matched.path = match
+				matched.glob = ""
+				if diagnostics := s.visitPath(basePath, matched, depth+1); len(diagnostics) != 0 {
+					return diagnostics
+				}
+			}
+			continue
+		}
+		if diagnostics := s.visitPath(basePath, declaration, depth+1); len(diagnostics) != 0 {
+			return diagnostics
+		}
+	}
+	return nil
+}
+
+func (s *importTraversal) visitPath(basePath string, declaration importDeclaration, depth int) []Diagnostic {
+	location := declaration.location
+	if depth > s.limits.depth {
+		return []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the active import-depth limit", &location)}
+	}
+	if !validImportPath(declaration.path) {
+		return []Diagnostic{importDiagnostic(CodeImportInvalid, "import path must be a nonempty slash-relative path without a network scheme", &location)}
+	}
+
+	candidate := filepath.Join(basePath, filepath.FromSlash(path.Clean(declaration.path)))
+	if !containedPath(s.rootPath, filepath.Clean(candidate)) {
+		return []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "import target is outside the configuration root", &location)}
+	}
+	canonical, err := canonicalExistingPath(candidate)
+	if err != nil {
+		if declaration.optional && errors.Is(err, fs.ErrNotExist) {
+			return nil
+		}
+		code := CodeImportInvalid
+		message := "import target could not be canonicalized"
+		if errors.Is(err, fs.ErrNotExist) {
+			code, message = CodeImportMissing, "required import target does not exist"
+		} else if errors.Is(err, fs.ErrPermission) {
+			message = "import target cannot be accessed"
+		}
+		return []Diagnostic{importDiagnostic(code, message, &location)}
+	}
+	if !containedPath(s.rootPath, canonical) {
+		return []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "import target resolves outside the configuration root", &location)}
+	}
+
+	currentRoute := s.currentRoute(location)
+	if activeIndex, ok := s.active[canonical]; ok {
+		cycle := append([]importRoute(nil), s.stack[activeIndex:]...)
+		return []Diagnostic{importCycleDiagnostic(canonical, location, cycle)}
+	}
+	if previous, ok := s.visited[canonical]; ok {
+		return []Diagnostic{importRepeatedDiagnostic(location, previous, currentRoute)}
+	}
+	if len(s.sources)+1 > s.limits.sources {
+		return []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the source-count limit", &location)}
+	}
+
+	relative, err := filepath.Rel(s.rootPath, canonical)
+	if err != nil || filepath.IsAbs(relative) || relative == ".." || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
+		return []Diagnostic{importDiagnostic(CodeImportOutsideRoot, "import target could not be addressed inside the configuration root", &location)}
+	}
+	sourceID := "source-" + strconv.Itoa(len(s.sources)+1)
+	info := SourceInfo{ID: sourceID, Label: declaration.path, Path: canonical, Layer: LayerBase, ImportedFrom: &location}
+	s.sources = append(s.sources, info)
+	data, skipped, diagnostic := s.readImport(relative, sourceID, declaration.optional)
+	if diagnostic != nil {
+		return []Diagnostic{*diagnostic}
+	}
+	if skipped {
+		s.sources = s.sources[:len(s.sources)-1]
+		return nil
+	}
+
+	root, issues := yamladapter.Parse(bytes.NewReader(data), sourceID, yamladapter.Limits{
+		Depth: maxDocumentDepth, Nodes: maxDocumentNodes,
+	})
+	if len(issues) != 0 {
+		return parserDiagnostics(sourceID, issues)
+	}
+	nodeCount := countInputNodes(root)
+	if s.usedNodes+nodeCount > s.limits.nodes {
+		return []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the aggregate node limit", &location)}
+	}
+	s.usedNodes += nodeCount
+
+	body, declarations, diagnostics := splitImportDirectives(root)
+	if len(diagnostics) != 0 {
+		return diagnostics
+	}
+	if versionNode := fragmentVersionClaim(body, s.rule); versionNode != nil {
+		versionLocation := publicLocation(versionNode.Location)
+		return []Diagnostic{{
+			Code: CodeImportVersion, Severity: SeverityError, Path: s.rule.Path.clone(),
+			Message: "imported fragments cannot contribute to the schema-version path", Primary: &versionLocation,
+		}}
+	}
+
+	route := importRoute{canonical: canonical, locations: currentRoute.locations}
+	s.documents = append(s.documents, body)
+	s.active[canonical] = len(s.stack)
+	s.visited[canonical] = route
+	s.stack = append(s.stack, route)
+	diagnostics = s.walkDeclarations(filepath.Dir(canonical), declarations, depth)
+	delete(s.active, canonical)
+	s.stack = s.stack[:len(s.stack)-1]
+	return diagnostics
+}
+
+func (s *importTraversal) readImport(relative, sourceID string, optional bool) ([]byte, bool, *Diagnostic) {
+	remaining := s.limits.bytes - s.usedBytes
+	limit := min(int64(maxSourceBytes), remaining)
+	if limit < 0 {
+		limit = 0
+	}
+	data, failure := readRegularFile(relative, s.root.Stat, s.root.Open, limit)
+	if failure != nil {
+		if optional && failure.missingTarget {
+			return nil, true, nil
+		}
+		value := sourceReadDiagnostic(failure, sourceID, CodeImportLimitExceeded, "configuration exceeds a source or aggregate byte limit")
+		return nil, false, &value
+	}
+	s.usedBytes += int64(len(data))
+	return data, false, nil
+}
+
+func (s *importTraversal) currentRoute(location Location) importRoute {
+	locations := make([]Location, 0, len(s.stack)+1)
+	for _, route := range s.stack {
+		if len(route.locations) != 0 {
+			locations = append(locations, route.locations[len(route.locations)-1])
+		}
+	}
+	locations = append(locations, location)
+	return importRoute{locations: locations}
+}
+
+func sourceInfos(source *SourceInfo) []SourceInfo {
+	if source == nil {
+		return nil
+	}
+	return []SourceInfo{cloneSourceInfo(*source)}
+}
+
+func importDiagnostic(code Code, message string, location *Location) Diagnostic {
+	return Diagnostic{Code: code, Severity: SeverityError, Message: message, Primary: cloneLocation(location)}
+}
+
+func importCycleDiagnostic(target string, location Location, cycle []importRoute) Diagnostic {
+	paths := make([]string, 0, len(cycle)+1)
+	related := make([]Location, 0, len(cycle))
+	for _, route := range cycle {
+		paths = append(paths, route.canonical)
+		if len(route.locations) != 0 {
+			related = append(related, route.locations[len(route.locations)-1])
+		}
+	}
+	paths = append(paths, target)
+	return Diagnostic{
+		Code: CodeImportCycle, Severity: SeverityError,
+		Message: "import cycle detected: " + strings.Join(paths, " -> "),
+		Primary: &location, Related: related,
+	}
+}
+
+func importRepeatedDiagnostic(location Location, previous, current importRoute) Diagnostic {
+	related := append([]Location(nil), previous.locations...)
+	if len(current.locations) > 1 {
+		related = append(related, current.locations[:len(current.locations)-1]...)
+	}
+	return Diagnostic{
+		Code: CodeImportRepeated, Severity: SeverityError,
+		Message: "configuration source is included by more than one import route",
+		Primary: &location, Related: related,
+	}
+}

internal/engine/imports_test.go

@@ -0,0 +1,488 @@
+package engine
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+type importTestConfig struct {
+	Settings struct {
+		Root   string `yaml:"root"`
+		First  string `yaml:"first"`
+		Nested string `yaml:"nested"`
+		Second string `yaml:"second"`
+	} `yaml:"settings"`
+	Version string            `yaml:"version"`
+	Items   map[string]string `yaml:"items"`
+}
+
+func TestLoadFormerDirectiveKeyIsApplicationData(t *testing.T) {
+	type config struct {
+		Legacy struct {
+			Imports []struct {
+				Path string `yaml:"path"`
+			} `yaml:"imports"`
+		} `yaml:"_configkit"`
+	}
+	for _, imports := range []bool{false, true} {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", "_configkit:\n  imports:\n    - path: nonexistent.yml\n")
+		result, err := testLoad[config](File(mainPath), Options[config]{Imports: imports})
+		if err != nil {
+			t.Fatalf("Imports=%v: %v", imports, err)
+		}
+		if len(result.Config.Legacy.Imports) != 1 || result.Config.Legacy.Imports[0].Path != "nonexistent.yml" || len(result.Sources()) != 1 {
+			t.Fatalf("Imports=%v: former directive was not retained as application data: %#v", imports, result)
+		}
+	}
+}
+
+func TestLoadTraversesPathImportsDepthFirstAndComposesOrigins(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - path: first.yml
+    - path: second.yml
+settings:
+  root: root
+`)
+	firstPath := writeImportFile(t, directory, "first.yml", `configkit:
+  imports:
+    - path: nested/third.yml
+settings:
+  first: first
+`)
+	thirdPath := writeImportFile(t, directory, "nested/third.yml", "settings:\n  nested: nested\n")
+	secondPath := writeImportFile(t, directory, "second.yml", "settings:\n  second: second\n")
+
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := result.Config.Settings; got.Root != "root" || got.First != "first" || got.Nested != "nested" || got.Second != "second" {
+		t.Fatalf("composed settings = %#v", got)
+	}
+	sources := result.Sources()
+	wantPaths := []string{canonicalTestPath(t, mainPath), canonicalTestPath(t, firstPath), canonicalTestPath(t, thirdPath), canonicalTestPath(t, secondPath)}
+	gotPaths := make([]string, len(sources))
+	for index, source := range sources {
+		gotPaths[index] = source.Path
+		if source.ID != "source-"+strconv.Itoa(index+1) {
+			t.Errorf("source %d ID = %q", index, source.ID)
+		}
+		if index > 0 && source.ImportedFrom == nil {
+			t.Errorf("source %d has no import location", index)
+		}
+	}
+	if !reflect.DeepEqual(gotPaths, wantPaths) {
+		t.Fatalf("source paths = %#v, want depth-first %#v", gotPaths, wantPaths)
+	}
+	info, ok := result.Metadata().Lookup(Keys("settings"))
+	if !ok || !info.Explicit || len(info.Origin.Locations) != 4 {
+		t.Fatalf("settings metadata = %#v, %v", info, ok)
+	}
+}
+
+func TestLoadImportsFromProfilesDirectoryAsBaseInput(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: profiles/shared.yml}]}\n")
+	writeImportFile(t, directory, "profiles/shared.yml", "settings: {root: imported}\n")
+
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	if err != nil || result.Config.Settings.Root != "imported" || len(result.Sources()) != 2 ||
+		result.Sources()[1].Layer != LayerBase {
+		t.Fatalf("profiles import = %#v, %v", result, err)
+	}
+}
+
+func TestLoadRejectsImportConflictsAndFragmentVersions(t *testing.T) {
+	t.Run("all duplicate claimants", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - path: one.yml
+    - path: two.yml
+    - path: three.yml
+`)
+		for index, name := range []string{"one.yml", "two.yml", "three.yml"} {
+			writeImportFile(t, directory, name, "settings:\n  root: "+string(rune('a'+index))+"\n")
+		}
+		loadError := requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeComposeConflict)
+		diagnostic := loadError.Diagnostics()[0]
+		if diagnostic.Path.String() != "/settings/root" || diagnostic.Primary == nil || len(diagnostic.Related) != 2 {
+			t.Fatalf("conflict diagnostic = %#v", diagnostic)
+		}
+	})
+
+	versionRule := &VersionRule{Path: Keys("settings", "version"), Check: func(Version, *Validation) error { return nil }}
+	for _, test := range []struct {
+		name     string
+		fragment string
+	}{
+		{name: "exact integer", fragment: "settings:\n  version: 4\n"},
+		{name: "ancestor scalar", fragment: "settings: blocked\n"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			directory := t.TempDir()
+			mainPath := writeImportFile(t, directory, "main.yml", "configkit:\n  imports:\n    - path: fragment.yml\n")
+			writeImportFile(t, directory, "fragment.yml", test.fragment)
+			loadError := requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true, Definition: Definition[importTestConfig]{Version: versionRule}}, CodeImportVersion)
+			diagnostic := loadError.Diagnostics()[0]
+			if diagnostic.Path.String() != "/settings/version" || diagnostic.Primary == nil || diagnostic.Primary.SourceID != "source-2" {
+				t.Fatalf("version placement diagnostic = %#v", diagnostic)
+			}
+		})
+	}
+}
+
+func TestLoadImportDirectiveValidationAndTemporaryGlobGate(t *testing.T) {
+	tests := []struct {
+		name string
+		body string
+		code Code
+	}{
+		{name: "directive kind", body: "configkit: []\n", code: CodeImportInvalid},
+		{name: "unknown directive field", body: "configkit: {unknown: true}\n", code: CodeImportInvalid},
+		{name: "imports kind", body: "configkit: {imports: {}}\n", code: CodeImportInvalid},
+		{name: "declaration kind", body: "configkit: {imports: [file.yml]}\n", code: CodeImportInvalid},
+		{name: "missing target", body: "configkit: {imports: [{optional: true}]}\n", code: CodeImportInvalid},
+		{name: "two targets", body: "configkit: {imports: [{path: a.yml, glob: '*.yml'}]}\n", code: CodeImportInvalid},
+		{name: "unknown declaration field", body: "configkit: {imports: [{path: a.yml, extra: true}]}\n", code: CodeImportInvalid},
+		{name: "optional kind", body: "configkit: {imports: [{path: a.yml, optional: 'yes'}]}\n", code: CodeImportInvalid},
+		{name: "nested directive", body: "nested: {configkit: {}}\n", code: CodeImportInvalid},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			directory := t.TempDir()
+			mainPath := writeImportFile(t, directory, "main.yml", test.body)
+			requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, test.code)
+		})
+	}
+}
+
+func TestLoadImportMissingContainmentAndRegularFileRules(t *testing.T) {
+	t.Run("optional missing", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports:
+    - path: missing.yml
+      optional: true
+settings: {root: retained}
+`)
+		result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		if err != nil || result.Config.Settings.Root != "retained" || len(result.Sources()) != 1 {
+			t.Fatalf("optional result = %#v, %v", result, err)
+		}
+	})
+
+	tests := []struct {
+		name  string
+		path  string
+		setup func(*testing.T, string)
+		code  Code
+	}{
+		{name: "required missing", path: "missing.yml", code: CodeImportMissing},
+		{name: "parent traversal", path: "../outside.yml", setup: func(t *testing.T, directory string) {
+			writeImportFile(t, filepath.Dir(directory), "outside.yml", "settings: {root: outside}\n")
+		}, code: CodeImportOutsideRoot},
+		{name: "directory", path: "directory", setup: func(t *testing.T, directory string) {
+			if err := os.Mkdir(filepath.Join(directory, "directory"), 0o755); err != nil {
+				t.Fatal(err)
+			}
+		}, code: CodeSourceNotRegular},
+		{name: "absolute", path: "/tmp/configkit.yml", code: CodeImportInvalid},
+		{name: "network URL", path: "https://example.invalid/config.yml", code: CodeImportInvalid},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			directory := t.TempDir()
+			if test.setup != nil {
+				test.setup(t, directory)
+			}
+			mainPath := writeImportFile(t, directory, "main.yml", "configkit:\n  imports:\n    - path: \""+test.path+"\"\n")
+			requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, test.code)
+		})
+	}
+}
+
+func TestLoadImportIdentityReportsCyclesAndRepeatedRoutes(t *testing.T) {
+	t.Run("cycle", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit:\n  imports: [{path: a.yml}]\n")
+		writeImportFile(t, directory, "a.yml", "configkit:\n  imports: [{path: b.yml}]\n")
+		writeImportFile(t, directory, "b.yml", "configkit:\n  imports: [{path: main.yml}]\n")
+		loadError := requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportCycle)
+		diagnostic := loadError.Diagnostics()[0]
+		if diagnostic.Primary == nil || len(diagnostic.Related) != 2 || !strings.Contains(diagnostic.Message, "main.yml") || !strings.Contains(diagnostic.Message, "a.yml") || !strings.Contains(diagnostic.Message, "b.yml") {
+			t.Fatalf("cycle diagnostic = %#v", diagnostic)
+		}
+	})
+
+	t.Run("diamond", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit:\n  imports: [{path: left.yml}, {path: right.yml}]\n")
+		writeImportFile(t, directory, "left.yml", "configkit:\n  imports: [{path: shared.yml}]\n")
+		writeImportFile(t, directory, "right.yml", "configkit:\n  imports: [{path: shared.yml}]\n")
+		writeImportFile(t, directory, "shared.yml", "settings: {root: shared}\n")
+		loadError := requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportRepeated)
+		diagnostic := loadError.Diagnostics()[0]
+		if diagnostic.Primary == nil || len(diagnostic.Related) < 3 {
+			t.Fatalf("repeated-route diagnostic = %#v", diagnostic)
+		}
+	})
+
+	t.Run("symlink aliases", func(t *testing.T) {
+		if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+			t.Skip("initial filesystem contract covers Linux and macOS")
+		}
+		directory := t.TempDir()
+		writeImportFile(t, directory, "target.yml", "settings: {root: target}\n")
+		if err := os.Symlink("target.yml", filepath.Join(directory, "first-link.yml")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		if err := os.Symlink("target.yml", filepath.Join(directory, "second-link.yml")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: first-link.yml}, {path: second-link.yml}]}\n")
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportRepeated)
+	})
+}
+
+func TestLoadImportsCanonicalSymlinksAndKeepsHardLinksDistinct(t *testing.T) {
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+		t.Skip("initial filesystem contract covers Linux and macOS")
+	}
+	t.Run("contained absolute symlink", func(t *testing.T) {
+		directory := t.TempDir()
+		target := writeImportFile(t, directory, "target.yml", "settings: {first: linked}\n")
+		if err := os.Symlink(target, filepath.Join(directory, "link.yml")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: link.yml}]}\n")
+		result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		if err != nil || result.Config.Settings.First != "linked" || result.Sources()[1].Path != canonicalTestPath(t, target) {
+			t.Fatalf("symlink result = %#v, %v", result, err)
+		}
+	})
+
+	t.Run("symlink escape", func(t *testing.T) {
+		root := t.TempDir()
+		outside := t.TempDir()
+		target := writeImportFile(t, outside, "outside.yml", "settings: {root: outside}\n")
+		if err := os.Symlink(target, filepath.Join(root, "escape.yml")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeImportFile(t, root, "main.yml", "configkit: {imports: [{path: escape.yml}]}\n")
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportOutsideRoot)
+	})
+
+	t.Run("hard links are path identities", func(t *testing.T) {
+		directory := t.TempDir()
+		one := writeImportFile(t, directory, "one.yml", "settings: {first: one}\n")
+		if err := os.Link(one, filepath.Join(directory, "two.yml")); err != nil {
+			t.Skipf("hard links unavailable: %v", err)
+		}
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: one.yml}, {path: two.yml}]}\n")
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeComposeConflict)
+	})
+
+	t.Run("canonicalization failure", func(t *testing.T) {
+		directory := t.TempDir()
+		if err := os.Symlink("loop.yml", filepath.Join(directory, "loop.yml")); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: loop.yml}]}\n")
+		requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportInvalid)
+	})
+}
+
+func TestLoadByteAndReaderImportsRequireExplicitFilesystemContext(t *testing.T) {
+	directory := t.TempDir()
+	writeImportFile(t, directory, "fragment.yml", "settings: {first: imported}\n")
+	input := []byte("configkit: {imports: [{path: fragment.yml}]}\n")
+	context := &FilesystemContext{BaseDir: directory, Root: directory}
+	for _, test := range []struct {
+		name   string
+		source func() Source
+	}{
+		{name: "bytes URI label", source: func() Source { return Bytes("s3://bucket/main.yml", input) }},
+		{name: "reader URI label", source: func() Source { return Reader("https://example.invalid/main.yml", strings.NewReader(string(input))) }},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			result, err := testLoad[importTestConfig](test.source(), Options[importTestConfig]{Imports: true, Filesystem: context})
+			if err != nil || result.Config.Settings.First != "imported" {
+				t.Fatalf("explicit filesystem result = %#v, %v", result, err)
+			}
+		})
+	}
+	requireLoadCode(t, Bytes("memory.yml", input), Options[importTestConfig]{Imports: true}, CodeOptionsInvalid)
+	requireLoadCode(t, Bytes("memory.yml", input), Options[importTestConfig]{Imports: true, Filesystem: &FilesystemContext{BaseDir: "relative", Root: directory}}, CodeOptionsInvalid)
+	requireLoadCode(t, Bytes("memory.yml", input), Options[importTestConfig]{Imports: true, Filesystem: &FilesystemContext{BaseDir: directory, Root: t.TempDir()}}, CodeImportOutsideRoot)
+}
+
+func TestFileImportRootCanContainTheSelectedFileDirectory(t *testing.T) {
+	root := t.TempDir()
+	mainPath := writeImportFile(t, root, "configs/main.yml", "configkit: {imports: [{path: ../shared.yml}]}\n")
+	writeImportFile(t, root, "shared.yml", "settings: {root: shared}\n")
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{
+		Imports: true, Filesystem: &FilesystemContext{Root: root},
+	})
+	if err != nil || result.Config.Settings.Root != "shared" {
+		t.Fatalf("explicit-root result = %#v, %v", result, err)
+	}
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true, Filesystem: &FilesystemContext{BaseDir: filepath.Dir(mainPath), Root: root}}, CodeOptionsInvalid)
+}
+
+func TestImportedParseAndDecodeDiagnosticsKeepTheirSource(t *testing.T) {
+	t.Run("parse", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: broken.yml}]}\n")
+		writeImportFile(t, directory, "broken.yml", "settings: [\n")
+		loadError := requireAnyLoadError(t, File(mainPath), Options[importTestConfig]{Imports: true})
+		diagnostics := loadError.Diagnostics()
+		if diagnostics[0].Code != CodeYAMLInvalid || diagnostics[0].Primary == nil || diagnostics[0].Primary.SourceID != "source-2" || len(loadError.Sources()) != 2 {
+			t.Fatalf("parse failure = diagnostics %#v, sources %#v", diagnostics, loadError.Sources())
+		}
+	})
+
+	t.Run("decode", func(t *testing.T) {
+		directory := t.TempDir()
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: unknown.yml}]}\n")
+		writeImportFile(t, directory, "unknown.yml", "unknown: value\n")
+		loadError := requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeDecodeUnknownField)
+		diagnostic := loadError.Diagnostics()[0]
+		if diagnostic.Primary == nil || diagnostic.Primary.SourceID != "source-2" {
+			t.Fatalf("decode diagnostic = %#v", diagnostic)
+		}
+	})
+}
+
+func TestOptionalImportDoesNotSuppressUnsafeOrUnreadableTargets(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "outside.yml", "configkit: {imports: [{path: ../missing.yml, optional: true}]}\n")
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeImportOutsideRoot)
+
+	locked := writeImportFile(t, directory, "locked.yml", "settings: {root: locked}\n")
+	if err := os.Chmod(locked, 0); err != nil {
+		t.Skipf("cannot create unreadable fixture: %v", err)
+	}
+	defer func() { _ = os.Chmod(locked, 0o600) }()
+	if file, err := os.Open(locked); err == nil {
+		_ = file.Close()
+		t.Skip("filesystem does not enforce the unreadable-file fixture")
+	}
+	mainPath = writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: locked.yml, optional: true}]}\n")
+	requireLoadCode(t, File(mainPath), Options[importTestConfig]{Imports: true}, CodeSourcePermission)
+}
+
+func TestImportTraversalEnforcesPrivateBudgets(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: one.yml}, {path: two.yml}]}\n")
+	writeImportFile(t, directory, "one.yml", "settings: {first: one}\n")
+	writeImportFile(t, directory, "two.yml", "settings: {second: two}\n")
+	main := parseImportMain(t, mainPath)
+	for _, test := range []struct {
+		name   string
+		limits importLimits
+	}{
+		{name: "source count", limits: importLimits{depth: 8, sources: 2, bytes: maxTotalBytes, nodes: maxDocumentNodes}},
+		{name: "aggregate bytes", limits: importLimits{depth: 8, sources: 8, bytes: main.bytes + 1, nodes: maxDocumentNodes}},
+		{name: "aggregate nodes", limits: importLimits{depth: 8, sources: 8, bytes: maxTotalBytes, nodes: countInputNodes(main.document) + 1}},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			_, _, diagnostics := loadImportedDocuments(File(mainPath), nil, main, nil, test.limits)
+			if len(diagnostics) != 1 || diagnostics[0].Code != CodeImportLimitExceeded {
+				t.Fatalf("budget diagnostics = %#v", diagnostics)
+			}
+		})
+	}
+
+	writeImportFile(t, directory, "one.yml", "configkit: {imports: [{path: nested.yml}]}\n")
+	writeImportFile(t, directory, "nested.yml", "settings: {nested: nested}\n")
+	main = parseImportMain(t, mainPath)
+	_, _, diagnostics := loadImportedDocuments(File(mainPath), nil, main, nil, importLimits{depth: 1, sources: 8, bytes: maxTotalBytes, nodes: maxDocumentNodes})
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeImportLimitExceeded {
+		t.Fatalf("depth diagnostics = %#v", diagnostics)
+	}
+}
+
+func TestImportTraversalAcceptsExactPrivateBudgets(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: imported.yml}]}\n")
+	importedPath := writeImportFile(t, directory, "imported.yml", "settings: {first: imported}\n")
+	main := parseImportMain(t, mainPath)
+	imported := parseImportMain(t, importedPath)
+	data, err := os.ReadFile(importedPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	limits := importLimits{
+		depth:   1,
+		sources: 2,
+		bytes:   main.bytes + int64(len(data)),
+		nodes:   countInputNodes(main.document) + countInputNodes(imported.document),
+	}
+	composed, sources, diagnostics := loadImportedDocuments(File(mainPath), nil, main, nil, limits)
+	if len(diagnostics) != 0 || composed == nil || len(sources) != 2 {
+		t.Fatalf("exact-limit composition = (%#v, %#v, %#v)", composed, sources, diagnostics)
+	}
+}
+
+func writeImportFile(t *testing.T, root, relative, contents string) string {
+	t.Helper()
+	filename := filepath.Join(root, filepath.FromSlash(relative))
+	if err := os.MkdirAll(filepath.Dir(filename), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filename, []byte(contents), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	return filename
+}
+
+func canonicalTestPath(t *testing.T, filename string) string {
+	t.Helper()
+	canonical, err := canonicalExistingPath(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return canonical
+}
+
+func requireLoadCode(t *testing.T, source Source, options Options[importTestConfig], code Code) *LoadError {
+	t.Helper()
+	loadError := requireAnyLoadError(t, source, options)
+	diagnostics := loadError.Diagnostics()
+	if len(diagnostics) == 0 || diagnostics[0].Code != code {
+		t.Fatalf("diagnostics = %#v, want %s", diagnostics, code)
+	}
+	return loadError
+}
+
+func requireAnyLoadError(t *testing.T, source Source, options Options[importTestConfig]) *LoadError {
+	t.Helper()
+	result, err := testLoad[importTestConfig](source, options)
+	if result != nil || err == nil {
+		t.Fatalf("result, error = %#v, %v", result, err)
+	}
+	var loadError *LoadError
+	if !errors.As(err, &loadError) {
+		t.Fatalf("error type = %T", err)
+	}
+	return loadError
+}
+
+func parseImportMain(t *testing.T, filename string) parsedSource {
+	t.Helper()
+	parsed, diagnostics := parseSource(File(filename), "source-1", defaultParseLimits())
+	if len(diagnostics) != 0 {
+		t.Fatalf("parse diagnostics = %#v", diagnostics)
+	}
+	return parsed
+}

internal/engine/independence_test.go

@@ -0,0 +1,139 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"testing"
+)
+
+type independentText string
+
+func (value independentText) MarshalText() ([]byte, error) {
+	return []byte(value), nil
+}
+
+func (value *independentText) UnmarshalText(text []byte) error {
+	*value = independentText(text)
+	return nil
+}
+
+type independentConfig struct {
+	Labels map[string]string `yaml:"labels"`
+	Items  []string          `yaml:"items"`
+	Custom independentText   `yaml:"custom"`
+}
+
+func TestParallelLoadsShareRulesButNotMutableValues(t *testing.T) {
+	definition := Definition[independentConfig]{
+		Defaults: func() independentConfig {
+			return independentConfig{
+				Labels: map[string]string{"default": "kept"},
+				Items:  []string{"default"},
+				Custom: "default",
+			}
+		},
+	}
+
+	const count = 32
+	results := make([]*testResult[independentConfig], count)
+	errorsByIndex := make([]error, count)
+	var group sync.WaitGroup
+	for index := range count {
+		group.Add(1)
+		go func(index int) {
+			defer group.Done()
+			input := fmt.Sprintf("custom: value-%d\n", index)
+			results[index], errorsByIndex[index] = testLoad(Bytes("parallel.yml", []byte(input)), Options[independentConfig]{Definition: definition})
+		}(index)
+	}
+	group.Wait()
+
+	for index, err := range errorsByIndex {
+		if err != nil {
+			t.Fatalf("testLoad(%d) failed: %v", index, err)
+		}
+	}
+	results[0].Config.Labels["default"] = "mutated"
+	results[0].Config.Items[0] = "mutated"
+	results[0].Config.Custom = "mutated"
+	for index := 1; index < count; index++ {
+		if results[index].Config.Labels["default"] != "kept" || results[index].Config.Items[0] != "default" || results[index].Config.Custom != independentText(fmt.Sprintf("value-%d", index)) {
+			t.Fatalf("result %d shares mutable state: %#v", index, results[index].Config)
+		}
+	}
+	var effective bytes.Buffer
+	if err := results[0].WriteEffective(&effective); err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(effective.String(), "mutated") || !strings.Contains(effective.String(), "default: kept") || !strings.Contains(effective.String(), "value-0") {
+		t.Fatalf("frozen effective snapshot = %q", effective.String())
+	}
+}
+
+func TestLoadedConfigurationIsSeparateFromInspection(t *testing.T) {
+	type configuration struct {
+		Value string `yaml:"value"`
+	}
+
+	loaded, err := Load[configuration](Bytes("config.yml", []byte("value: original\n")), testSecretBinding())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if loaded.Inspection == nil {
+		t.Fatal("inspection is nil")
+	}
+
+	loaded.Config.Value = "mutated"
+	var effective bytes.Buffer
+	if err := loaded.Inspection.WriteEffective(&effective); err != nil {
+		t.Fatal(err)
+	}
+	if effective.String() != "value: original\n" {
+		t.Fatalf("inspection changed with configuration: %q", effective.String())
+	}
+}
+
+func TestConcurrentLoadsOfCopiedReaderSourceHaveOneClaim(t *testing.T) {
+	source := Reader("shared", strings.NewReader("value: one\n"))
+	copied := source
+	type config struct {
+		Value string `yaml:"value"`
+	}
+
+	start := make(chan struct{})
+	errorsFound := make(chan error, 2)
+	var group sync.WaitGroup
+	for _, candidate := range []Source{source, copied} {
+		group.Add(1)
+		go func(candidate Source) {
+			defer group.Done()
+			<-start
+			_, err := testLoad[config](candidate)
+			errorsFound <- err
+		}(candidate)
+	}
+	close(start)
+	group.Wait()
+	close(errorsFound)
+
+	successes, used := 0, 0
+	for err := range errorsFound {
+		if err == nil {
+			successes++
+			continue
+		}
+		var loadError *LoadError
+		if errors.As(err, &loadError) {
+			diagnostics := loadError.Diagnostics()
+			if len(diagnostics) == 1 && diagnostics[0].Code == CodeSourceReaderUsed {
+				used++
+			}
+		}
+	}
+	if successes != 1 || used != 1 {
+		t.Fatalf("successes=%d reader-used=%d", successes, used)
+	}
+}

internal/engine/load.go

@@ -0,0 +1,190 @@
+package engine
+
+import (
+	"os"
+	"reflect"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+// Definition contains reusable application rules for a configuration type.
+// Secret is a pure predicate that can add sensitivity to semantic paths.
+// Definitions should be treated as read-only after being shared.
+type Definition[T any] struct {
+	Defaults func() T
+	Resolve  func(*T, *Resolution) error
+	Validate func(*T, *Validation)
+	Version  *VersionRule
+	Secret   func(Path) bool
+}
+
+// Options contains the application definition and per-load input selections.
+// Imports enables explicit path and glob imports; Overlay selects one fixed overlay;
+// Overrides contains only values explicitly supplied by an application CLI.
+type Options[T any] struct {
+	Definition Definition[T]
+	Imports    bool
+	Overlay    string
+	Filesystem *FilesystemContext
+	Overrides  []Override
+}
+
+// FilesystemContext supplies filesystem roots for imports and overlays.
+type FilesystemContext struct {
+	BaseDir string
+	Root    string
+}
+
+// Override describes one explicitly supplied application override. Value uses
+// parser-neutral built-in scalars, nil, []any, or map[string]any; Flag is a safe
+// display name and must not contain a raw argument or value.
+type Override struct {
+	Path  Path
+	Value any
+	Flag  string
+}
+
+// Resolution exposes entry-state input provenance, surviving-input presence, and
+// audited application resolution changes. A resolver must not retain or
+// concurrently use the context.
+type Resolution struct {
+	state *resolutionState
+}
+
+// VersionRule declares the input path and application checker for a schema version.
+// At that path, string and decimal-integer input is supplied as Version.Text.
+type VersionRule struct {
+	Path  Path
+	Check func(Version, *Validation) error
+}
+
+// Version preserves the absent, null, and textual states of a schema-version input.
+// Text is the exact spelling of accepted string or decimal-integer input.
+type Version struct {
+	Present bool
+	Null    bool
+	Text    string
+}
+
+// Loaded is a short-lived generic carrier for a successful configuration load.
+// Inspection is frozen independently of Config and does not retain application values.
+type Loaded[T any] struct {
+	Config     T
+	Inspection *Inspection
+}
+
+// Inspection owns frozen load snapshots and detached query state.
+type Inspection struct {
+	metadata         Metadata
+	sources          []SourceInfo
+	diagnostics      []Diagnostic
+	baseline         *document.Node
+	input            *document.Node
+	inputOrigins     map[string]Origin
+	final            *document.Node
+	resolution       []resolutionSnapshot
+	applications     []historyApplication
+	secrets          map[string]bool
+	secretReferences map[string]string
+}
+
+// Metadata returns detached effective presence, origin, and history records.
+func (r *Inspection) Metadata() Metadata {
+	if r == nil {
+		return Metadata{}
+	}
+	return cloneMetadata(r.metadata)
+}
+
+// Sources returns a detached list of sources used by the load.
+func (r *Inspection) Sources() []SourceInfo {
+	if r == nil {
+		return nil
+	}
+	return cloneSourceInfos(r.sources)
+}
+
+// Diagnostics returns detached nonfatal diagnostics from the load.
+func (r *Inspection) Diagnostics() []Diagnostic {
+	if r == nil {
+		return nil
+	}
+	return cloneDiagnostics(r.diagnostics)
+}
+
+// Load parses and strictly decodes zero or one selected source, explicitly enabled
+// imports, and one selected overlay. It accepts at most one Options value and
+// returns no result when any error is reported.
+func Load[T any](source Source, secrets SecretBinding, supplied ...Options[T]) (*Loaded[T], error) {
+	return loadWithSecretLookup(source, secrets, os.LookupEnv, supplied...)
+}
+
+func loadWithSecretLookup[T any](source Source, secrets SecretBinding, lookup secretLookup, supplied ...Options[T]) (*Loaded[T], error) {
+	accumulator := diagnosticAccumulator{}
+	options, diagnostics := selectOptions(source, supplied)
+	accumulator.add(diagnostics...)
+	if len(diagnostics) != 0 {
+		return nil, accumulator.loadError()
+	}
+
+	input, diagnostics := assembleBaseInput(source, options)
+	accumulator.sources = input.sources
+	accumulator.add(diagnostics...)
+	if len(diagnostics) != 0 {
+		return nil, accumulator.loadError()
+	}
+	schema, schemaIssue := buildSchema(reflect.TypeFor[T](), secrets)
+	if schemaIssue != nil {
+		accumulator.add(diagnosticFromSchemaIssue(schemaIssue))
+		return nil, accumulator.loadError()
+	}
+	versionDiagnostics := checkVersion(options.Definition.Version, input.document)
+	accumulator.add(versionDiagnostics...)
+	if hasErrors(versionDiagnostics) {
+		return nil, accumulator.loadError()
+	}
+	input, diagnostics = applyInputLayers(source, options, input)
+	accumulator.sources = input.sources
+	accumulator.add(diagnostics...)
+	if len(diagnostics) != 0 {
+		return nil, accumulator.loadError()
+	}
+
+	decoded, diagnostics := decodeLoadInput(schema, options.Definition, input)
+	accumulator.add(diagnostics...)
+	if len(diagnostics) != 0 {
+		return nil, accumulator.loadError()
+	}
+	resolved, diagnostics := resolveLoadInput(schema, options.Definition, input, decoded)
+	accumulator.add(diagnostics...)
+	if hasErrors(diagnostics) {
+		return nil, accumulator.loadError()
+	}
+	if !historyNodesWithinLimit(decoded.baseline, decoded.final, resolved.final, resolved.applications, resolved.snapshots) {
+		accumulator.add(Diagnostic{Code: CodeExplainLimitExceeded, Severity: SeverityError, Message: "retained configuration history exceeds the node limit"})
+		return nil, accumulator.loadError()
+	}
+
+	// Detach resolver-borrowed values before reference mutation or validation.
+	configuration, ownershipIssue := detachLoadConfiguration(schema, resolved.configuration, cloneUnresolvedSecrets)
+	if ownershipIssue != nil {
+		accumulator.add(*ownershipIssue)
+		return nil, accumulator.loadError()
+	}
+	secretResolution := resolveSecretReferences(reflect.ValueOf(&configuration).Elem(), schema, input.document, lookup)
+	accumulator.add(secretResolution.diagnostics...)
+	if hasErrors(secretResolution.diagnostics) {
+		return nil, accumulator.loadError()
+	}
+	if options.Definition.Validate != nil {
+		diagnostics = runValidation(&configuration, options.Definition.Validate, schema, resolved.final, input.document, secretResolution.lookups)
+		accumulator.add(diagnostics...)
+		if hasErrors(diagnostics) {
+			return nil, accumulator.loadError()
+		}
+	}
+	resolved.configuration = configuration
+	// Publication detaches equal-valued validator replacements, preserving the
+	// validated secret state, then finalizes metadata and sensitivity.
+	return publishLoadResult(schema, options.Definition, resolved, secretResolution.references, &accumulator)
+}