Prepare ConfigKit v0.4.0

.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 +1,5 @@
 Please review `docs/development.md` for initial orientation in this repository
 and follow its task-specific reading guide.
+
+Review and follow `docs/policy/agents.md` before recommending, planning, or
+implementing any changes to this repository.

README.md

@@ -2,17 +2,20 @@
 
 An opinionated Go library for applications that use YAML configuration files.
 
+Linux is release-validated; macOS support is best-effort. See the
+[platform support policy](docs/policy/release.md#platform-support) for details.
+
 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 profile and check an application schema version. It
+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 profiles. Value explanation is available through
+CLI override records apply above overlays. Value explanation is available through
 detached structured records and deterministic redacted output.
 
 ```go

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

@@ -1,248 +1,57 @@
 package configkit
 
 import (
-	"cmp"
-	"fmt"
 	"io"
-	"slices"
-	"strconv"
-	"strings"
-	"unicode"
+
+	"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 {
-	diagnostics []Diagnostic
-	sources     []SourceInfo
-}
+type LoadError struct{ value *engine.LoadError }
 
 // Error implements error without rendering diagnostic messages or input values.
 func (e *LoadError) Error() string {
-	if e == nil {
+	if e == nil || e.value == 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)
+	return e.value.Error()
 }
 
 // Diagnostics returns a deep copy of the error's canonical diagnostics.
 func (e *LoadError) Diagnostics() []Diagnostic {
-	if e == nil {
+	if e == nil || e.value == nil {
 		return nil
 	}
-	return cloneDiagnostics(e.diagnostics)
+	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 {
+	if e == nil || e.value == nil {
 		return nil
 	}
-	return cloneSourceInfos(e.sources)
+	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 {
-	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
+	return engine.WriteDiagnostics(output, toEngineDiagnostics(diagnostics))
 }

doc.go

@@ -1,10 +1,9 @@
 // Package configkit provides deterministic, application-owned configuration
 // loading for Go programs.
 //
-// Load currently supports one file, byte, reader, or explicit no-input source with
-// strict YAML, typed defaults, schema-version checks, detached metadata, safe
-// diagnostics, recorded application resolution, read-only semantic validation, and
-// structured load errors. Composition, profiles, overrides, secrets, and effective
-// rendering are not available yet. The configuration contract is documented in
-// docs/config.md.
+// 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/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

@@ -20,7 +20,7 @@ The zero `Source` is invalid. Constructor argument failures are retained inside
 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 profile is limited
+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
@@ -33,7 +33,7 @@ truncated. Data returned together with a read error is not accepted as partial i
 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-profile loading. Its result is detached before
+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
@@ -43,7 +43,7 @@ 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 profile
+  → 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
@@ -57,9 +57,9 @@ 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 profile, and
+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 profiles,
+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.
@@ -93,7 +93,7 @@ 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, profile, and CLI ownership
+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`
@@ -109,11 +109,11 @@ successful result. Callback panics remain programming failures.
 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 profile origin; omitted paths have a default origin.
+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 profile definitions, including
-equal-valued input. Profile replacement removes displaced descendants from effective
+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.
 
@@ -125,21 +125,21 @@ documentation in [metadata.go](../metadata.go) defines enumeration and path-orde
 details.
 
 History is chronological: a path can have a synthetic default record, its exact base
-definition, a profile replacement, and a recorded resolution operation. A descendant
+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 a profile
-has a profile-layer composite origin with the lower contributing locations followed
-by the profile location; an empty mapping is still an explicit container even though
+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 profile, then synthetic CLI records in supplied order.
+selected overlay, then synthetic CLI records in supplied order.
 
 ### Secret classification and effective rendering
 
@@ -189,7 +189,7 @@ historical path. Its effective value and each chronological before/after value a
 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 profile, supplied CLI records, and audited net
+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
@@ -199,7 +199,7 @@ 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, profile, and CLI history preserves the policy-validated input representation,
+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
@@ -293,10 +293,13 @@ operation once before starting concurrent work. The selected path may itself be
 symlink; ConfigKit resolves it to an existing canonical directory before examining
 its immediate entries.
 
-The bootstrap enumerates at most 1,024 entries and sorts them by filename. Every
-entry must have an ASCII environment-variable name and be a regular, nonsymlink
-file. Metadata for all entries is validated before file content is read or process
-state is changed. Existing environment variables win, including variables whose
+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
@@ -326,6 +329,27 @@ receives the working configuration and a per-load `Resolution` context. The cont
 `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
@@ -412,41 +436,41 @@ traversal order. Traversal order never authorizes replacement. Composition clone
 the resulting tree and its ordered claim records rather than mutating or aliasing an
 input document.
 
-## Selected profiles
+## Selected overlays
 
-`Options.Profile` selects at most one overlay by name. Names must match
+`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 profile, and `profiles/default.yml` is never loaded implicitly.
-Every other name resolves only to `<configuration-root>/profiles/<name>.yml`, with
-no extension fallback, case normalization, inheritance, or profile stack. A selected
-missing profile is an error.
+`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 profile is a separately policy-validated YAML mapping. It is loaded after the
+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. Profile bytes, nodes, and source records count toward the same
+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 profile node | Result |
+| Existing lower node | Incoming overlay node | Result |
 | --- | --- | --- |
-| Absent | Value | Retain the profile value |
+| 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 a profile sequence replaces rather
+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 profile paths have profile origins, while recursively shared
+replacement. Surviving overlay paths have overlay origins, while recursively shared
 mapping containers retain their contributing locations.
 
-A profile may not contain `configkit` anywhere, contribute the configured schema
+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. Profiles cannot mask a
+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
@@ -459,8 +483,8 @@ 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 profile and before typed defaults/decoding, so
-the input precedence is application defaults < composed base < selected profile <
+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`.
 
@@ -482,7 +506,7 @@ configured schema-version path. Unknown fields and effective type mismatches rem
 ordinary strict-decoder errors.
 
 At most 1,024 records are accepted, and each record creates one synthetic CLI
-source after file/profile sources in supplied order. Override sources share the
+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
@@ -490,7 +514,7 @@ 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/profile
+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

docs/consumers/README.md

@@ -1,7 +1,7 @@
 # Consumer Adoption Guide
 
 ConfigKit removes parser setup, strict decoding, presence bookkeeping, import and
-profile traversal, precedence, provenance, secret lookup, and safe inspection from
+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.
@@ -34,7 +34,7 @@ features appear only when the application needs them:
 result, err := configkit.Load[Config](configkit.File(path), configkit.Options[Config]{
     Definition: rules,
     Imports:    useDeclaredImports,
-    Profile:    selectedConfigProfile,
+    Overlay:    selectedConfigOverlay,
     Overrides:  explicitlySetFlags,
 })
 if err != nil {
@@ -43,8 +43,8 @@ if err != nil {
 return start(result.Config)
 ```
 
-Simple consumers use neither imports nor profiles. A complex consumer can opt into
-both without redefining their syntax. ConfigKit profiles are configuration overlays;
+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.
 
@@ -56,6 +56,24 @@ validate keys and ranges and convert only at their runtime boundary. Neither sha
 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:
@@ -82,6 +100,16 @@ The examples preserve domain meaning while adopting one configuration convention
   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
@@ -95,7 +123,7 @@ 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/profile pipeline rules and artifact defaults | Narratio-shaped executable example and fixture |
+| 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 |

docs/development.md

@@ -8,6 +8,8 @@ public behavior.
 ## Initial orientation
 
 1. Inspect the working tree and preserve unrelated changes.
+   Agents must read and follow the [agent policy](policy/agents.md) before
+   recommending, planning, or implementing 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 the relevant implementation and behavioral tests before changing them.
@@ -30,6 +32,7 @@ Accepted decisions:
 - [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. Completed implementation
 and remediation plans are preserved in Git history at `cb5b435`; use current
@@ -46,8 +49,20 @@ 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
 
+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:
@@ -80,8 +95,10 @@ 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 separate [release checker](release.md#4-validate-the-source-candidate) adds
-two-toolchain, module-hygiene, race, and cross-build gates.
+The [release checker](release.md#4-validate-the-source-candidate) performs one
+minimum-toolchain race-suite run, vet, module hygiene, and Linux cross-builds.
+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
 
@@ -91,15 +108,15 @@ code changes. Use the component overview to find the corresponding implementatio
 
 | Task | Behavioral test owners | Focused command |
 | --- | --- | --- |
-| YAML syntax, diagnostics, parser limits | [Adapter tests](../internal/yaml/parse_test.go), [source translation](../parse_test.go) | `go test ./internal/yaml` and `go test . -run '^TestParseSource'` |
-| File/reader access, imports, globs, containment | [Sources](../source_test.go), [FIFO](../source_fifo_test.go), [imports](../imports_test.go), [globs](../glob_test.go) | `go test . -run 'Source\|Import\|Glob\|Filesystem\|Nonregular\|RegularFile'` |
-| Composition, profiles, CLI precedence | [Composition](../compose_test.go), [overlay](../overlay_test.go), [profiles](../profile_test.go), [overrides](../override_test.go) | `go test . -run 'Compose\|Overlay\|Profile\|Override'` |
-| Schema, defaults, projection, cloning | [Schema](../schema_test.go), [decoding](../decode_test.go), [projection](../projection_test.go) | `go test . -run 'Schema\|Decode\|Projection\|Clone\|Inline\|CompareDocument'` |
-| Lifecycle, resolution, validation, callback ownership | [Loading](../load_test.go), [resolution](../resolution_test.go), [validation](../validation_test.go), [ownership](../callback_ownership_test.go), [independence](../independence_test.go) | `go test . -run 'Load\|Resolution\|Validation\|Validator\|Hook\|Callback\|Parallel'` |
-| Paths, metadata, provenance | [Paths](../path_test.go), [metadata](../metadata_test.go), [provenance](../provenance_test.go) | `go test . -run 'Path\|Metadata\|Provenance\|Queries'` |
-| Secrets, bootstrap, redaction, explanation | [References](../secret_reference_test.go), [bootstrap](../secrets_test.go), [rendering](../render_test.go), [explanation](../explain_test.go) | `go test . -run 'Secret\|Bootstrap\|Effective\|Explain\|Explanation\|History\|Sensitivity'` |
+| 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) | `go test . -run '^(TestLocalDocumentationLinks\|TestDependencyImportBoundary)$'` |
+| 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'` |
 | Check-command behavior | [Shell regression](../release_check_test.go) | `go test . -run '^TestCheckScripts'` |
 
 ## Fuzz validation
@@ -108,7 +125,7 @@ Run the bounded fuzz targets independently from the repository root. These exact
 commands keep each campaign short and constrain concurrent workers:
 
 ```sh
-go test . -run='^$' -fuzz='^FuzzParsePath$' -fuzztime=30s -parallel=2
+go test ./internal/engine -run='^$' -fuzz='^FuzzParsePath$' -fuzztime=30s -parallel=2
 go test ./internal/yaml -run='^$' -fuzz='^FuzzParseDocument$' -fuzztime=30s -parallel=2
-go test . -run='^$' -fuzz='^FuzzCompositionAndOverlay$' -fuzztime=30s -parallel=2
+go test ./internal/engine -run='^$' -fuzz='^FuzzCompositionAndOverlay$' -fuzztime=30s -parallel=2
 ```

docs/internal/extraction.md

@@ -137,9 +137,11 @@ permission failures, explicit `conf.d` use, and entry/candidate budgets. This wo
 has no Narratio production equivalent; it uses the selected standard-library
 `path.Match` and bounded `File.ReadDir` adaptation rather than its flat loader.
 
-### Profiles and overlay
+### Upstream profiles and ConfigKit selected overlays
 
-Assigned to selected-profile overlay:
+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
@@ -153,19 +155,21 @@ Assigned to selected-profile overlay:
   `TestLoadPipelineProfilePairResolvesIndependentEffectivePipelines`.
 - Preserve: recursive mapping overlay, atomic scalar/sequence replacement,
   deterministic selection failures, source ownership, and independent results.
-- Adapt: load only the selected fixed profile path; lowercase `default` means no
-  overlay. ConfigKit permits null and cross-kind replacement and does not support
-  declared defaults, inheritance, arbitrary profile paths, or validating every
+- 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): `overlayDocuments`, `mergeOverlayMappings`,
-`loadProfileDocument`, and `profileDirectiveDiagnostics` adapt the assigned merge,
-selection, loading, and ownership mechanics. `TestOverlayDocumentsRecursesMappingsAndReplacesAtomicSubtrees`,
-`TestLoadAppliesSelectedProfileAfterBaseAndBeforeDefaults`, profile selection/error,
-directive/version, containment, and budget cases adapt the assigned tests. ConfigKit
+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 profile directive or version-path
-contribution, and counts the profile in aggregate budgets. Narratio's declared
+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.
 
@@ -196,7 +200,7 @@ 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/profile/resolution workflow. ConfigKit
+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

docs/internal/overview.md

@@ -1,89 +1,39 @@
 # Internal Component Overview
 
-ConfigKit exposes the root `configkit` package and keeps its document and YAML
-representations private. The implemented components and their owners are:
+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.
 
-- immutable semantic `Path` construction and strict JSON Pointer parsing;
-- detached effective presence/origin and chronological history queries in
-  `metadata.go`, with provenance and diagnostic record types;
-- canonical, control-safe diagnostic rendering and structured `LoadError` access;
-- opaque file, byte, reader, and no-input source construction in `source.go`,
-  with shared regular-file checks and bounded read mechanics in `source_file.go`;
-- a parser-independent ordered tree in `internal/document`, with root-private
-  semantic lookup, indexing, and value traversal in `document_walk.go`;
-- the sole upstream YAML integration in `internal/yaml`, which translates validated
-  input into that owned tree and exposes no parser types outside its boundary;
-  `parse.go` owns shared translation into detached, ordered public diagnostics;
-- a private strict composer in `compose.go` that joins only disjoint document-tree
-  definitions, retains ordered claims and composite mapping origins, reports every
-  conflicting location, and never aliases an input tree;
-- fixed selected-profile loading in `profile.go` and recursive, non-aliasing overlay
-  with displacement records in `overlay.go`; overlay records retain origins,
-  while value explanation uses separate history applications;
-- CLI override validation/preparation in `override.go`, parser-neutral values in
-  `override_value.go`, and synthetic-source application in `override_apply.go`,
-  sharing overlay, source, byte, node, and depth policies;
-- a per-operation private reflection descriptor graph in `schema.go` for supported
-  types, YAML field binding, inlining, secret tags, recursion, and semantic paths;
-- descriptor-driven canonical projection in `projection.go`, detached typed
-  cloning with explicit secret-state modes in `clone.go`, shared reflection and
-  cycle/limit state in `value_operation.go`, and configuration-value comparison
-  in `document_compare.go`; validation separately audits sensitivity and secrets;
-- strict schema-driven decoding over detached defaults in `decode.go`, including
-  mapping/sequence semantics, null and numeric policy, safe codec errors, presence,
-  baseline/final trees, and initial default/input origins;
-- public lifecycle coordination in `load.go`, option selection in `options.go`,
-  input assembly in `load_input.go`, typed phases/publication in `load_result.go`,
-  bounded canonical import DFS in `imports.go`, filesystem context/containment in
-  `filesystem.go`, directive parsing/restrictions in `directives.go`,
-  pattern-directed glob expansion in `glob.go`, schema-version checking and report
-  contexts in `validation.go`, and layered metadata/history assembly in
-  `load_metadata.go`;
-- recorded application defaulting and normalization in `resolution.go`, including
-  explicitness queries, helper verification, structural mutation audit, coalesced
-  intent, private before/after snapshots, and resolution metadata integration;
-- post-resolution schema-aware report collection and validator mutation detection in
-  `validation.go`, completing the public callback lifecycle after composed input;
-- opaque typed environment references and per-load name resolution in
-  `secret_reference.go`, including credential-free projection/cloning and private
-  validator-state auditing;
-- explicit bounded startup environment bootstrap and safe partial reporting in
-  `secrets.go`;
-- fixed-point tag/predicate/dependency sensitivity classification in `secret.go`;
-- canonical effective output in `render.go`, using frozen-snapshot redaction
-  shared with explanation in `snapshot.go`;
-- detached public explanation records and coordination in `explain.go`, immutable
-  input applications/replay and retained-node budgeting in `history.go`, shared
-  safe snapshot projection in `snapshot.go`, and deterministic human output in
-  `explain_render.go`; the only upstream dumper integration remains isolated in
-  `internal/yaml/write.go`;
-- a separate maintained `examples/consumers` package with four sanitized consumer
-  shapes, fixtures, domain validators, and runtime-boundary functions; and
-- an everyday single-toolchain check in `scripts/check.sh` and a stricter
-  source-candidate checker in `scripts/release-check.sh`, with local
-  documentation-link and public import-boundary gates owned by root-package tests.
+Implemented component owners:
 
-Dependency direction remains inward: the public lifecycle coordinates private
-source, document, schema, and inspection helpers. Semantic paths stay in the root
-package; `internal/document` owns only representation and cloning and never imports
-the root package. Only `internal/yaml` imports the upstream YAML package. Maintained
-consumer examples use the public package and standard library.
+- `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`.
 
-The [configuration contract](../config.md) owns implemented input, schema, decoding,
-loading lifecycle, path imports, composition, profile/CLI overlay, version checking,
-recorded resolution, typed secret references/bootstrap, semantic validation,
-metadata, secret classification, redacted effective rendering, historical
-explanation, and ownership behavior.
-The [consumer adoption guide](../consumers/README.md) owns current application-fit
-and migration guidance.
+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 source-extraction inventory records the application foundations used by the
-implementation:
-
-- [Extraction inventory](extraction.md)
-
-The [architecture policy](../policy/architecture.md) owns binding boundaries and
-invariants. The [deferred scope](../roadmap/deferred.md) records deliberate
-exclusions. See the
-[development guide](../development.md) for contributor orientation and validation
-and the [release procedure](../release.md) for source-candidate gates.
+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/policy/agents.md

@@ -0,0 +1,91 @@
+# Agent Policy
+
+**Base Policy Version:** 1.1
+
+**Last Updated**: 2026-09-23
+
+## Purpose
+
+Agents working in this repository must read and adhere to the following house 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.
+
+Simplify the mechanism, not the user's choices.
+
+**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, create a commit after completing each coherent 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. Do not commit after every intermediate edit or create empty commits.
+Complete the appropriate validation before committing. If work is incomplete or
+validation is blocked, report that state rather than presenting it as completed.
+
+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. Do not disturb unrelated
+   staged or unstaged work.
+4. Review `git diff --staged` and run appropriate checks for the change. Do not
+   repeat checks already passed for unchanged content merely to create a commit.
+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

@@ -71,11 +71,23 @@ network provider into the library.
 ## 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
@@ -94,7 +106,7 @@ 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.
 

docs/policy/documentation.md

@@ -1,8 +1,8 @@
 # Documentation Policy
 
-**Base Policy Version:** 1.0
+**Base Policy Version:** 1.1
 
-**Last Updated:** 2026-09-06
+**Last Updated:** 2026-09-23
 
 ## Purpose
 
@@ -59,6 +59,7 @@ handling, not secret values.
 | Product orientation | `README.md` | Current status, purpose, navigation, and a minimal working example |
 | 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 |
+| Agent rules | `docs/policy/agents.md` | Implementation discipline, proportionality, rules against inventing contracts, and local commit authorization; not application contracts or architecture |
 | 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 |

docs/policy/release.md

@@ -1,8 +1,8 @@
 # Release Policy
 
-**Base Policy Version:** 0.1.0
+**Base Policy Version:** 1.0
 
-**Last Updated:** 2026-09-07
+**Last Updated:** 2026-09-23
 
 ## Purpose
 
@@ -21,7 +21,8 @@ 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.
+local target-build validation. Post-publication consumer retrieval is optional,
+as documented under Policy Exceptions.
 
 The release procedure must define the module path, authoritative remote,
 supported Go versions and operating-system/architecture targets, prerequisite
@@ -35,6 +36,20 @@ 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.
 
+### Platform support
+
+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.
+
+The [release procedure](../release.md#release-identity-and-support) owns target
+architectures and required Linux checks. This support change applies to upcoming
+releases; historical release notes and their validation records remain unchanged.
+The v0.3.0 release note must explain the change in Compatibility, with version
+selection following this policy's existing compatibility rules.
+
 ## Release Model
 
 A release consists of:
@@ -60,6 +75,10 @@ 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 annotated tag completes the source-only release.
+Never wait for CI or use its status as a readiness or completion gate. Optional
+post-publication checks must not delay reporting success.
+
 ## Versioning And Compatibility
 
 Stable releases use Semantic Versioning in the form `vMAJOR.MINOR.PATCH`, with
@@ -118,38 +137,28 @@ current documentation or defer required documentation changes.
 
 ## Candidate Preparation And Validation
 
-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 provides one local release checker. Run it once against the final
+committed candidate using one maintained patch of the minimum supported Go line
+on Linux. It checks module hygiene, formatting and whitespace, the full offline
+suite with the race detector, static analysis, and CGO-disabled Linux amd64/arm64
+builds. Examples, documentation links, consumer fixtures, and package boundaries
+are covered by that suite, not separate repeated runs. Native package compilation
+is covered by the test run. A second toolchain is optional and non-gating.
 
-The required gates are:
+Commit the release note and associated changes before release validation. Record
+the exact validated commit; revalidate if the candidate changes. Do not require
+both pre-commit and post-commit full checker runs for unchanged content.
+Do not publish uncommitted or unvalidated content. Local check failures still
+block publication. Skipped test cases are reported, not separate human sign-off
+requirements.
 
-- 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.
-
-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.
-
-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.
+Compatibility review, release-note accuracy, removal of completed roadmaps, and
+review for unintended files, credentials, private data, and unrelated changes
+are ordinary preparation. The executing agent may perform them without routine
+human approval or separate manual evidence records. Ask the maintainer only for
+genuine unresolved decisions or missing authority. A clean existing checkout is
+sufficient; a dedicated clone is optional. Dependency and toolchain update
+research belongs to maintenance or relevant changes, not every release.
 
 ## Publication Guards
 
@@ -164,7 +173,8 @@ verify all of the following:
 - 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
+- release publication is authorized and the local automated gates succeeded for
+  that commit; and
 - no local or remote tag already uses the selected version.
 
 Create the version tag against the guarded commit and verify its target before
@@ -205,21 +215,36 @@ order:
 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;
+4. candidate preparation and commit;
+5. one local validation pass, exact candidate recording, and push;
 6. publication guards;
 7. exact tag and deliverable publication commands;
-8. authoritative remote and consumer-facing verification; and
+8. completion on successful tag push and optional post-publication checks; 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
+and optional consumer verification path. It must link to this policy instead of
 restating or redefining its requirements.
 
 ## Policy Exceptions
 
+Any exception to this policy must be explicitly documented in this section,
+including the repository constraint requiring it, its rationale, scope, and
+compensating controls. Customizing release mechanics must not silently weaken
+the policy's integrity, validation, documentation, verification, or immutability
+requirements.
+
+For ConfigKit's source-only releases, the maintainer accepts successful publication
+of the intended tag as sufficient completion evidence. This is an explicit
+exception to the shared standard's mandatory post-publication verification:
+authoritative tag read-back and fresh consumer retrieval are optional and
+non-gating. CI status and downstream retrieval availability must not delay release
+completion. Compensating controls are local validation of the exact candidate,
+automated pre-publication guards, matching remote main, verification of the local
+annotated tag target, explicit ref pushes, and immutable published versions.
+
 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
@@ -233,5 +258,5 @@ 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.
 
-Candidate selection, publication, and post-publication verification remain
-mandatory steps in the [release procedure](../release.md).
+Candidate selection and guarded publication remain mandatory; post-publication
+verification is optional in the [release procedure](../release.md).

docs/release.md

@@ -12,18 +12,24 @@ binary, container image, generated package, or separate registry publication.
 - Authoritative remote: `origin`, expected to fetch from
   `https://gitea.maximumdirect.net/eric/ConfigKit.git`
 - Tags: stable Semantic Versions such as `v0.1.0`; prerelease tags are not supported
-- Minimum Go language/toolchain line: Go 1.25, tested with a supported patched
-  Go 1.25 toolchain and one newer supported toolchain
-- Build targets: Linux and macOS on amd64 and arm64
+- Minimum Go language/toolchain line: Go 1.25, release-validated with one maintained
+  patch of that line; newer-toolchain testing is optional and non-gating
+- Release-gated build targets: Linux on amd64 and arm64
+- Best-effort targets: macOS on amd64 and arm64, under the
+  [platform support policy](policy/release.md#platform-support)
 
-The automated checker cross-builds all four targets. Before release, the maintainer
-must also obtain native test, race, symlink, and permission-fixture evidence on Linux
-and macOS; cross-compilation is not native execution evidence.
+The local Linux checker includes native race tests and CGO-disabled cross-builds.
+Its output reports skipped filesystem cases; no separate evidence record or
+human sign-off is required. Native macOS checks and Darwin cross-builds are
+optional and do not gate publication.
+
+CI is never a release gate. Do not wait for it, poll its status, or delay reporting
+completion because it is pending, unavailable, or failed.
 
 ## 1. Prepare access and tools
 
-The release maintainer owns this procedure. Work in a dedicated clone with Git, Bash 3.2 or newer,
-and two supported Go toolchains available. The checker supports the stock macOS
+The release maintainer owns this procedure. Use a clean checkout (a dedicated clone is optional) with Git, Bash 3.2 or newer,
+a maintained Go 1.25 patch, and the compiler needed for native race tests. The checker supports the stock macOS
 Bash; its filename enumeration is null-delimited, including names with whitespace. Configure private-host Git and Go module
 access through the normal credential manager before starting. Keep tokens, passwords,
 SSH material, and environment dumps outside the repository and command transcript.
@@ -34,23 +40,24 @@ git remote get-url origin
 git ls-remote origin HEAD
 ```
 
-The remote URL must equal the authoritative URL above. Select the latest supported
-patch in the Go 1.25 line and a newer supported toolchain. The values below are the
-toolchains used while this runbook was introduced; update them to supported patch
-releases during candidate preparation and record the actual versions in the release
-note or validation record.
+The remote URL must equal the authoritative URL above. Acquire the selected
+toolchain and dependencies explicitly. For example, with the maintained patch
+used when this procedure was simplified:
 
 ```sh
-export CONFIGKIT_BASELINE_TOOLCHAIN=go1.25.5
-export CONFIGKIT_NEWER_TOOLCHAIN=go1.26.7
+export CONFIGKIT_BASELINE_TOOLCHAIN=go1.25.14
 GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go version
-GOTOOLCHAIN="$CONFIGKIT_NEWER_TOOLCHAIN" go version
 GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go mod download
-GOTOOLCHAIN="$CONFIGKIT_NEWER_TOOLCHAIN" go mod download
 ```
 
-Those commands explicitly acquire toolchains and dependencies. The checker itself
-sets `GOPROXY=off` and fails if its required cache is incomplete.
+Keep toolchains maintained, but do not require latest-version discovery for each
+release. The checker sets `GOPROXY=off` and fails if the cache is incomplete.
+Toolchain and YAML-dependency update research belongs to periodic maintenance or
+relevant dependency changes. No renewed approval of an unchanged pin is required.
+
+Use Bash with `set -euo pipefail` for the command blocks below so any failed gate
+stops the sequence. Publication requires user authorization; the agent policy's
+local-commit authorization is not permission to push or release.
 
 ## 2. Select the version and review compatibility
 
@@ -60,7 +67,7 @@ For the first release, review the whole public surface and current contracts.
 ```sh
 release_version=v0.1.0
 printf '%s\n' "$release_version" | grep -Eq '^v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$'
-git show-ref --verify --quiet "refs/tags/$release_version" && exit 1 || :
+if git show-ref --verify --quiet "refs/tags/$release_version"; then exit 1; fi
 if git ls-remote --exit-code --tags origin "refs/tags/$release_version" >/dev/null; then
   printf 'remote tag already exists: %s\n' "$release_version" >&2
   exit 1
@@ -76,16 +83,9 @@ intentional incompatible minor-release change must be explained with consumer ac
 patch releases must remain compatible within their minor line. Review the maintained
 consumer examples and the migration guide even when signatures did not change.
 
-Reassess `go.yaml.in/yaml/v4` rather than using `@latest` implicitly:
-
-```sh
-go list -m -versions go.yaml.in/yaml/v4
-go list -m -json go.yaml.in/yaml/v4@latest
-```
-
-If changing the explicit pin, make that a reviewed dependency change and rerun the
-complete checker, especially parser policy, limits, diagnostics, and rendering tests.
-If retaining a prerelease pin, record that decision in Compatibility.
+When dependencies change, review parser behavior and migration impact as part of
+that change. Keep Compatibility accurate about the dependency pin, but do not
+perform an external version survey for every patch release.
 
 ## 3. Write the release note
 
@@ -97,55 +97,46 @@ release note until there is a real candidate and reviewed content.
 
 ## 4. Validate the source candidate
 
-Run the complete checker from the repository root after dependencies have been
-acquired. It validates module manifests in a disposable copy, both supported Go
-toolchains, offline default tests, the native race detector, vet, native builds,
-CGO-disabled cross-builds, formatting and whitespace (including untracked files),
-examples, package isolation, and local documentation links.
+Before release validation, finish compatibility review, inspect the diff and file
+list for unintended content or credentials, retire completed roadmaps, repair
+links, and review the release note. These are ordinary preparation tasks the
+executing agent may perform, not separate human approvals or evidence records.
+Ask the maintainer only for an unresolved product decision or missing authority.
+
+Commit the candidate, staging only its intended changes, then run the checker
+once against that clean commit. Do not run both everyday and release checkers to
+repeat the same gates.
 
 ```sh
-./scripts/release-check.sh
-```
-
-`go vet` is the repository's static-analysis baseline. No additional linter is
-claimed. Links to current ConfigKit files and headings are strict. Recorded links to
-sibling consumer source are checked when those checkouts exist and are otherwise
-inapplicable in an isolated clone; their immutable revisions remain recorded in the
-extraction inventory.
-
-Complete these manual gates and record their evidence with the candidate:
-
-- The maintainer reviews compatibility and downstream migration impact against
-  `docs/config.md`, Go API comments, and the consumer guide.
-- The maintainer inspects `git status --short`, `git diff`, and the candidate file
-  list for credentials, private data, generated output, unintended files, and
-  unrelated changes.
-- The maintainer records successful native checker runs on Linux and macOS, including
-  filesystem capability tests. If either host is unavailable, release remains
-  blocked unless platform support is formally narrowed in current documentation.
-- The maintainer removes completed, obsolete documents under `docs/roadmap/`, repairs
-  inbound links, and reruns the checker. ADR rationale remains historical.
-- The maintainer reviews the exact version-matched release note for accuracy and
-  confirms it describes only deliverables that will actually be published.
-
-## 5. Commit, push, and record the candidate
-
-Commit all candidate source, contract, example, roadmap-retirement, and release-note
-changes, rerun the checker against that clean commit, then push only `main` and record
-the exact commit in Git metadata local to the clone:
-
-```sh
-git add .
+git status --short
+# Stage the specific files belonging to the candidate, then review:
+git diff --staged
 git commit --message "Prepare ConfigKit $release_version"
-./scripts/release-check.sh
 test -z "$(git status --porcelain=v1 --untracked-files=all)"
-git push origin HEAD:refs/heads/main
-git rev-parse HEAD | tee .git/configkit-release-candidate
-candidate_commit=$(cat .git/configkit-release-candidate)
+candidate_commit=$(git rev-parse HEAD)
+./scripts/release-check.sh
+test "$(git rev-parse HEAD)" = "$candidate_commit"
+test -z "$(git status --porcelain=v1 --untracked-files=all)"
+printf '%s\n' "$candidate_commit" > "$(git rev-parse --git-path configkit-release-candidate)"
 ```
 
-If review changes the source after this point, create and validate a new candidate;
-do not reuse the recorded commit.
+If the final candidate is already committed, omit the staging and commit commands;
+do not create an empty commit. The checker validates module manifests in a
+disposable copy, formatting, whitespace, the full offline suite once with the race
+detector and verbose skip reporting, vet once, and CGO-disabled Linux amd64/arm64
+builds. The suite includes examples, consumer fixtures, documentation links, and
+package boundaries; no separate reruns are required. No additional linter is
+claimed. Sibling-consumer links are checked when those checkouts exist and are
+otherwise inapplicable in an isolated checkout.
+
+A changed candidate requires validation again. Do not reuse a recorded candidate
+from an older revision. The record is written only after successful local checks.
+
+## 5. Prepare publication
+
+The following guarded sequence pushes only `main` and the selected tag. Local
+validation failures block it; CI does not. Keep the selected `release_version`
+from step 2 in the same shell. If starting a new shell, set it explicitly again.
 
 ## 6. Run publication guards
 
@@ -153,14 +144,12 @@ Immediately before tagging, fetch the authoritative branch and tags, restore the
 recorded variables if this is a new shell, and execute every guard:
 
 ```sh
-release_version=v0.1.0
-candidate_commit=$(cat .git/configkit-release-candidate)
+candidate_commit=$(cat "$(git rev-parse --git-path configkit-release-candidate)")
 git fetch --prune origin main
 git fetch --tags origin
 test "$(git branch --show-current)" = main
 test -z "$(git status --porcelain=v1 --untracked-files=all)"
 test "$(git rev-parse HEAD)" = "$candidate_commit"
-test "$(git rev-parse refs/remotes/origin/main)" = "$candidate_commit"
 test "$(git remote get-url origin)" = 'https://gitea.maximumdirect.net/eric/ConfigKit.git'
 printf '%s\n' "$release_version" | grep -Eq '^v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$'
 test -f "docs/releases/$release_version.md"
@@ -168,17 +157,22 @@ test "$(sed -n '1p' "docs/releases/$release_version.md")" = "# ConfigKit $releas
 for heading in Summary Compatibility Upgrade Changes; do
   grep -Fxq "## $heading" "docs/releases/$release_version.md"
 done
-git show-ref --verify --quiet "refs/tags/$release_version" && exit 1 || :
+if git show-ref --verify --quiet "refs/tags/$release_version"; then exit 1; fi
 if git ls-remote --exit-code --tags origin "refs/tags/$release_version" >/dev/null; then
   printf 'remote tag already exists: %s\n' "$release_version" >&2
   exit 1
 else
   test $? -eq 2
 fi
+git push origin HEAD:refs/heads/main
+git fetch origin main
+test "$(git rev-parse refs/remotes/origin/main)" = "$candidate_commit"
+test "$(git rev-parse HEAD)" = "$candidate_commit"
+test -z "$(git status --porcelain=v1 --untracked-files=all)"
 ```
 
-Confirm the recorded automated and manual approvals apply to exactly
-`$candidate_commit`. A successful older run is not evidence for a changed commit.
+The recorded local validation must apply to exactly `$candidate_commit`. No
+separate human sign-off, CI status, or manual evidence document is required.
 
 ## 7. Tag and publish the exact ref
 
@@ -191,15 +185,17 @@ test "$(git rev-list -n 1 "$release_version")" = "$candidate_commit"
 git push origin "refs/tags/$release_version:refs/tags/$release_version"
 ```
 
-The pushed tag completes the declared source-only publication. No Gitea release
-object or binary upload is required.
+A successful push of the intended tag completes the release. Report success now;
+do not wait for CI, module propagation, or any post-publication check. No Gitea
+release object or binary upload is required.
 
-## 8. Verify publication and clean consumer retrieval
+## 8. Optional post-publication checks
 
-Verify the authoritative tag and then retrieve that exact version into a new module
-without a local `replace` directive. Private-host credentials must already be
-configured. Use direct origin retrieval unless an explicitly approved internal Go
-proxy is the publication channel.
+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; their failure or unavailability does not delay release
+completion. Do not poll CI or wait for module propagation. Private-host credentials
+must already be configured. Example direct-origin verification:
 
 ```sh
 remote_tag_commit=$(git ls-remote origin "refs/tags/$release_version^{}" | awk '{print $1}')
@@ -226,13 +222,13 @@ EOF
 rm -rf -- "$consumer_dir"
 ```
 
-The final `go list` output must show the exact module path and `$release_version`.
-Record the result with the release evidence.
+If performed, the final `go list` output should show the exact module path and
+`$release_version`. Report optional verification separately from publication success.
 
 ## 9. Handle failures without replacement
 
-Before publication, fix the candidate, rerun every gate, commit, push, and record a
-new exact candidate. An unpublished local tag may be deleted only after verifying it
+Before publication, fix and commit the candidate, validate it, record the new
+exact candidate, and repeat the guarded publication sequence. An unpublished local tag may be deleted only after verifying it
 was never pushed or used by another release channel.
 
 After publication, never move, delete, or recreate the tag and never replace its

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/roadmap/deferred.md

@@ -15,7 +15,7 @@ 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 profile inheritance;
+- 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;

examples/consumers/consumers.go

@@ -4,6 +4,7 @@ package consumers
 
 import (
 	"math"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
@@ -28,14 +29,14 @@ type NarratioConfig struct {
 
 // LoadNarratio loads the maintained import fixture with Narratio-shaped rules.
 func LoadNarratio(path string) (*configkit.Result[NarratioConfig], error) {
-	return LoadNarratioProfile(path, "")
+	return LoadNarratioOverlay(path, "")
 }
 
-// LoadNarratioProfile selects a ConfigKit configuration overlay independently
+// LoadNarratioOverlay selects a ConfigKit configuration overlay independently
 // from the application's ModelProfile field.
-func LoadNarratioProfile(path, profile string) (*configkit.Result[NarratioConfig], error) {
+func LoadNarratioOverlay(path, overlay string) (*configkit.Result[NarratioConfig], error) {
 	return configkit.Load(configkit.File(path), configkit.Options[NarratioConfig]{
-		Imports: true, Profile: profile,
+		Imports: true, Overlay: overlay,
 		Definition: configkit.Definition[NarratioConfig]{
 			Defaults: func() NarratioConfig { return NarratioConfig{PollInterval: time.Minute} },
 			Resolve:  resolveNarratio,
@@ -146,6 +147,69 @@ func NotariusWindow(configuration NotariusConfig, binding int) (int, bool) {
 	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"`

examples/consumers/consumers_test.go

@@ -29,6 +29,12 @@ func Example_notarius() {
 	// 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")))
@@ -86,10 +92,13 @@ func TestMaintainedConsumerFixturesPreserveDomainOutcomes(t *testing.T) {
 	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)
 	}
-	profiled, err := consumers.LoadNarratioProfile(fixture("narratio", "pipeline.yml"), "testing")
-	if err != nil || profiled.Config.PollInterval.String() != "2m0s" ||
-		profiled.Config.ModelProfile != "concise" || len(profiled.Sources()) != 3 {
-		t.Fatalf("configuration/application profiles = %#v, %v", profiled, err)
+	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"))
@@ -194,7 +203,7 @@ func TestMigrationFixturesFailWithStableCodesAndPaths(t *testing.T) {
 			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-profile") {
+			if strings.Contains(diagnostics[0].Message, "wrong-before-overlay") {
 				t.Fatalf("diagnostic exposed raw parser input: %#v", diagnostics[0])
 			}
 		})
@@ -240,12 +249,89 @@ func TestWeatherLoadedAndConstructedRulesAgreeWithoutMutation(t *testing.T) {
 	}
 }
 
+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() {

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

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)
+	}
+}

import_boundary_test.go

@@ -41,6 +41,15 @@ func TestDependencyImportBoundary(t *testing.T) {
 			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
 	})

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/engine/callback_ownership_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "testing"
 
@@ -30,11 +30,11 @@ func TestCallbackAssignmentsAreDetachedAcrossLoads(t *testing.T) {
 			}
 			calls := 0
 			lookup := func(string) (string, bool) { calls++; return "credential", true }
-			first, err := loadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
+			first, err := testLoadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
 			if err != nil {
 				t.Fatal(err)
 			}
-			second, err := loadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
+			second, err := testLoadWithSecretLookup(NoSource(), lookup, Options[cfg]{Definition: definition})
 			if err != nil {
 				t.Fatal(err)
 			}

internal/engine/clone.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"encoding"
@@ -128,11 +128,11 @@ func (o *valueOperation) clone(value reflect.Value, descriptor *typeDescriptor,
 		return result, nil
 	case descriptorSecret:
 		result := reflect.New(value.Type()).Elem()
-		reference := value.Interface().(Secret)
+		reference := o.schema.secrets.Read(value)
 		if o.cloneMode == cloneValidatedSecrets {
 			result.Set(value)
-		} else if reference.specified {
-			result.Set(reflect.ValueOf(SecretEnv(reference.EnvName())))
+		} else if reference.Specified {
+			result.Set(o.schema.secrets.Make(SecretState{Name: reference.Name, Specified: true}))
 		}
 		return result, nil
 	case descriptorText:

internal/engine/compose.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 

internal/engine/compose_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"reflect"

internal/engine/composition_fuzz_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"

internal/engine/decode.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"encoding"
@@ -179,7 +179,7 @@ func decodeValue(node *document.Node, base reflect.Value, descriptor *typeDescri
 		if node.Kind != document.String {
 			return typeMismatch(path, node, "secret environment name")
 		}
-		return reflect.ValueOf(SecretEnv(node.Text)), nil
+		return schema.secrets.Make(SecretState{Name: node.Text, Specified: true}), nil
 	case descriptorText:
 		if node.Kind != document.String {
 			return typeMismatch(path, node, "text string")

internal/engine/decode_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"

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

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"

internal/engine/directives.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"path"
@@ -181,24 +181,24 @@ func nodeImportDiagnostic(code Code, path Path, message string, node *document.N
 	return Diagnostic{Code: code, Severity: SeverityError, Path: path, Message: message, Primary: &location}
 }
 
-func profileDirectiveDiagnostics(node *document.Node, current Path) []Diagnostic {
+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: CodeProfileDirective, Severity: SeverityError, Path: childPath,
-					Message: "profiles cannot contain configuration directives", Primary: &location,
+					Code: CodeOverlayDirective, Severity: SeverityError, Path: childPath,
+					Message: "overlays cannot contain configuration directives", Primary: &location,
 				}}
 			}
-			if diagnostics := profileDirectiveDiagnostics(entry.Value, childPath); len(diagnostics) != 0 {
+			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 := profileDirectiveDiagnostics(child, current.Index(index)); len(diagnostics) != 0 {
+			if diagnostics := overlayDirectiveDiagnostics(child, current.Index(index)); len(diagnostics) != 0 {
 				return diagnostics
 			}
 		}

internal/engine/document_compare.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"cmp"

internal/engine/document_walk.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 

internal/engine/explain.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 
@@ -36,7 +36,7 @@ type Explanation struct {
 
 // 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) {
+func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	if r == nil || r.final == nil || r.baseline == nil || !r.metadata.hasHistoricalPath(path) {
 		return Explanation{}, false
 	}

internal/engine/explain_render.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -14,7 +14,7 @@ var (
 
 // 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 {
+func (r *Inspection) WriteExplanation(output io.Writer, path Path) error {
 	if r == nil || output == nil {
 		return errExplanationUnavailable
 	}
@@ -38,7 +38,7 @@ func (r *Result[T]) WriteExplanation(output io.Writer, path Path) error {
 		rendered.WriteString("  - representation: ")
 		if change.Origin.Operation == ChangeDecoding {
 			rendered.WriteString("input to canonical typed\n")
-		} else if change.Origin.Layer == LayerBase || change.Origin.Layer == LayerProfile || change.Origin.Layer == LayerCLI {
+		} 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")

internal/engine/explain_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"
@@ -21,13 +21,13 @@ type explanationConcurrency struct {
 	} `yaml:"transcription"`
 }
 
-func TestExplainShowsDefaultBaseAndEffectiveProfileValue(t *testing.T) {
+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("profiles", "testing.yml"), "transcription:\n  concurrency: 1\n")
-	result, err := Load[explanationConcurrency](File(mainPath), Options[explanationConcurrency]{
-		Imports: true, Profile: "testing",
+	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
@@ -44,11 +44,17 @@ func TestExplainShowsDefaultBaseAndEffectiveProfileValue(t *testing.T) {
 	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 != LayerProfile ||
+	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 {
@@ -70,27 +76,27 @@ func TestExplainReplaysCLIResolutionContainersAndSafeHistoricalValues(t *testing
 	directory := t.TempDir()
 	mainPath := writeImportFile(t, directory, "config.yml", `concurrency: 8
 equal: same
-limit: wrong-before-profile
+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("profiles", "testing.yml"), `concurrency: 1
+	writeImportFile(t, directory, filepath.Join("overlays", "testing.yml"), `concurrency: 1
 equal: same
 limit: 7
-items: [profile]
-labels: {profile: retained}
+items: [overlay]
+labels: {overlay: retained}
 dynamic: selected
 `)
-	result, err := loadWithSecretLookup(File(mainPath), func(name string) (string, bool) {
+	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]{
-		Profile: "testing",
+		Overlay: "testing",
 		Overrides: []Override{
 			{Path: Keys("concurrency"), Value: 2, Flag: "--concurrency"},
 			{Path: Keys("equal"), Value: "same", Flag: "--equal"},
@@ -130,7 +136,7 @@ dynamic: selected
 	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, LayerProfile, LayerCLI, LayerResolution}) {
+	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" ||
@@ -149,7 +155,7 @@ dynamic: selected
 	}
 
 	limit, _ := result.Explain(Keys("limit"))
-	if got := explanationValues(limit); !reflect.DeepEqual(got, []string{"0\n", "wrong-before-profile\n", "7\n"}) {
+	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"))
@@ -182,7 +188,7 @@ dynamic: selected
 	}
 	labels, _ := result.Explain(Keys("labels"))
 	if len(labels.History) != 4 || !strings.Contains(labels.Effective.YAML, "default: retained") ||
-		!strings.Contains(labels.Effective.YAML, "profile: retained") || !strings.Contains(labels.Effective.YAML, "cli: 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 {
@@ -258,7 +264,7 @@ dynamic: selected
 	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-profile\n    source: layer=\"base\"\n    before (canonical typed)") {
+		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())
 	}
 }
@@ -285,7 +291,7 @@ func TestSecretsBootstrapLoadAndExplanationRemainSeparateAndSafe(t *testing.T) {
 	type config struct {
 		Credential Secret `yaml:"credential"`
 	}
-	result, err := Load[config](Bytes("config.yml", []byte("credential: "+name+"\n")))
+	result, err := testLoad[config](Bytes("config.yml", []byte("credential: "+name+"\n")))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -340,10 +346,10 @@ func TestExplanationReconcilesDefaultsAfterInputReplacement(t *testing.T) {
 				if cli {
 					opts.Overrides = []Override{{Path: Keys("m"), Value: map[string]any{"b": 2}, Flag: "--m"}}
 				} else {
-					writeImportFile(t, root, "profiles/p.yml", "m: {b: 2}\n")
-					opts.Profile = "p"
+					writeImportFile(t, root, "overlays/p.yml", "m: {b: 2}\n")
+					opts.Overlay = "p"
 				}
-				result, err := Load(File(main), opts)
+				result, err := testLoad(File(main), opts)
 				if err != nil {
 					t.Fatal(err)
 				}
@@ -380,11 +386,11 @@ func TestIntegerVersionInspectionRetainsInputAndReconcilesTypedValue(t *testing.
 		Defaults: func() config { return config{Version: "4"} },
 		Version:  rule,
 	}}
-	first, err := Load(Bytes("version.yml", []byte("version: 4\n")), options)
+	first, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), options)
 	if err != nil {
 		t.Fatal(err)
 	}
-	second, err := Load(Bytes("version.yml", []byte("version: 4\n")), options)
+	second, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), options)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -449,7 +455,7 @@ func TestSensitiveIntegerVersionStaysRedactedWithoutSecretLookup(t *testing.T) {
 		Version string `yaml:"version"`
 	}
 	lookups := 0
-	result, err := loadWithSecretLookup(Bytes("version.yml", []byte("version: 987654321\n")), func(string) (string, bool) {
+	result, err := testLoadWithSecretLookup(Bytes("version.yml", []byte("version: 987654321\n")), func(string) (string, bool) {
 		lookups++
 		return "CREDENTIAL_CANARY", true
 	}, Options[config]{Definition: Definition[config]{
@@ -476,7 +482,7 @@ func TestExplanationReplaysResolutionAdditionsAndOverlappingIntent(t *testing.T)
 	}
 	for _, overlap := range []bool{false, true} {
 		t.Run(fmt.Sprint(overlap), func(t *testing.T) {
-			result, err := Load(Bytes("base", []byte("m: {old: 1}\n")), Options[cfg]{Definition: Definition[cfg]{Resolve: func(c *cfg, r *Resolution) error {
+			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"))

internal/engine/filesystem.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"os"

internal/engine/glob.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"

internal/engine/glob_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"os"
@@ -26,7 +26,7 @@ items: {alpha: alpha}
 
 	var previous []SourceInfo
 	for run := 0; run < 2; run++ {
-		result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -68,7 +68,7 @@ items: {root: root}
 	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 := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -79,7 +79,7 @@ items: {root: root}
 	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 := Load[importTestConfig](File(plainPath), Options[importTestConfig]{Imports: true})
+	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)
 	}
@@ -116,7 +116,7 @@ func TestLoadGlobImportsRejectInvalidAndUnmatchedPatterns(t *testing.T) {
 		t.Fatal(err)
 	}
 	mainPath := writeGlobRoot(t, directory, "empty/*.yml", true)
-	result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: 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)
 	}
@@ -166,7 +166,7 @@ func TestLoadGlobImportsConfineSymlinkDirectories(t *testing.T) {
 			t.Skipf("symlinks unavailable: %v", err)
 		}
 		mainPath := writeGlobRoot(t, root, "linked/*.yml", false)
-		result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		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)
 		}
@@ -229,11 +229,11 @@ func TestGlobTraversalBoundsNonmatchesAndAcceptedCandidates(t *testing.T) {
 	}
 }
 
-func TestFilesystemContextIsValidatedWithoutImportsOrActiveProfile(t *testing.T) {
+func TestFilesystemContextIsValidatedWithoutImportsOrActiveOverlay(t *testing.T) {
 	directory := t.TempDir()
 	mainPath := writeImportFile(t, directory, "main.yml", "items: {root: root}\n")
-	result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{
-		Profile: "default", Filesystem: &FilesystemContext{Root: directory},
+	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)
@@ -242,20 +242,20 @@ func TestFilesystemContextIsValidatedWithoutImportsOrActiveProfile(t *testing.T)
 	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 = Load[importTestConfig](input, Options[importTestConfig]{Filesystem: &FilesystemContext{BaseDir: directory, Root: directory}})
+	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 := Load[importTestConfig](NoSource(), Options[importTestConfig]{Profile: "default"})
+	defaultsOnly, err := testLoad[importTestConfig](NoSource(), Options[importTestConfig]{Overlay: "default"})
 	if err != nil || defaultsOnly == nil {
-		t.Fatalf("default profile with NoSource = %#v, %v", defaultsOnly, err)
+		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 := Load[importTestConfig](File(selectedLink), Options[importTestConfig]{Filesystem: &FilesystemContext{Root: directory}})
+			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)
 			}

internal/engine/history.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"

internal/engine/imports.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"

internal/engine/imports_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -33,7 +33,7 @@ func TestLoadFormerDirectiveKeyIsApplicationData(t *testing.T) {
 	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 := Load[config](File(mainPath), Options[config]{Imports: imports})
+		result, err := testLoad[config](File(mainPath), Options[config]{Imports: imports})
 		if err != nil {
 			t.Fatalf("Imports=%v: %v", imports, err)
 		}
@@ -61,7 +61,7 @@ settings:
 	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 := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -89,6 +89,18 @@ settings:
 	}
 }
 
+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()
@@ -163,7 +175,7 @@ func TestLoadImportMissingContainmentAndRegularFileRules(t *testing.T) {
       optional: true
 settings: {root: retained}
 `)
-		result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		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)
 		}
@@ -253,7 +265,7 @@ func TestLoadImportsCanonicalSymlinksAndKeepsHardLinksDistinct(t *testing.T) {
 			t.Skipf("symlinks unavailable: %v", err)
 		}
 		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: link.yml}]}\n")
-		result, err := Load[importTestConfig](File(mainPath), Options[importTestConfig]{Imports: true})
+		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)
 		}
@@ -303,7 +315,7 @@ func TestLoadByteAndReaderImportsRequireExplicitFilesystemContext(t *testing.T)
 		{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 := Load[importTestConfig](test.source(), Options[importTestConfig]{Imports: true, Filesystem: context})
+			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)
 			}
@@ -318,7 +330,7 @@ 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 := Load[importTestConfig](File(mainPath), Options[importTestConfig]{
+	result, err := testLoad[importTestConfig](File(mainPath), Options[importTestConfig]{
 		Imports: true, Filesystem: &FilesystemContext{Root: root},
 	})
 	if err != nil || result.Config.Settings.Root != "shared" {
@@ -455,7 +467,7 @@ func requireLoadCode(t *testing.T, source Source, options Options[importTestConf
 
 func requireAnyLoadError(t *testing.T, source Source, options Options[importTestConfig]) *LoadError {
 	t.Helper()
-	result, err := Load[importTestConfig](source, options)
+	result, err := testLoad[importTestConfig](source, options)
 	if result != nil || err == nil {
 		t.Fatalf("result, error = %#v, %v", result, err)
 	}

internal/engine/independence_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"
@@ -38,7 +38,7 @@ func TestParallelLoadsShareRulesButNotMutableValues(t *testing.T) {
 	}
 
 	const count = 32
-	results := make([]*Result[independentConfig], count)
+	results := make([]*testResult[independentConfig], count)
 	errorsByIndex := make([]error, count)
 	var group sync.WaitGroup
 	for index := range count {
@@ -46,14 +46,14 @@ func TestParallelLoadsShareRulesButNotMutableValues(t *testing.T) {
 		go func(index int) {
 			defer group.Done()
 			input := fmt.Sprintf("custom: value-%d\n", index)
-			results[index], errorsByIndex[index] = Load(Bytes("parallel.yml", []byte(input)), Options[independentConfig]{Definition: definition})
+			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("Load(%d) failed: %v", index, err)
+			t.Fatalf("testLoad(%d) failed: %v", index, err)
 		}
 	}
 	results[0].Config.Labels["default"] = "mutated"
@@ -73,6 +73,29 @@ func TestParallelLoadsShareRulesButNotMutableValues(t *testing.T) {
 	}
 }
 
+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
@@ -88,7 +111,7 @@ func TestConcurrentLoadsOfCopiedReaderSourceHaveOneClaim(t *testing.T) {
 		go func(candidate Source) {
 			defer group.Done()
 			<-start
-			_, err := Load[config](candidate)
+			_, err := testLoad[config](candidate)
 			errorsFound <- err
 		}(candidate)
 	}

internal/engine/load.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"os"
@@ -19,17 +19,17 @@ type Definition[T any] struct {
 }
 
 // Options contains the application definition and per-load input selections.
-// Imports enables explicit path and glob imports; Profile selects one fixed profile
-// overlay; Overrides contains only values explicitly supplied by an application CLI.
+// 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
-	Profile    string
+	Overlay    string
 	Filesystem *FilesystemContext
 	Overrides  []Override
 }
 
-// FilesystemContext supplies filesystem roots for imports and profiles.
+// FilesystemContext supplies filesystem roots for imports and overlays.
 type FilesystemContext struct {
 	BaseDir string
 	Root    string
@@ -44,8 +44,9 @@ type Override struct {
 	Flag  string
 }
 
-// Resolution exposes surviving-input presence and records audited application
-// resolution changes. A resolver must not retain or concurrently use the context.
+// 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
 }
@@ -65,10 +66,15 @@ type Version struct {
 	Text    string
 }
 
-// Result is a successful independently owned configuration load.
-type Result[T any] struct {
-	Config T
+// 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
@@ -83,7 +89,7 @@ type Result[T any] struct {
 }
 
 // Metadata returns detached effective presence, origin, and history records.
-func (r *Result[T]) Metadata() Metadata {
+func (r *Inspection) Metadata() Metadata {
 	if r == nil {
 		return Metadata{}
 	}
@@ -91,7 +97,7 @@ func (r *Result[T]) Metadata() Metadata {
 }
 
 // Sources returns a detached list of sources used by the load.
-func (r *Result[T]) Sources() []SourceInfo {
+func (r *Inspection) Sources() []SourceInfo {
 	if r == nil {
 		return nil
 	}
@@ -99,7 +105,7 @@ func (r *Result[T]) Sources() []SourceInfo {
 }
 
 // Diagnostics returns detached nonfatal diagnostics from the load.
-func (r *Result[T]) Diagnostics() []Diagnostic {
+func (r *Inspection) Diagnostics() []Diagnostic {
 	if r == nil {
 		return nil
 	}
@@ -107,13 +113,13 @@ func (r *Result[T]) Diagnostics() []Diagnostic {
 }
 
 // Load parses and strictly decodes zero or one selected source, explicitly enabled
-// imports, and one selected profile. It accepts at most one Options value and
+// 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, supplied ...Options[T]) (*Result[T], error) {
-	return loadWithSecretLookup(source, os.LookupEnv, supplied...)
+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, lookup secretLookup, supplied ...Options[T]) (*Result[T], error) {
+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...)
@@ -127,7 +133,7 @@ func loadWithSecretLookup[T any](source Source, lookup secretLookup, supplied ..
 	if len(diagnostics) != 0 {
 		return nil, accumulator.loadError()
 	}
-	schema, schemaIssue := buildSchema(reflect.TypeFor[T]())
+	schema, schemaIssue := buildSchema(reflect.TypeFor[T](), secrets)
 	if schemaIssue != nil {
 		accumulator.add(diagnosticFromSchemaIssue(schemaIssue))
 		return nil, accumulator.loadError()

internal/engine/load_input.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 
@@ -25,7 +25,7 @@ func assembleBaseInput[T any](source Source, options Options[T]) (assembledInput
 		input.document = input.composition.root
 	} else {
 		input.sources = sourceInfos(parsed.source)
-		if options.Filesystem != nil && !activeProfile(options.Profile) {
+		if options.Filesystem != nil && !activeOverlay(options.Overlay) {
 			if diagnostic := validateFilesystemContext(source, options.Filesystem, parsed); diagnostic != nil {
 				return input, []Diagnostic{*diagnostic}
 			}
@@ -40,17 +40,17 @@ func assembleBaseInput[T any](source Source, options Options[T]) (assembledInput
 }
 
 func applyInputLayers[T any](source Source, options Options[T], input assembledInput) (assembledInput, []Diagnostic) {
-	if !activeProfile(options.Profile) && len(options.Overrides) == 0 {
+	if !activeOverlay(options.Overlay) && len(options.Overrides) == 0 {
 		return input, nil
 	}
 	composition, diagnostics := compositionForInput(input)
 	if len(diagnostics) != 0 {
 		return input, diagnostics
 	}
-	if activeProfile(options.Profile) {
-		composition, input.sources, diagnostics = loadProfileDocument(
+	if activeOverlay(options.Overlay) {
+		composition, input.sources, diagnostics = loadSelectedOverlayDocument(
 			source, options.Filesystem, input.parsed, composition, input.sources,
-			options.Profile, options.Definition.Version, defaultImportLimits(),
+			options.Overlay, options.Definition.Version, defaultImportLimits(),
 		)
 		if len(diagnostics) != 0 {
 			return input, diagnostics
@@ -69,7 +69,7 @@ func applyInputLayers[T any](source Source, options Options[T], input assembledI
 	return input, nil
 }
 
-// compositionForInput initializes one handoff for profiles and CLI, including
+// compositionForInput initializes one handoff for overlays and CLI, including
 // defaults-only CLI input. Raw source bytes and mapping keys retain their budgets.
 func compositionForInput(input assembledInput) (*composedDocument, []Diagnostic) {
 	if input.composition != nil {

internal/engine/load_metadata.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"slices"
@@ -6,6 +6,47 @@ import (
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 )
 
+// resolutionInput is the immutable entry-state provenance available to a
+// resolution callback. It owns detached metadata and source records so later
+// resolution updates cannot change the entry view.
+type resolutionInput struct {
+	metadata Metadata
+	sources  map[string]SourceInfo
+}
+
+func newResolutionInput(metadata Metadata, final *document.Node, sources []SourceInfo) resolutionInput {
+	frozen := Metadata{
+		fields:         make(map[string]FieldInfo, len(metadata.fields)),
+		effectivePaths: effectivePathIndex(final),
+	}
+	for pointer, info := range metadata.fields {
+		frozen.fields[pointer] = cloneFieldInfo(info)
+	}
+	indexed := make(map[string]SourceInfo, len(sources))
+	for _, source := range sources {
+		if source.ID == "" {
+			panic("configkit: source identity is missing")
+		}
+		if _, exists := indexed[source.ID]; exists {
+			panic("configkit: source identity is duplicated")
+		}
+		indexed[source.ID] = cloneSourceInfo(source)
+	}
+	return resolutionInput{metadata: frozen, sources: indexed}
+}
+
+func (input resolutionInput) lookup(path Path) (FieldInfo, bool) {
+	return input.metadata.Lookup(path)
+}
+
+func (input resolutionInput) source(id string) (SourceInfo, bool) {
+	source, ok := input.sources[id]
+	if !ok {
+		return SourceInfo{}, false
+	}
+	return cloneSourceInfo(source), true
+}
+
 func metadataFromDecoded(decoded decodedConfiguration) Metadata {
 	metadata := Metadata{
 		fields:  make(map[string]FieldInfo),

internal/engine/load_result.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"reflect"
@@ -51,7 +51,8 @@ func resolveLoadInput[T any](schema *schemaDescriptor, definition Definition[T],
 	final := decoded.final
 	var resolutionSnapshots []resolutionSnapshot
 	if definition.Resolve != nil {
-		resolved := runResolution(&configuration, definition.Resolve, schema, decoded, input.document)
+		entry := newResolutionInput(metadata, decoded.final, input.sources)
+		resolved := runResolution(&configuration, definition.Resolve, schema, decoded, input.document, entry)
 		diagnostics = append(diagnostics, resolved.diagnostics...)
 		if hasErrors(resolved.diagnostics) {
 			return resolvedLoad[T]{}, diagnostics
@@ -79,7 +80,7 @@ func detachLoadConfiguration[T any](schema *schemaDescriptor, configuration T, m
 	return detached.Interface().(T), nil
 }
 
-func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T], resolved resolvedLoad[T], references map[string]string, accumulator *diagnosticAccumulator) (*Result[T], error) {
+func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T], resolved resolvedLoad[T], references map[string]string, accumulator *diagnosticAccumulator) (*Loaded[T], error) {
 	// A read-only validator can replace a value with an equal borrowed object.
 	// Detach without re-reading the environment or discarding validated state.
 	configuration, issue := detachLoadConfiguration(schema, resolved.configuration, cloneValidatedSecrets)
@@ -91,8 +92,7 @@ func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T]
 	final, applications, resolutionSnapshots := resolved.final, resolved.applications, resolved.snapshots
 	finalizeMetadataPaths(&metadata, final, applications, decoded.baseline, decoded.final)
 	secrets := classifySecretPaths(schema, definition.Secret, metadata, final, applications, decoded.baseline, decoded.final)
-	return &Result[T]{
-		Config:           configuration,
+	inspection := &Inspection{
 		metadata:         metadata,
 		sources:          cloneSourceInfos(accumulator.sources),
 		diagnostics:      canonicalDiagnostics(accumulator.diagnostics),
@@ -104,7 +104,8 @@ func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T]
 		applications:     applications,
 		secrets:          secrets,
 		secretReferences: cloneSecretReferences(references),
-	}, nil
+	}
+	return &Loaded[T]{Config: configuration, Inspection: inspection}, nil
 }
 
 func diagnosticFromSchemaIssue(issue *schemaIssue) Diagnostic {

internal/engine/load_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -38,7 +38,7 @@ func TestLoadSingleSourceKindsAndDefaultsOnly(t *testing.T) {
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			var defaultsCalls atomic.Int32
-			result, err := Load(test.source(), Options[config]{Definition: Definition[config]{
+			result, err := testLoad(test.source(), Options[config]{Definition: Definition[config]{
 				Defaults: func() config {
 					defaultsCalls.Add(1)
 					return config{Name: "default"}
@@ -92,7 +92,7 @@ func TestLoadVersionStatesWarningsAndSafeFailures(t *testing.T) {
 				validation.Warning(versionPath, "review schema compatibility", Keys("missing_related"))
 				return nil
 			}}
-			result, err := Load(test.source, Options[config]{Definition: Definition[config]{Version: rule}})
+			result, err := testLoad(test.source, Options[config]{Definition: Definition[config]{Version: rule}})
 			if test.wantErr != "" {
 				if result != nil || err == nil {
 					t.Fatalf("result, err = %#v, %v", result, err)
@@ -144,21 +144,21 @@ func TestLoadDecodesIntegerVersionOnlyAtConfiguredStringPath(t *testing.T) {
 		load   func(Source, *VersionRule) (string, error)
 	}{
 		{name: "integer into string", source: "version: 4\n", load: func(source Source, rule *VersionRule) (string, error) {
-			result, err := Load(source, Options[stringConfig]{Definition: Definition[stringConfig]{Version: rule}})
+			result, err := testLoad(source, Options[stringConfig]{Definition: Definition[stringConfig]{Version: rule}})
 			if err != nil {
 				return "", err
 			}
 			return result.Config.Version, nil
 		}},
 		{name: "string into string", source: "version: \"4\"\n", load: func(source Source, rule *VersionRule) (string, error) {
-			result, err := Load(source, Options[stringConfig]{Definition: Definition[stringConfig]{Version: rule}})
+			result, err := testLoad(source, Options[stringConfig]{Definition: Definition[stringConfig]{Version: rule}})
 			if err != nil {
 				return "", err
 			}
 			return result.Config.Version, nil
 		}},
 		{name: "integer into pointer", source: "version: 4\n", load: func(source Source, rule *VersionRule) (string, error) {
-			result, err := Load(source, Options[pointerConfig]{Definition: Definition[pointerConfig]{Version: rule}})
+			result, err := testLoad(source, Options[pointerConfig]{Definition: Definition[pointerConfig]{Version: rule}})
 			if err != nil {
 				return "", err
 			}
@@ -168,7 +168,7 @@ func TestLoadDecodesIntegerVersionOnlyAtConfiguredStringPath(t *testing.T) {
 			return *result.Config.Version, nil
 		}},
 		{name: "string into pointer", source: "version: \"4\"\n", load: func(source Source, rule *VersionRule) (string, error) {
-			result, err := Load(source, Options[pointerConfig]{Definition: Definition[pointerConfig]{Version: rule}})
+			result, err := testLoad(source, Options[pointerConfig]{Definition: Definition[pointerConfig]{Version: rule}})
 			if err != nil {
 				return "", err
 			}
@@ -194,7 +194,7 @@ func TestLoadDecodesIntegerVersionOnlyAtConfiguredStringPath(t *testing.T) {
 		})
 	}
 
-	if result, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[stringConfig]{}); result != nil {
+	if result, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[stringConfig]{}); result != nil {
 		t.Fatalf("load without rule = %#v, %v", result, err)
 	} else {
 		var loadError *LoadError
@@ -207,7 +207,7 @@ func TestLoadDecodesIntegerVersionOnlyAtConfiguredStringPath(t *testing.T) {
 		Label   string `yaml:"label"`
 	}
 	rule := &VersionRule{Path: versionPath, Check: func(Version, *Validation) error { return nil }}
-	if result, err := Load(Bytes("version.yml", []byte("version: 4\nlabel: 5\n")), Options[unrelatedConfig]{Definition: Definition[unrelatedConfig]{Version: rule}}); result != nil {
+	if result, err := testLoad(Bytes("version.yml", []byte("version: 4\nlabel: 5\n")), Options[unrelatedConfig]{Definition: Definition[unrelatedConfig]{Version: rule}}); result != nil {
 		t.Fatalf("unrelated coercion = %#v, %v", result, err)
 	} else {
 		var loadError *LoadError
@@ -240,7 +240,7 @@ func TestLoadVersionScalarAndPathBoundaries(t *testing.T) {
 				checked = version
 				return nil
 			}}
-			result, err := Load(Bytes("version.yml", []byte("version: "+test.value+"\n")), Options[config]{Definition: Definition[config]{Version: rule}})
+			result, err := testLoad(Bytes("version.yml", []byte("version: "+test.value+"\n")), Options[config]{Definition: Definition[config]{Version: rule}})
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -266,7 +266,7 @@ func TestLoadVersionScalarAndPathBoundaries(t *testing.T) {
 				called = true
 				return nil
 			}}
-			result, err := Load(Bytes("version.yml", []byte("version: "+test.value+"\n")), Options[config]{Definition: Definition[config]{Version: rule}})
+			result, err := testLoad(Bytes("version.yml", []byte("version: "+test.value+"\n")), Options[config]{Definition: Definition[config]{Version: rule}})
 			if result != nil || called {
 				t.Fatalf("result = %#v, checker called = %v", result, called)
 			}
@@ -289,7 +289,7 @@ func TestLoadVersionScalarAndPathBoundaries(t *testing.T) {
 		}
 		return nil
 	}}
-	result, err := Load(Bytes("nested.yml", []byte("versions:\n  \"0\": 4\nsibling: quoted\n")), Options[nested]{Definition: Definition[nested]{Version: rule}})
+	result, err := testLoad(Bytes("nested.yml", []byte("versions:\n  \"0\": 4\nsibling: quoted\n")), Options[nested]{Definition: Definition[nested]{Version: rule}})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -299,7 +299,7 @@ func TestLoadVersionScalarAndPathBoundaries(t *testing.T) {
 	type sequenceConfig struct {
 		Versions []namedVersion `yaml:"versions"`
 	}
-	sequenceResult, err := Load(Bytes("sequence.yml", []byte("versions: [6]\n")), Options[sequenceConfig]{Definition: Definition[sequenceConfig]{Version: &VersionRule{Path: parsed, Check: func(Version, *Validation) error { return nil }}}})
+	sequenceResult, err := testLoad(Bytes("sequence.yml", []byte("versions: [6]\n")), Options[sequenceConfig]{Definition: Definition[sequenceConfig]{Version: &VersionRule{Path: parsed, Check: func(Version, *Validation) error { return nil }}}})
 	if err != nil || len(sequenceResult.Config.Versions) != 1 || sequenceResult.Config.Versions[0] != "6" {
 		t.Fatalf("sequence configuration = %#v, %v", sequenceResult, err)
 	}
@@ -311,13 +311,13 @@ func TestLoadVersionScalarAndPathBoundaries(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	escapedResult, err := Load(Bytes("escaped.yml", []byte("versions:\n  a/b: 9\n")), Options[escaped]{Definition: Definition[escaped]{Version: &VersionRule{Path: escapedPath, Check: func(Version, *Validation) error { return nil }}}})
+	escapedResult, err := testLoad(Bytes("escaped.yml", []byte("versions:\n  a/b: 9\n")), Options[escaped]{Definition: Definition[escaped]{Version: &VersionRule{Path: escapedPath, Check: func(Version, *Validation) error { return nil }}}})
 	if err != nil || escapedResult.Config.Versions["a/b"] != "9" {
 		t.Fatalf("escaped configuration = %#v, %v", escapedResult, err)
 	}
 
 	siblingRule := &VersionRule{Path: Keys("versions", "target"), Check: func(Version, *Validation) error { return nil }}
-	if result, err := Load(Bytes("sibling.yml", []byte("versions:\n  target: 4\n  other: 5\n")), Options[escaped]{Definition: Definition[escaped]{Version: siblingRule}}); result != nil {
+	if result, err := testLoad(Bytes("sibling.yml", []byte("versions:\n  target: 4\n  other: 5\n")), Options[escaped]{Definition: Definition[escaped]{Version: siblingRule}}); result != nil {
 		t.Fatalf("same-type sibling result = %#v, %v", result, err)
 	} else {
 		requireDiagnostic(t, err, CodeDecodeType, "/versions/other")
@@ -332,16 +332,16 @@ func TestLoadVersionDestinationTypesKeepOrdinaryDecoding(t *testing.T) {
 		type config struct {
 			Version int8 `yaml:"version"`
 		}
-		result, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+		result, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 		if err != nil || result.Config.Version != 4 {
 			t.Fatalf("result = %#v, %v", result, err)
 		}
-		result, err = Load(Bytes("version.yml", []byte("version: 999\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+		result, err = testLoad(Bytes("version.yml", []byte("version: 999\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 		if result != nil {
 			t.Fatalf("range result = %#v", result)
 		}
 		requireDiagnostic(t, err, CodeDecodeRange, "/version")
-		result, err = Load(Bytes("version.yml", []byte("version: \"4\"\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+		result, err = testLoad(Bytes("version.yml", []byte("version: \"4\"\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 		if result != nil {
 			t.Fatalf("quoted integer result = %#v", result)
 		}
@@ -352,11 +352,11 @@ func TestLoadVersionDestinationTypesKeepOrdinaryDecoding(t *testing.T) {
 		type config struct {
 			Version any `yaml:"version"`
 		}
-		result, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+		result, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 		if err != nil || result.Config.Version != int64(4) {
 			t.Fatalf("result = %#v, %v", result, err)
 		}
-		result, err = Load(Bytes("version.yml", []byte("version: 123456789012345678901234567890\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+		result, err = testLoad(Bytes("version.yml", []byte("version: 123456789012345678901234567890\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 		if result != nil {
 			t.Fatalf("range result = %#v", result)
 		}
@@ -371,21 +371,21 @@ func TestLoadVersionDestinationTypesKeepOrdinaryDecoding(t *testing.T) {
 			type config struct {
 				Version validatedText `yaml:"version"`
 			}
-			_, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+			_, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 			return err
 		}},
 		{name: "duration", load: func() error {
 			type config struct {
 				Version time.Duration `yaml:"version"`
 			}
-			_, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+			_, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 			return err
 		}},
 		{name: "secret", load: func() error {
 			type config struct {
 				Version Secret `yaml:"version"`
 			}
-			_, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
+			_, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{Version: &VersionRule{Path: Keys("version"), Check: check}}})
 			return err
 		}},
 	} {
@@ -409,7 +409,7 @@ func TestLoadVersionPolicyStopsLaterHooks(t *testing.T) {
 		validation.Error(Keys("version"), "unsupported configuration version")
 		return nil
 	}}
-	result, err := Load(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("version.yml", []byte("version: 4\n")), Options[config]{Definition: Definition[config]{
 		Defaults: func() config { defaultsCalled = true; return config{} },
 		Version:  rule,
 		Resolve:  func(*config, *Resolution) error { resolutionCalled = true; return nil },
@@ -440,7 +440,7 @@ func TestLoadVersionReportSuppressesReturnedErrorTextAndDefaults(t *testing.T) {
 		Name string `yaml:"name"`
 	}
 	var defaultsCalls atomic.Int32
-	result, err := Load(Bytes("version.yml", []byte("name: value\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("version.yml", []byte("name: value\n")), Options[config]{Definition: Definition[config]{
 		Defaults: func() config {
 			defaultsCalls.Add(1)
 			return config{Name: "default"}
@@ -474,7 +474,7 @@ func TestLoadMetadataReflectsDefaultsInputAndDetachedRecords(t *testing.T) {
 		Nested   nested            `yaml:"nested"`
 		Nullable map[string]string `yaml:"nullable"`
 	}
-	result, err := Load(Bytes("metadata.yml", []byte("nested: {set: configured}\nnullable: null\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("metadata.yml", []byte("nested: {set: configured}\nnullable: null\n")), Options[config]{Definition: Definition[config]{
 		Defaults: func() config {
 			return config{Nested: nested{Kept: "default", Set: "default"}, Nullable: map[string]string{"key": "value"}}
 		},
@@ -538,7 +538,7 @@ func TestLoadRejectsUnavailableOptionsAndDisabledDirectives(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			result, err := Load(test.source, test.options...)
+			result, err := testLoad(test.source, test.options...)
 			if result != nil || err == nil {
 				t.Fatalf("result, err = %#v, %v", result, err)
 			}
@@ -549,7 +549,7 @@ func TestLoadRejectsUnavailableOptionsAndDisabledDirectives(t *testing.T) {
 		})
 	}
 
-	result, err := Load[config](Bytes("directive.yml", []byte("nested:\n  configkit: {}\n")))
+	result, err := testLoad[config](Bytes("directive.yml", []byte("nested:\n  configkit: {}\n")))
 	if result != nil || err == nil {
 		t.Fatalf("result, err = %#v, %v", result, err)
 	}
@@ -577,9 +577,9 @@ func TestLoadReturnsNilForSourceSchemaAndDecodeFailures(t *testing.T) {
 		run  func() (any, error)
 		code Code
 	}{
-		{name: "source", run: func() (any, error) { return Load[validConfig](File(filepath.Join(t.TempDir(), "missing.yml"))) }, code: CodeSourceMissing},
-		{name: "schema", run: func() (any, error) { return Load[invalidSchema](Bytes("schema.yml", []byte("{}\n"))) }, code: CodeSchemaUnsupportedType},
-		{name: "decode", run: func() (any, error) { return Load[validConfig](Bytes("decode.yml", []byte("unknown: 1\n"))) }, code: CodeDecodeUnknownField},
+		{name: "source", run: func() (any, error) { return testLoad[validConfig](File(filepath.Join(t.TempDir(), "missing.yml"))) }, code: CodeSourceMissing},
+		{name: "schema", run: func() (any, error) { return testLoad[invalidSchema](Bytes("schema.yml", []byte("{}\n"))) }, code: CodeSchemaUnsupportedType},
+		{name: "decode", run: func() (any, error) { return testLoad[validConfig](Bytes("decode.yml", []byte("unknown: 1\n"))) }, code: CodeDecodeUnknownField},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {

internal/engine/metadata.go

@@ -0,0 +1,149 @@
+package engine
+
+import (
+	"sort"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+// Metadata provides detached effective presence/origin and chronological history
+// queries for a load. Its zero value contains no paths.
+type Metadata struct {
+	effectivePaths  map[string]Path
+	historicalPaths map[string][]Path
+	fields          map[string]FieldInfo
+	history         map[string][]Change
+}
+
+// Lookup returns information for an effective path. Unknown and invalid paths
+// return false.
+func (m Metadata) Lookup(path Path) (FieldInfo, bool) {
+	if !path.valid() || !matchesPathShape(path, m.effectivePaths[path.String()]) {
+		return FieldInfo{}, false
+	}
+	info, ok := m.fields[path.String()]
+	if !ok {
+		return FieldInfo{}, false
+	}
+	return cloneFieldInfo(info), true
+}
+
+// IsExplicit reports whether a surviving input contribution explicitly defined
+// path.
+func (m Metadata) IsExplicit(path Path) bool {
+	info, ok := m.Lookup(path)
+	return ok && info.Explicit
+}
+
+// History returns detached definition and resolution records for path. A record's
+// Path can be an ancestor when that container operation replaced or removed path.
+// Removed historical paths can have history even though Lookup returns false.
+// Unknown and invalid paths return nil.
+func (m Metadata) History(path Path) []Change {
+	if !m.hasHistoricalPath(path) {
+		return nil
+	}
+	history, ok := m.history[path.String()]
+	if !ok {
+		return nil
+	}
+	cloned := make([]Change, len(history))
+	for i, change := range history {
+		cloned[i] = cloneChange(change)
+	}
+	return cloned
+}
+
+// HistoricalPaths returns the paths observed during loading, including effective
+// paths and paths removed by overlays or recorded resolution. It includes default
+// paths and the root, but not paths that never existed. The zero Metadata returns
+// an empty slice.
+//
+// Paths are detached, unique by canonical JSON Pointer, and sorted by that
+// spelling. Like ParsePath results, numeric tokens are resolved contextually;
+// one pointer can identify a mapping key in an earlier layer and a sequence index
+// in a later one. Use History to inspect definitions and Lookup to check whether
+// a path remains effective. Enumeration exposes no configuration values and does
+// not perform another load or resolve secrets.
+func (m Metadata) HistoricalPaths() []Path {
+	pointers := make([]string, 0, len(m.historicalPaths))
+	for pointer := range m.historicalPaths {
+		pointers = append(pointers, pointer)
+	}
+	sort.Strings(pointers)
+	paths := make([]Path, 0, len(pointers))
+	for _, pointer := range pointers {
+		// The index contains only canonical pointers produced by Path.String.
+		path, _ := ParsePath(pointer)
+		paths = append(paths, path)
+	}
+	return paths
+}
+
+// Textual pointers are lookup keys, but explicit key/index kinds remain part of
+// the query. Candidate paths are constructed from actual document containers.
+func matchesPathShape(query, candidate Path) bool {
+	if !query.valid() || query.String() != candidate.String() || len(query.segments) != len(candidate.segments) {
+		return false
+	}
+	for i, segment := range query.segments {
+		actual := candidate.segments[i]
+		if actual.kind == pathSegmentIndex {
+			index, ok := schemaIndex(segment)
+			if !ok || index != actual.index {
+				return false
+			}
+		} else if segment.kind == pathSegmentIndex {
+			return false
+		}
+	}
+	return true
+}
+
+func (m Metadata) hasHistoricalPath(path Path) bool {
+	if !path.valid() {
+		return false
+	}
+	for _, candidate := range m.historicalPaths[path.String()] {
+		if matchesPathShape(path, candidate) {
+			return true
+		}
+	}
+	return false
+}
+
+func finalizeMetadataPaths(m *Metadata, final *document.Node, applications []historyApplication, earlier ...*document.Node) {
+	m.effectivePaths = effectivePathIndex(final)
+	m.historicalPaths = make(map[string][]Path)
+	add := func(path Path, _ *document.Node) {
+		pointer := path.String()
+		for _, prior := range m.historicalPaths[pointer] {
+			if matchesPathShape(path, prior) {
+				return
+			}
+		}
+		m.historicalPaths[pointer] = append(m.historicalPaths[pointer], path.clone())
+	}
+	walkDocument(final, Path{}, add)
+	for _, tree := range earlier {
+		walkDocument(tree, Path{}, add)
+	}
+	for _, application := range applications {
+		// Overrides have mapping-only prefixes; parsed tokens are keys in this layer.
+		prefix := Path{}
+		for _, segment := range application.path.segments {
+			prefix = prefix.Key(segment.key)
+		}
+		walkDocument(application.value, prefix, add)
+	}
+}
+
+// effectivePathIndex records document-derived paths with their contextual segment
+// kinds. Callers retain no aliases to the walked tree or its paths.
+func effectivePathIndex(final *document.Node) map[string]Path {
+	paths := make(map[string]Path)
+	walkDocument(final, Path{}, func(path Path, _ *document.Node) {
+		paths[path.String()] = path.clone()
+	})
+	return paths
+}

internal/engine/metadata_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"
@@ -8,7 +8,7 @@ import (
 
 func TestMetadataHistoricalPaths(t *testing.T) {
 	t.Parallel()
-	result, err := Load[map[string]any](Bytes("base", []byte("retired: {child: 1}\nshape: {'0': base}\n'a/b~': {'': 2}\n")), Options[map[string]any]{
+	result, err := testLoad[map[string]any](Bytes("base", []byte("retired: {child: 1}\nshape: {'0': base}\n'a/b~': {'': 2}\n")), Options[map[string]any]{
 		Overrides: []Override{
 			{Path: Keys("retired"), Value: nil, Flag: "--retired"},
 			{Path: Keys("shape"), Value: []any{"replacement"}, Flag: "--shape"},
@@ -60,8 +60,8 @@ func TestHistoricalPathsExposeHiddenBaseOwnershipWithoutResolvingBaseSecrets(t *
 			root := writeImportFile(t, dir, "main.yml", "configkit:\n  imports: [{path: first.yml}, {path: second.yml}]\ncredential: CONFIGKIT_HISTORY_UNUSED_PROD_KEY\n")
 			writeImportFile(t, dir, "first.yml", "definitions: {recap: {prompt: recap}}\n")
 			writeImportFile(t, dir, "second.yml", "definitions: {recap: {output: recap.md}}\n")
-			writeImportFile(t, dir, "profiles/testing.yml", "definitions: null\ncredential: "+credential+"\n")
-			result, err := Load[config](File(root), Options[config]{Imports: true, Profile: "testing"})
+			writeImportFile(t, dir, "overlays/testing.yml", "definitions: null\ncredential: "+credential+"\n")
+			result, err := testLoad[config](File(root), Options[config]{Imports: true, Overlay: "testing"})
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -148,8 +148,91 @@ func TestMetadataQueriesReturnDetachedRecords(t *testing.T) {
 	}
 }
 
+func TestResolutionInputKeepsDetachedEntryMetadata(t *testing.T) {
+	t.Parallel()
+
+	type configuration struct {
+		Default  string            `yaml:"default"`
+		Items    []string          `yaml:"items"`
+		Values   map[string]string `yaml:"values"`
+		Nullable *string           `yaml:"nullable"`
+	}
+	schema := mustSchemaFor[configuration](t)
+	document := parseDocumentForDecode(t, "items: [first]\nvalues: {'0': key, 'a/b~': escaped}\nnullable: null\n")
+	decoded, issues := decodeConfiguration(schema, reflect.ValueOf(configuration{Default: "retained"}), document)
+	if len(issues) != 0 {
+		t.Fatalf("decode issues = %#v", issues)
+	}
+	metadata := metadataFromDecoded(decoded)
+	input := newResolutionInput(metadata, decoded.final, []SourceInfo{{
+		ID: "source-1", Label: "decode.yml", Layer: LayerBase,
+		ImportedFrom: &Location{SourceID: "parent", Line: 1, Column: 1},
+	}})
+
+	parsedItem, err := ParsePath("/items/0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	parsedKey, err := ParsePath("/values/0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, path := range []Path{Path{}, Keys("default"), Keys("nullable"), parsedItem, parsedKey, Keys("values", "a/b~")} {
+		if _, ok := input.lookup(path); !ok {
+			t.Fatalf("entry path %s is missing", path)
+		}
+	}
+	defaultInfo, _ := input.lookup(Keys("default"))
+	nullInfo, _ := input.lookup(Keys("nullable"))
+	if defaultInfo.Explicit || !nullInfo.Explicit || !nullInfo.Null {
+		t.Fatalf("default = %#v, nullable = %#v", defaultInfo, nullInfo)
+	}
+	for _, path := range []Path{
+		Keys("default", "child"),
+		Keys("items", "0"),
+		Keys("values").Index(0),
+		Keys("items").Index(1),
+	} {
+		if _, ok := input.lookup(path); ok {
+			t.Fatalf("entry lookup accepted %s", path)
+		}
+	}
+
+	item, _ := input.lookup(parsedItem)
+	item.Origin.Locations[0].SourceID = "mutated"
+	source, ok := input.source("source-1")
+	if !ok {
+		t.Fatal("source is missing")
+	}
+	source.ImportedFrom.SourceID = "mutated"
+
+	configurationAtEntry := decoded.value.Interface().(configuration)
+	resolved := runResolution(&configurationAtEntry, func(value *configuration, resolution *Resolution) error {
+		value.Items[0] = "normalized"
+		resolution.Record(Keys("items"), ChangeNormalization, "normalized item")
+		return nil
+	}, schema, decoded, document, input)
+	if len(resolved.diagnostics) != 0 {
+		t.Fatalf("resolution diagnostics = %#v", resolved.diagnostics)
+	}
+	applyResolutionMetadata(&metadata, resolved)
+	metadata.effectivePaths = effectivePathIndex(resolved.final)
+
+	again, ok := input.lookup(parsedItem)
+	if !ok || again.Origin.Locations[0].SourceID != "source-1" || again.Origin.Operation != "" {
+		t.Fatalf("entry metadata changed after resolution = %#v, %v", again, ok)
+	}
+	againSource, ok := input.source("source-1")
+	if !ok || againSource.ImportedFrom == nil || againSource.ImportedFrom.SourceID != "parent" {
+		t.Fatalf("entry source changed = %#v, %v", againSource, ok)
+	}
+	if _, ok := input.source(""); ok {
+		t.Fatal("empty source identity resolved")
+	}
+}
+
 func TestQueriesRespectActualHistoricalAndEffectiveContainers(t *testing.T) {
-	result, err := Load[map[string]any](Bytes("base", []byte("items: [1]\nm: {'0': 2}\nx: 3\nretired: {child: 4}\n")), Options[map[string]any]{Overrides: []Override{{Path: Keys("retired"), Value: "removed", Flag: "--retired"}}})
+	result, err := testLoad[map[string]any](Bytes("base", []byte("items: [1]\nm: {'0': 2}\nx: 3\nretired: {child: 4}\n")), Options[map[string]any]{Overrides: []Override{{Path: Keys("retired"), Value: "removed", Flag: "--retired"}}})
 	if err != nil {
 		t.Fatal(err)
 	}

internal/engine/options.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 func selectOptions[T any](source Source, supplied []Options[T]) (Options[T], []Diagnostic) {
 	if len(supplied) > 1 {
@@ -10,8 +10,8 @@ func selectOptions[T any](source Source, supplied []Options[T]) (Options[T], []D
 	}
 	var diagnostics []Diagnostic
 	definition := options.Definition
-	if !validProfileName(options.Profile) {
-		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "profile name must contain only ASCII letters, digits, underscore, or hyphen"))
+	if !validOverlayName(options.Overlay) {
+		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "overlay name must contain only ASCII letters, digits, underscore, or hyphen"))
 	}
 	if options.Filesystem != nil {
 		diagnostics = append(diagnostics, filesystemOptionDiagnostics(source, options.Filesystem)...)
@@ -19,11 +19,11 @@ func selectOptions[T any](source Source, supplied []Options[T]) (Options[T], []D
 	if source.kind == sourceNone && options.Imports {
 		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource cannot enable imports"))
 	}
-	if source.kind == sourceNone && options.Profile != "" && options.Profile != "default" {
-		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource cannot select an active profile"))
+	if source.kind == sourceNone && options.Overlay != "" && options.Overlay != "default" {
+		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource cannot select an active overlay"))
 	}
-	if options.Filesystem == nil && (source.kind == sourceBytes || source.kind == sourceReader) && (options.Imports || activeProfile(options.Profile)) {
-		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "byte and reader imports or profiles require filesystem context"))
+	if options.Filesystem == nil && (source.kind == sourceBytes || source.kind == sourceReader) && (options.Imports || activeOverlay(options.Overlay)) {
+		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "byte and reader imports or overlays require filesystem context"))
 	}
 	if definition.Version != nil {
 		if !definition.Version.Path.valid() {

internal/engine/overlay.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"slices"
@@ -20,14 +20,14 @@ type displacedDefinition struct {
 func overlayDocuments(base *composedDocument, overlay *document.Node) (*composedDocument, []Diagnostic) {
 	if base == nil || base.root == nil || base.root.Kind != document.Mapping || overlay == nil || overlay.Kind != document.Mapping {
 		return nil, []Diagnostic{{
-			Code: CodeProfileInvalid, Severity: SeverityError,
-			Message: "profile overlay requires mapping document roots",
+			Code: CodeOverlayInvalid, Severity: SeverityError,
+			Message: "overlay requires mapping document roots",
 		}}
 	}
 	result := cloneComposedDocument(base)
-	mergeOverlayOrigin(result.origins, Path{}, overlay.Location, LayerProfile)
-	mergeOverlayMappings(result, result.root, overlay, Path{}, LayerProfile, true)
-	result.applications = append(result.applications, historyApplication{layer: LayerProfile, value: overlay})
+	mergeOverlayOrigin(result.origins, Path{}, overlay.Location, LayerOverlay)
+	mergeOverlayMappings(result, result.root, overlay, Path{}, LayerOverlay, true)
+	result.applications = append(result.applications, historyApplication{layer: LayerOverlay, value: overlay})
 	return result, nil
 }
 

internal/engine/overlay_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"reflect"
@@ -22,7 +22,7 @@ to_scalar: {child: old}
 	}
 	overlay := parseCompositionDocument(t, "source-2", `shared:
   changed: new
-  added: profile
+  added: overlay
 sequence: []
 nullable: null
 to_map: {child: new}
@@ -42,7 +42,7 @@ to_scalar: scalar
 	}{
 		{path: Keys("shared", "kept"), kind: document.String, text: "base"},
 		{path: Keys("shared", "changed"), kind: document.String, text: "new"},
-		{path: Keys("shared", "added"), kind: document.String, text: "profile"},
+		{path: Keys("shared", "added"), kind: document.String, text: "overlay"},
 		{path: Keys("sequence"), kind: document.Sequence},
 		{path: Keys("nullable"), kind: document.Null},
 		{path: Keys("to_map"), kind: document.Mapping},
@@ -62,7 +62,7 @@ to_scalar: scalar
 		t.Fatal("parent replacement retained a stale child origin")
 	}
 	shared := result.origins["/shared"]
-	if shared.Layer != LayerProfile || len(shared.Locations) != 2 {
+	if shared.Layer != LayerOverlay || len(shared.Locations) != 2 {
 		t.Fatalf("shared mapping origin = %#v", shared)
 	}
 	if len(result.overlays) != 5 {

internal/engine/override.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"strconv"

internal/engine/override_apply.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"slices"

internal/engine/override_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -41,9 +41,9 @@ func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *te
   labels: {base: retained}
   api_key: BASE_SECRET
 `)
-	writeImportFile(t, directory, filepath.Join("profiles", "testing.yml"), `settings:
-  target: profile
-  labels: {profile: retained}
+	writeImportFile(t, directory, filepath.Join("overlays", "testing.yml"), `settings:
+  target: overlay
+  labels: {overlay: retained}
 `)
 	validated := false
 	overrides := []Override{
@@ -56,13 +56,13 @@ func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *te
 		{Path: Keys("settings", "labels"), Value: map[string]any{"cli": "selected"}, Flag: "--label"},
 		{Path: Keys("settings", "api_key"), Value: "CLI_SECRET", Flag: "--api-key-env"},
 	}
-	result, err := loadWithSecretLookup(File(mainPath), func(name string) (string, bool) {
+	result, err := testLoadWithSecretLookup(File(mainPath), func(name string) (string, bool) {
 		if name != "CLI_SECRET" {
 			t.Fatalf("looked up superseded secret name %q", name)
 		}
 		return "credential-value", true
 	}, Options[overrideLifecycleConfig]{
-		Imports: true, Profile: "testing", Overrides: overrides,
+		Imports: true, Overlay: "testing", Overrides: overrides,
 		Definition: Definition[overrideLifecycleConfig]{
 			Defaults: func() overrideLifecycleConfig {
 				return overrideLifecycleConfig{Settings: overrideLifecycleSettings{Target: "default", Count: 9, Text: "default", Items: []string{"default"}}}
@@ -83,10 +83,10 @@ func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *te
 		},
 	})
 	if err != nil {
-		t.Fatalf("loadWithSecretLookup() error = %v", err)
+		t.Fatalf("testLoadWithSecretLookup() error = %v", err)
 	}
 	want := overrideLifecycleSettings{
-		Target: "cli", Labels: map[string]string{"base": "retained", "profile": "retained", "cli": "selected"},
+		Target: "cli", Labels: map[string]string{"base": "retained", "overlay": "retained", "cli": "selected"},
 		APIKey: result.Config.Settings.APIKey,
 	}
 	if !validated || result.Config.Settings.Count != 0 || result.Config.Settings.Enabled || result.Config.Settings.Text != "" ||
@@ -95,7 +95,7 @@ func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *te
 		t.Fatalf("effective settings = %#v", result.Config.Settings)
 	}
 	sources := result.Sources()
-	if len(sources) != 3+len(overrides) || sources[0].Layer != LayerBase || sources[1].Layer != LayerBase || sources[2].Layer != LayerProfile {
+	if len(sources) != 3+len(overrides) || sources[0].Layer != LayerBase || sources[1].Layer != LayerBase || sources[2].Layer != LayerOverlay {
 		t.Fatalf("sources = %#v", sources)
 	}
 	for index, override := range overrides {
@@ -104,7 +104,7 @@ func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *te
 		}
 	}
 	history := result.Metadata().History(Keys("settings", "target"))
-	wantLayers := []Layer{LayerDefault, LayerBase, LayerProfile, LayerCLI, LayerResolution}
+	wantLayers := []Layer{LayerDefault, LayerBase, LayerOverlay, LayerCLI, LayerResolution}
 	if got := historyLayers(history); !reflect.DeepEqual(got, wantLayers) {
 		t.Fatalf("target history layers = %#v, want %#v; history %#v", got, wantLayers, history)
 	}
@@ -123,7 +123,7 @@ func TestOverridesSupportDefaultsOnlyMapMergeListReplacementAndNumericKeys(t *te
 		"int": int8(1), "uint": uint16(2), "float": float32(3.5), "bool": false,
 		"null": nil, "list": []any{"value"}, "map": map[string]any{"key": "value"},
 	}
-	result, err := Load(NoSource(), Options[config]{
+	result, err := testLoad(NoSource(), Options[config]{
 		Definition: Definition[config]{Defaults: func() config {
 			return config{Labels: map[string]string{"kept": "default"}, Items: []int{9}}
 		}},
@@ -194,7 +194,7 @@ func TestOverrideValidationRejectsPathsOverlapValuesAndProtectedTargets(t *testi
 		{name: "label", overrides: []Override{{Path: Keys("scalar"), Value: "x", Flag: "\nCANARY"}}, code: CodeOverrideInvalidLabel},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			result, err := Load(base, Options[config]{Definition: Definition[config]{Version: version}, Overrides: test.overrides})
+			result, err := testLoad(base, Options[config]{Definition: Definition[config]{Version: version}, Overrides: test.overrides})
 			if result != nil {
 				t.Fatalf("result = %#v, want nil", result)
 			}
@@ -213,7 +213,7 @@ func TestOverrideCannotReplaceSchemaVersionAncestor(t *testing.T) {
 	type config struct {
 		Schema schemaConfig `yaml:"schema"`
 	}
-	_, err := Load(Bytes("version.yml", []byte("schema: {version: 4}\n")), Options[config]{
+	_, err := testLoad(Bytes("version.yml", []byte("schema: {version: 4}\n")), Options[config]{
 		Definition: Definition[config]{Version: &VersionRule{Path: Keys("schema", "version"), Check: func(Version, *Validation) error { return nil }}},
 		Overrides:  []Override{{Path: Keys("schema"), Value: map[string]any{"other": "value"}, Flag: "--schema"}},
 	})
@@ -224,7 +224,7 @@ func TestOverrideDecodeFailureUsesFlagSourceWithoutRawValue(t *testing.T) {
 	type config struct {
 		Count int `yaml:"count"`
 	}
-	result, err := Load(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
+	result, err := testLoad(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
 		Path: Keys("missing"), Value: "RAW-ARG-CANARY", Flag: "--missing",
 	}}})
 	if result != nil {
@@ -249,7 +249,7 @@ func TestOverrideTypeMismatchUsesNormalStrictDecode(t *testing.T) {
 	type config struct {
 		Count int `yaml:"count"`
 	}
-	_, err := Load(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
+	_, err := testLoad(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
 		Path: Keys("count"), Value: "not-an-integer", Flag: "--count",
 	}}})
 	loadError := requireSecretLoadCode(t, err, CodeDecodeType)
@@ -262,7 +262,7 @@ func TestOverrideEqualReplacementStillAppearsInHistory(t *testing.T) {
 	type config struct {
 		Value string `yaml:"value"`
 	}
-	result, err := Load(Bytes("equal.yml", []byte("value: same\n")), Options[config]{Overrides: []Override{{Path: Keys("value"), Value: "same", Flag: "--value"}}})
+	result, err := testLoad(Bytes("equal.yml", []byte("value: same\n")), Options[config]{Overrides: []Override{{Path: Keys("value"), Value: "same", Flag: "--value"}}})
 	if err != nil {
 		t.Fatal(err)
 	}

internal/engine/override_value.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"math"

internal/engine/parse.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"

internal/engine/parse_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"strings"

internal/engine/path.go

@@ -0,0 +1,148 @@
+package engine
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+)
+
+// Path identifies a configuration value using YAML field names. Its textual form
+// is a JSON Pointer: the root is empty, ~ escapes as ~0, and / escapes as ~1.
+// Paths are semantic rather than filesystem or URL paths: empty, dot, dot-dot,
+// percent-containing, and numeric keys retain their literal meaning. Parsed
+// numeric tokens are resolved only when traversal knows their containing type.
+//
+// Paths are immutable. The zero value is the root path.
+type Path struct {
+	segments []pathSegment
+	invalid  bool
+}
+
+type pathSegmentKind uint8
+
+const (
+	pathSegmentKey pathSegmentKind = iota
+	pathSegmentIndex
+	pathSegmentParsed
+)
+
+type pathSegment struct {
+	kind  pathSegmentKind
+	key   string
+	index int
+}
+
+// Keys constructs a path of mapping keys. Keys with no arguments returns the
+// root path.
+func Keys(keys ...string) Path {
+	p := Path{}
+	for _, key := range keys {
+		p = p.Key(key)
+	}
+	return p
+}
+
+// ParsePath parses a JSON Pointer. Numeric tokens remain unresolved until schema
+// or document traversal determines whether the containing value is a mapping or
+// sequence.
+func ParsePath(pointer string) (Path, error) {
+	if pointer == "" {
+		return Path{}, nil
+	}
+	if pointer[0] != '/' {
+		return Path{}, errors.New("configkit: path must be empty or begin with slash")
+	}
+
+	parts := strings.Split(pointer[1:], "/")
+	segments := make([]pathSegment, 0, len(parts))
+	for _, part := range parts {
+		key, ok := unescapePathToken(part)
+		if !ok {
+			return Path{}, errors.New("configkit: path contains an invalid tilde escape")
+		}
+		segments = append(segments, pathSegment{kind: pathSegmentParsed, key: key})
+	}
+	return Path{segments: segments}, nil
+}
+
+// Key returns a new path with key appended as a mapping-key segment.
+func (p Path) Key(key string) Path {
+	segments := clonePathSegments(p.segments, 1)
+	segments = append(segments, pathSegment{kind: pathSegmentKey, key: key})
+	return Path{segments: segments, invalid: p.invalid}
+}
+
+// Index returns a new path with index appended as a sequence-index segment.
+// A negative index produces an invalid path that configuration operations reject.
+func (p Path) Index(index int) Path {
+	segments := clonePathSegments(p.segments, 1)
+	segments = append(segments, pathSegment{kind: pathSegmentIndex, index: index})
+	return Path{segments: segments, invalid: p.invalid || index < 0}
+}
+
+// String returns the path's canonical JSON Pointer spelling.
+func (p Path) String() string {
+	if len(p.segments) == 0 {
+		return ""
+	}
+
+	var b strings.Builder
+	for _, segment := range p.segments {
+		b.WriteByte('/')
+		if segment.kind == pathSegmentIndex {
+			b.WriteString(strconv.Itoa(segment.index))
+			continue
+		}
+		b.WriteString(escapePathToken(segment.key))
+	}
+	return b.String()
+}
+
+func (p Path) clone() Path {
+	return Path{segments: clonePathSegments(p.segments, 0), invalid: p.invalid}
+}
+
+func (p Path) valid() bool {
+	return !p.invalid
+}
+
+func clonePathSegments(segments []pathSegment, extra int) []pathSegment {
+	if len(segments) == 0 && extra == 0 {
+		return nil
+	}
+	cloned := make([]pathSegment, len(segments), len(segments)+extra)
+	copy(cloned, segments)
+	return cloned
+}
+
+func escapePathToken(token string) string {
+	token = strings.ReplaceAll(token, "~", "~0")
+	return strings.ReplaceAll(token, "/", "~1")
+}
+
+func unescapePathToken(token string) (string, bool) {
+	if !strings.Contains(token, "~") {
+		return token, true
+	}
+
+	var b strings.Builder
+	for i := 0; i < len(token); i++ {
+		if token[i] != '~' {
+			b.WriteByte(token[i])
+			continue
+		}
+		if i+1 >= len(token) {
+			return "", false
+		}
+		i++
+		switch token[i] {
+		case '0':
+			b.WriteByte('~')
+		case '1':
+			b.WriteByte('/')
+		default:
+			return "", false
+		}
+	}
+	return b.String(), true
+}

internal/engine/path_fuzz_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "testing"
 

internal/engine/path_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import "testing"
 

internal/engine/projection.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"cmp"
@@ -199,7 +199,7 @@ func (o *valueOperation) project(value reflect.Value, descriptor *typeDescriptor
 	case descriptorSecret:
 		node, issue := o.node(document.String, path, depth)
 		if issue == nil {
-			node.Text = value.Interface().(Secret).EnvName()
+			node.Text = o.schema.secrets.Read(value).Name
 		}
 		return node, issue
 	case descriptorText:

internal/engine/projection_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -359,9 +359,9 @@ func TestCompareDocumentTreesTracksSemanticChanges(t *testing.T) {
 
 func mustSchemaFor[T any](t *testing.T) *schemaDescriptor {
 	t.Helper()
-	schema, issue := buildSchema(reflect.TypeFor[T]())
+	schema, issue := testBuildSchema(reflect.TypeFor[T]())
 	if issue != nil {
-		t.Fatalf("buildSchema() issue = %#v", issue)
+		t.Fatalf("testBuildSchema() issue = %#v", issue)
 	}
 	return schema
 }

internal/engine/provenance_test.go

@@ -0,0 +1,510 @@
+package engine
+
+import (
+	"errors"
+	"reflect"
+	"strings"
+	"sync"
+	"testing"
+)
+
+type layeredItem struct {
+	Value string `yaml:"value"`
+}
+
+type layeredConfig struct {
+	Shared struct {
+		Equal    string `yaml:"equal"`
+		Imported string `yaml:"imported"`
+		Overlay  string `yaml:"overlay"`
+	} `yaml:"shared"`
+	Values   []int                  `yaml:"values"`
+	Items    map[string]layeredItem `yaml:"items"`
+	Value    any                    `yaml:"value"`
+	Nullable *string                `yaml:"nullable"`
+	Derived  int                    `yaml:"derived"`
+	Empty    map[string]string      `yaml:"empty"`
+}
+
+func TestLayeredProvenanceAgreesWithResolvedSnapshot(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports: [{path: imported.yml}]
+shared: {equal: same}
+values: [1, 2]
+items:
+  keep: {value: 'yes'}
+  remove: {value: 'no'}
+value: {child: base}
+nullable: base
+empty: {}
+`)
+	importPath := writeImportFile(t, directory, "imported.yml", "shared: {imported: base}\n")
+	overlayPath := writeImportFile(t, directory, "overlays/testing.yml", `shared: {overlay: selected}
+values: [3, 4]
+value: selected
+nullable: null
+empty: {}
+`)
+	defaultNullable := "default"
+	definition := Definition[layeredConfig]{
+		Defaults: func() layeredConfig {
+			defaults := layeredConfig{
+				Values: []int{0, 0}, Value: map[string]any{"child": "default"},
+				Nullable: &defaultNullable, Empty: map[string]string{"retained": "default"},
+			}
+			defaults.Shared.Equal = "same"
+			return defaults
+		},
+		Resolve: func(configuration *layeredConfig, resolution *Resolution) error {
+			Normalize(resolution, Keys("values"), &configuration.Values, []int{5},
+				"bounded values", Keys("shared", "imported"), Keys("shared", "imported"))
+			Normalize(resolution, Keys("values"), &configuration.Values, []int{5},
+				"bounded values", Keys("shared", "imported"))
+			delete(configuration.Items, "remove")
+			resolution.Record(Keys("items"), ChangeNormalization, "removed disabled items")
+			Default(resolution, Keys("derived"), &configuration.Derived, 7,
+				"derived from equal", Keys("shared", "equal"), Keys("shared", "equal"))
+			resolution.Warning(Keys("values"), "values were bounded", Keys("shared", "imported"))
+			return nil
+		},
+	}
+
+	result, err := testLoad[layeredConfig](File(mainPath), Options[layeredConfig]{
+		Imports: true, Overlay: "testing", Definition: definition,
+	})
+	if err != nil {
+		var loadError *LoadError
+		_ = errors.As(err, &loadError)
+		t.Fatalf("%v: %#v", err, loadError.Diagnostics())
+	}
+	wantSources := []string{canonicalTestPath(t, mainPath), canonicalTestPath(t, importPath), canonicalTestPath(t, overlayPath)}
+	sources := result.Sources()
+	gotSources := make([]string, len(sources))
+	for index, source := range sources {
+		gotSources[index] = source.Path
+	}
+	if !reflect.DeepEqual(gotSources, wantSources) || sources[2].Layer != LayerOverlay {
+		t.Fatalf("sources = %#v", sources)
+	}
+	if result.Config.Shared.Equal != "same" || result.Config.Shared.Imported != "base" || result.Config.Shared.Overlay != "selected" ||
+		!reflect.DeepEqual(result.Config.Values, []int{5}) || result.Config.Nullable != nil || result.Config.Derived != 7 ||
+		result.Config.Empty["retained"] != "default" {
+		t.Fatalf("configuration = %#v", result.Config)
+	}
+
+	metadata := result.Metadata()
+	equal, _ := metadata.Lookup(Keys("shared", "equal"))
+	derived, _ := metadata.Lookup(Keys("derived"))
+	nullable, _ := metadata.Lookup(Keys("nullable"))
+	empty, _ := metadata.Lookup(Keys("empty"))
+	firstValue, _ := metadata.Lookup(Keys("values").Index(0))
+	if !equal.Explicit || equal.Origin.Layer != LayerBase || derived.Explicit || derived.Origin.Operation != ChangeDerivedDefault ||
+		!nullable.Explicit || !nullable.Null || nullable.Origin.Layer != LayerOverlay ||
+		!empty.Explicit || empty.Origin.Layer != LayerOverlay || len(empty.Origin.Locations) != 2 ||
+		!firstValue.Explicit || firstValue.Origin.Operation != ChangeNormalization {
+		t.Fatalf("metadata = equal %#v derived %#v nullable %#v empty %#v value %#v", equal, derived, nullable, empty, firstValue)
+	}
+	if _, ok := metadata.Lookup(Keys("value", "child")); ok {
+		t.Fatal("overlay-removed child remains effective")
+	}
+	if _, ok := metadata.Lookup(Keys("values").Index(1)); ok {
+		t.Fatal("resolution-removed sequence index remains effective")
+	}
+	if _, ok := metadata.Lookup(Keys("items", "remove", "value")); ok {
+		t.Fatal("resolution-removed mapping child remains effective")
+	}
+
+	assertHistoryLayersAndPaths(t, metadata.History(Keys("values").Index(1)),
+		[]Layer{LayerDefault, LayerBase, LayerOverlay, LayerResolution},
+		[]string{"/values/1", "/values/1", "/values", "/values"})
+	assertHistoryLayersAndPaths(t, metadata.History(Keys("value", "child")),
+		[]Layer{LayerDefault, LayerBase, LayerOverlay},
+		[]string{"/value/child", "/value/child", "/value"})
+	removedHistory := metadata.History(Keys("items", "remove", "value"))
+	assertHistoryLayersAndPaths(t, removedHistory,
+		[]Layer{LayerBase, LayerResolution},
+		[]string{"/items/remove/value", "/items"})
+	if !reflect.DeepEqual(removedHistory[1].Reasons, []string{"removed disabled items"}) {
+		t.Fatalf("removed history = %#v", removedHistory)
+	}
+	valuesHistory := metadata.History(Keys("values").Index(0))
+	lastValue := valuesHistory[len(valuesHistory)-1]
+	if !reflect.DeepEqual(lastValue.Reasons, []string{"bounded values"}) || len(lastValue.Dependencies) != 1 || lastValue.Dependencies[0].String() != "/shared/imported" {
+		t.Fatalf("canonical resolution history = %#v", lastValue)
+	}
+
+	schema, issue := testBuildSchema(reflect.TypeFor[layeredConfig]())
+	if issue != nil {
+		t.Fatal(issue)
+	}
+	projected, projectionIssue := projectConfiguration(schema, reflect.ValueOf(result.Config), defaultProjectionLimits())
+	if projectionIssue != nil || !configurationValuesEqual(projected, result.final) {
+		t.Fatalf("typed projection and private snapshot disagree: %#v", projectionIssue)
+	}
+
+	metadata.history[Keys("values").Index(0).String()][0].Origin.Layer = "mutated"
+	sources[1].ImportedFrom.SourceID = "mutated"
+	diagnostics := result.Diagnostics()
+	diagnostics[0].Related[0].SourceID = "mutated"
+	result.Config.Values[0] = 99
+	freshHistory := result.Metadata().History(Keys("values").Index(0))
+	if freshHistory[0].Origin.Layer == "mutated" || result.Sources()[1].ImportedFrom.SourceID == "mutated" ||
+		result.Diagnostics()[0].Related[0].SourceID == "mutated" {
+		t.Fatal("returned inspection records alias private state")
+	}
+	snapshotValue, ok := documentAtPath(result.final, Keys("values").Index(0))
+	if !ok || snapshotValue.Text != "5" {
+		t.Fatal("caller configuration mutation changed the private final snapshot")
+	}
+}
+
+func TestSelectedOverlayLoadsRemainIndependentConcurrently(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", "values: [1, 2]\n")
+	writeImportFile(t, directory, "overlays/testing.yml", "values: [3, 4]\n")
+	options := Options[layeredConfig]{Overlay: "testing"}
+
+	const loads = 16
+	results := make(chan *testResult[layeredConfig], loads)
+	errors := make(chan error, loads)
+	var group sync.WaitGroup
+	for index := 0; index < loads; index++ {
+		group.Add(1)
+		go func() {
+			defer group.Done()
+			result, err := testLoad[layeredConfig](File(mainPath), options)
+			if err != nil {
+				errors <- err
+				return
+			}
+			results <- result
+		}()
+	}
+	group.Wait()
+	close(results)
+	close(errors)
+	for err := range errors {
+		t.Fatal(err)
+	}
+	var collected []*testResult[layeredConfig]
+	for result := range results {
+		collected = append(collected, result)
+	}
+	if len(collected) != loads {
+		t.Fatalf("completed loads = %d", len(collected))
+	}
+	collected[0].Config.Values[0] = 99
+	collected[0].metadata.fields[Keys("values").String()] = FieldInfo{}
+	for _, result := range collected[1:] {
+		if !reflect.DeepEqual(result.Config.Values, []int{3, 4}) {
+			t.Fatalf("concurrent result contaminated = %#v", result.Config.Values)
+		}
+		if info, ok := result.Metadata().Lookup(Keys("values")); !ok || info.Origin.Layer != LayerOverlay {
+			t.Fatalf("concurrent metadata contaminated = %#v, %v", info, ok)
+		}
+	}
+}
+
+func TestResolutionInputKeepsLayeredOriginsAndSources(t *testing.T) {
+	directory := t.TempDir()
+	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
+  imports: [{path: first.yml}, {path: second.yml}]
+main: main
+equal: same
+cli_equal: same
+composite: {main: main}
+`)
+	firstPath := writeImportFile(t, directory, "first.yml", `imported: imported
+sequence: [first, second]
+composite: {first: first}
+`)
+	secondPath := writeImportFile(t, directory, "second.yml", "composite: {second: second}\n")
+	overlayPath := writeImportFile(t, directory, "overlays/testing.yml", "equal: same\noverlay: overlay\n")
+	compositeSources := map[string]bool{
+		canonicalTestPath(t, mainPath):   true,
+		canonicalTestPath(t, firstPath):  true,
+		canonicalTestPath(t, secondPath): true,
+	}
+	type config struct {
+		Main      string            `yaml:"main"`
+		Imported  string            `yaml:"imported"`
+		Sequence  []string          `yaml:"sequence"`
+		Composite map[string]string `yaml:"composite"`
+		Equal     string            `yaml:"equal"`
+		Overlay   string            `yaml:"overlay"`
+		CLIEqual  string            `yaml:"cli_equal"`
+	}
+	var callbackErr error
+	result, err := testLoad[config](File(mainPath), Options[config]{
+		Imports: true, Overlay: "testing", Overrides: []Override{{Path: Keys("cli_equal"), Value: "same", Flag: "--cli-equal"}},
+		Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+			check := func(ok bool, message string) {
+				if !ok && callbackErr == nil {
+					callbackErr = errors.New(message)
+				}
+			}
+			fileOwner := func(path Path, want string) FieldInfo {
+				info, found := resolution.InputInfo(path)
+				check(found && len(info.Origin.Locations) == 1, "scalar has no exact origin")
+				if !found || len(info.Origin.Locations) != 1 {
+					return FieldInfo{}
+				}
+				source, exists := resolution.Source(info.Origin.Locations[0].SourceID)
+				check(exists && source.Path == want, "scalar source does not match its declaration")
+				return info
+			}
+			fileOwner(Keys("main"), canonicalTestPath(t, mainPath))
+			fileOwner(Keys("imported"), canonicalTestPath(t, firstPath))
+			fileOwner(Keys("sequence").Index(1), canonicalTestPath(t, firstPath))
+			overlay := fileOwner(Keys("equal"), canonicalTestPath(t, overlayPath))
+			fileOwner(Keys("overlay"), canonicalTestPath(t, overlayPath))
+			check(overlay.Origin.Layer == LayerOverlay, "overlay replacement retained base ownership")
+			cli, found := resolution.InputInfo(Keys("cli_equal"))
+			check(found && cli.Origin.Layer == LayerCLI && len(cli.Origin.Locations) == 1, "CLI replacement lost ownership")
+			if found && len(cli.Origin.Locations) == 1 {
+				source, exists := resolution.Source(cli.Origin.Locations[0].SourceID)
+				check(exists && source.Layer == LayerCLI && source.Path == "", "CLI source has a file path or is missing")
+			}
+
+			composite, found := resolution.InputInfo(Keys("composite"))
+			check(found && len(composite.Origin.Locations) == 3, "composite mapping did not retain every contributor")
+			for _, location := range composite.Origin.Locations {
+				source, exists := resolution.Source(location.SourceID)
+				check(exists && compositeSources[source.Path], "composite location has no expected source record")
+				delete(compositeSources, source.Path)
+			}
+			check(len(compositeSources) == 0, "composite sources are incomplete")
+
+			imported, _ := resolution.InputInfo(Keys("imported"))
+			importedSourceID := imported.Origin.Locations[0].SourceID
+			imported.Origin.Locations[0].SourceID = "mutated"
+			importSource, _ := resolution.Source(importedSourceID)
+			check(importSource.ImportedFrom != nil, "import source is missing its import location")
+			if importSource.ImportedFrom != nil {
+				importSource.ImportedFrom.SourceID = "mutated"
+			}
+			again, _ := resolution.InputInfo(Keys("imported"))
+			againSource, _ := resolution.Source(importedSourceID)
+			check(again.Origin.Locations[0].SourceID == importedSourceID, "input record is aliased")
+			check(againSource.ImportedFrom != nil && againSource.ImportedFrom.SourceID == "source-1", "source record is aliased")
+			return callbackErr
+		}},
+	})
+	if callbackErr != nil {
+		t.Fatal(callbackErr)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Config.Main != "main" || result.Config.Imported != "imported" || !reflect.DeepEqual(result.Config.Sequence, []string{"first", "second"}) ||
+		result.Config.Equal != "same" || result.Config.Overlay != "overlay" || result.Config.CLIEqual != "same" {
+		t.Fatalf("configuration = %#v", result.Config)
+	}
+
+	resultField, _ := result.Metadata().Lookup(Keys("imported"))
+	resultSource := result.Sources()[1]
+	if resultField.Origin.Locations[0].SourceID != "source-2" || resultSource.ImportedFrom == nil || resultSource.ImportedFrom.SourceID != "source-1" {
+		t.Fatal("callback record mutation changed the completed result")
+	}
+}
+
+func TestResolutionInputUsesEntryShapesAcrossTypedAndDynamicValues(t *testing.T) {
+	t.Parallel()
+
+	type Embedded struct {
+		Name string `yaml:"name"`
+	}
+	type config struct {
+		Embedded `yaml:",inline"`
+		Mappings map[string]string `yaml:"mappings"`
+		Array    [2]string         `yaml:"array"`
+		Dynamic  any               `yaml:"dynamic"`
+	}
+	var callbackErr error
+	_, err := testLoad[config](Bytes("shapes.yml", []byte("name: inlined\nmappings: {'-0': key, 'a/b~': escaped}\narray: [zero, one]\ndynamic: {nested: [dynamic]}\n")), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+		check := func(path Path, want bool) {
+			_, found := resolution.InputInfo(path)
+			if found != want && callbackErr == nil {
+				callbackErr = errors.New("entry shape lookup disagrees with its document container")
+			}
+		}
+		parsedMapping, _ := ParsePath("/mappings/-0")
+		escapedMapping, _ := ParsePath("/mappings/a~1b~0")
+		check(Keys("name"), true)
+		check(parsedMapping, true)
+		check(escapedMapping, true)
+		check(Keys("mappings").Index(0), false)
+		check(Keys("array").Index(1), true)
+		check(Keys("array", "1"), false)
+		check(Keys("array").Index(2), false)
+		check(Keys("dynamic", "nested").Index(0), true)
+		check(Keys("dynamic", "nested", "0"), false)
+		negative, _ := ParsePath("/array/-1")
+		check(negative, false)
+		return callbackErr
+	}}})
+	if callbackErr != nil {
+		t.Fatal(callbackErr)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestResolutionInputDistinguishesNonFileRootsAndImportedFiles(t *testing.T) {
+	directory := t.TempDir()
+	importPath := writeImportFile(t, directory, "fragment.yml", "imported: file\n")
+	type config struct {
+		Root     string `yaml:"root"`
+		Imported string `yaml:"imported"`
+		Default  string `yaml:"default"`
+	}
+	input := "configkit: {imports: [{path: fragment.yml}]}\nroot: memory\n"
+	context := &FilesystemContext{BaseDir: directory, Root: directory}
+	for _, test := range []struct {
+		name   string
+		source func() Source
+	}{
+		{name: "bytes", source: func() Source { return Bytes("memory://config.yml", []byte(input)) }},
+		{name: "reader", source: func() Source { return Reader("memory://config.yml", strings.NewReader(input)) }},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			var callbackErr error
+			_, err := testLoad[config](test.source(), Options[config]{Imports: true, Filesystem: context, Definition: Definition[config]{
+				Defaults: func() config { return config{Default: "retained"} },
+				Resolve: func(_ *config, resolution *Resolution) error {
+					root, _ := resolution.InputInfo(Keys("root"))
+					imported, _ := resolution.InputInfo(Keys("imported"))
+					defaulted, _ := resolution.InputInfo(Keys("default"))
+					rootSource, rootFound := resolution.Source(root.Origin.Locations[0].SourceID)
+					importSource, importFound := resolution.Source(imported.Origin.Locations[0].SourceID)
+					if !rootFound || rootSource.Path != "" || !importFound || importSource.Path != canonicalTestPath(t, importPath) || defaulted.Explicit {
+						callbackErr = errors.New("non-file root or imported file provenance is wrong")
+					}
+					if _, found := resolution.Source("unknown"); found {
+						callbackErr = errors.New("unknown source was found")
+					}
+					return callbackErr
+				},
+			}})
+			if callbackErr != nil {
+				t.Fatal(callbackErr)
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+
+	var callbackErr error
+	_, err := testLoad[config](Bytes("memory://standalone.yml", []byte("root: memory\n")), Options[config]{Definition: Definition[config]{
+		Defaults: func() config { return config{Default: "retained"} },
+		Resolve: func(_ *config, resolution *Resolution) error {
+			root, rootFound := resolution.InputInfo(Keys("root"))
+			defaulted, defaultFound := resolution.InputInfo(Keys("default"))
+			source, sourceFound := resolution.Source(root.Origin.Locations[0].SourceID)
+			if !rootFound || !defaultFound || !sourceFound || source.Path != "" || defaulted.Explicit {
+				callbackErr = errors.New("standalone non-file provenance is wrong")
+			}
+			return callbackErr
+		},
+	}})
+	if callbackErr != nil {
+		t.Fatal(callbackErr)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestResolutionInputRemainsFixedAcrossRecordedMutations(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Existing string            `yaml:"existing"`
+		Values   map[string]string `yaml:"values"`
+	}
+	var callbackErr error
+	result, err := testLoad[config](Bytes("mutations.yml", []byte("existing: original\nvalues: {original: move}\n")), Options[config]{Definition: Definition[config]{Resolve: func(value *config, resolution *Resolution) error {
+		original, originalFound := resolution.InputInfo(Keys("values", "original"))
+		_, destinationFound := resolution.InputInfo(Keys("values", "destination"))
+		existing, existingFound := resolution.InputInfo(Keys("existing"))
+		Normalize(resolution, Keys("existing"), &value.Existing, "normalized", "normalized existing value")
+		value.Values["destination"] = value.Values["original"]
+		delete(value.Values, "original")
+		resolution.Record(Keys("values"), ChangeNormalization, "moved configured value")
+		againOriginal, againOriginalFound := resolution.InputInfo(Keys("values", "original"))
+		againDestination, againDestinationFound := resolution.InputInfo(Keys("values", "destination"))
+		againExisting, againExistingFound := resolution.InputInfo(Keys("existing"))
+		if !originalFound || destinationFound || !existingFound || !againOriginalFound || againDestinationFound || !againExistingFound ||
+			!reflect.DeepEqual(original, againOriginal) || !reflect.DeepEqual(existing, againExisting) || !reflect.DeepEqual(againDestination, FieldInfo{}) {
+			callbackErr = errors.New("entry view changed during resolution")
+		}
+		return callbackErr
+	}}})
+	if callbackErr != nil {
+		t.Fatal(callbackErr)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Config.Existing != "normalized" || result.Config.Values["destination"] != "move" {
+		t.Fatalf("configuration = %#v", result.Config)
+	}
+	if _, found := result.Metadata().Lookup(Keys("values", "original")); found {
+		t.Fatal("final metadata retained a removed path")
+	}
+	destination, found := result.Metadata().Lookup(Keys("values", "destination"))
+	existing, existingFound := result.Metadata().Lookup(Keys("existing"))
+	if !found || destination.Origin.Layer != LayerResolution || !existingFound || existing.Origin.Layer != LayerResolution {
+		t.Fatalf("final metadata = destination %#v existing %#v", destination, existing)
+	}
+}
+
+func TestResolutionInputQueriesRemainIndependentAcrossLoads(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Value string `yaml:"value"`
+	}
+	const loads = 16
+	failures := make(chan error, loads)
+	var group sync.WaitGroup
+	for index := 0; index < loads; index++ {
+		group.Add(1)
+		go func() {
+			defer group.Done()
+			_, err := testLoad[config](Bytes("parallel.yml", []byte("value: stable\n")), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+				info, found := resolution.InputInfo(Keys("value"))
+				source, sourceFound := resolution.Source(info.Origin.Locations[0].SourceID)
+				if !found || !sourceFound || source.ID != "source-1" {
+					return errors.New("independent entry lookup failed")
+				}
+				info.Origin.Locations[0].SourceID = "mutated"
+				source.Label = "mutated"
+				return nil
+			}}})
+			if err != nil {
+				failures <- err
+			}
+		}()
+	}
+	group.Wait()
+	close(failures)
+	for err := range failures {
+		t.Fatal(err)
+	}
+}
+
+func assertHistoryLayersAndPaths(t *testing.T, history []Change, layers []Layer, paths []string) {
+	t.Helper()
+	if len(history) != len(layers) || len(history) != len(paths) {
+		t.Fatalf("history = %#v", history)
+	}
+	for index, change := range history {
+		if change.Origin.Layer != layers[index] || change.Path.String() != paths[index] {
+			t.Fatalf("history[%d] = %#v", index, change)
+		}
+	}
+}

internal/engine/records.go

@@ -0,0 +1,286 @@
+package engine
+
+// Layer identifies the precedence layer responsible for a configuration value.
+type Layer string
+
+const (
+	LayerDefault    Layer = "default"
+	LayerBase       Layer = "base"
+	LayerOverlay    Layer = "overlay"
+	LayerCLI        Layer = "cli"
+	LayerResolution Layer = "resolution"
+)
+
+// ChangeKind identifies a recorded operation. The zero value is
+// used for input and default origins.
+type ChangeKind string
+
+const (
+	// ChangeDecoding records the built-in transition to canonical typed values.
+	// It is inspection metadata, not an operation accepted by Resolution.Record.
+	ChangeDecoding       ChangeKind = "decoding"
+	ChangeDerivedDefault ChangeKind = "derived_default"
+	ChangeNormalization  ChangeKind = "normalization"
+)
+
+// Severity classifies a diagnostic.
+type Severity string
+
+const (
+	SeverityError   Severity = "error"
+	SeverityWarning Severity = "warning"
+)
+
+// Code is a stable, machine-readable diagnostic classification.
+type Code string
+
+const (
+	CodeSourceInvalid       Code = "source.invalid"
+	CodeSourceMissing       Code = "source.missing"
+	CodeSourcePermission    Code = "source.permission"
+	CodeSourceRead          Code = "source.read"
+	CodeSourceNotRegular    Code = "source.not_regular"
+	CodeSourceLimitExceeded Code = "source.limit_exceeded"
+	CodeSourceReaderUsed    Code = "source.reader_used"
+
+	CodeYAMLInvalid           Code = "yaml.invalid"
+	CodeYAMLEmpty             Code = "yaml.empty"
+	CodeYAMLMultipleDocuments Code = "yaml.multiple_documents"
+	CodeYAMLRootType          Code = "yaml.root_type"
+	CodeYAMLDuplicateKey      Code = "yaml.duplicate_key"
+	CodeYAMLTag               Code = "yaml.tag"
+	CodeYAMLAnchor            Code = "yaml.anchor"
+	CodeYAMLAlias             Code = "yaml.alias"
+	CodeYAMLMergeKey          Code = "yaml.merge_key"
+	CodeYAMLScalar            Code = "yaml.scalar"
+	CodeYAMLDepthLimit        Code = "yaml.depth_limit"
+	CodeYAMLNodeLimit         Code = "yaml.node_limit"
+
+	CodeSchemaRoot            Code = "schema.root"
+	CodeSchemaUnsupportedType Code = "schema.unsupported_type"
+	CodeSchemaAmbiguousField  Code = "schema.ambiguous_field"
+	CodeSchemaTag             Code = "schema.tag"
+	CodeSchemaTextCodec       Code = "schema.text_codec"
+	CodeSchemaInline          Code = "schema.inline"
+	CodeSchemaCycle           Code = "schema.cycle"
+	CodeSchemaProjectionLimit Code = "schema.projection_limit"
+	CodeSchemaCodec           Code = "schema.codec"
+	CodeSchemaNonFinite       Code = "schema.non_finite"
+	CodeSchemaDynamicType     Code = "schema.dynamic_type"
+
+	CodeDecodeType         Code = "decode.type"
+	CodeDecodeNull         Code = "decode.null"
+	CodeDecodeRange        Code = "decode.range"
+	CodeDecodeDuration     Code = "decode.duration"
+	CodeDecodeText         Code = "decode.text"
+	CodeDecodeUnknownField Code = "decode.unknown_field"
+	CodeDecodeArrayLength  Code = "decode.array_length"
+
+	CodeOptionsInvalid     Code = "options.invalid"
+	CodeOptionsUnavailable Code = "options.unavailable"
+
+	CodeImportDisabled      Code = "import.disabled"
+	CodeImportInvalid       Code = "import.invalid"
+	CodeImportMissing       Code = "import.missing"
+	CodeImportPermission    Code = "import.permission"
+	CodeImportRead          Code = "import.read"
+	CodeImportOutsideRoot   Code = "import.outside_root"
+	CodeImportCycle         Code = "import.cycle"
+	CodeImportRepeated      Code = "import.repeated"
+	CodeImportLimitExceeded Code = "import.limit_exceeded"
+	CodeImportVersion       Code = "import.version"
+
+	CodeOverlayInvalid       Code = "overlay.invalid"
+	CodeOverlayMissing       Code = "overlay.missing"
+	CodeOverlayOutsideRoot   Code = "overlay.outside_root"
+	CodeOverlayRepeated      Code = "overlay.repeated"
+	CodeOverlayDirective     Code = "overlay.directive"
+	CodeOverlayVersion       Code = "overlay.version"
+	CodeOverlayLimitExceeded Code = "overlay.limit_exceeded"
+
+	CodeComposeInvalid  Code = "compose.invalid"
+	CodeComposeConflict Code = "compose.conflict"
+
+	CodeVersionType       Code = "version.type"
+	CodeVersionError      Code = "version.error"
+	CodeVersionWarning    Code = "version.warning"
+	CodeVersionHookFailed Code = "version.hook_failed"
+
+	CodeResolveError            Code = "resolve.error"
+	CodeResolveWarning          Code = "resolve.warning"
+	CodeResolveHookFailed       Code = "resolve.hook_failed"
+	CodeResolveInvalidPath      Code = "resolve.invalid_path"
+	CodeResolveInvalidKind      Code = "resolve.invalid_kind"
+	CodeResolveInvalidRecord    Code = "resolve.invalid_record"
+	CodeResolveInvalidTarget    Code = "resolve.invalid_target"
+	CodeResolveInvalidValue     Code = "resolve.invalid_value"
+	CodeResolveUnrecordedChange Code = "resolve.unrecorded_change"
+
+	CodeValidateError       Code = "validate.error"
+	CodeValidateWarning     Code = "validate.warning"
+	CodeValidateInvalidPath Code = "validate.invalid_path"
+	CodeValidateMutation    Code = "validate.mutation"
+
+	CodeSecretsInvalidPath   Code = "secrets.invalid_path"
+	CodeSecretsMissing       Code = "secrets.missing"
+	CodeSecretsPermission    Code = "secrets.permission"
+	CodeSecretsRead          Code = "secrets.read"
+	CodeSecretsNotRegular    Code = "secrets.not_regular"
+	CodeSecretsInvalidName   Code = "secrets.invalid_name"
+	CodeSecretsLimitExceeded Code = "secrets.limit_exceeded"
+	CodeSecretsInvalidValue  Code = "secrets.invalid_value"
+	CodeSecretsApplyFailed   Code = "secrets.apply_failed"
+
+	CodeSecretRequired    Code = "secret.required"
+	CodeSecretInvalidName Code = "secret.invalid_name"
+	CodeSecretUnset       Code = "secret.unset"
+	CodeSecretEmpty       Code = "secret.empty"
+
+	CodeOverrideInvalidPath   Code = "override.invalid_path"
+	CodeOverrideInvalidLabel  Code = "override.invalid_label"
+	CodeOverrideInvalidValue  Code = "override.invalid_value"
+	CodeOverrideDuplicate     Code = "override.duplicate"
+	CodeOverrideOverlap       Code = "override.overlap"
+	CodeOverrideDirective     Code = "override.directive"
+	CodeOverrideVersion       Code = "override.version"
+	CodeOverrideLimitExceeded Code = "override.limit_exceeded"
+
+	CodeExplainLimitExceeded Code = "explain.limit_exceeded"
+)
+
+// Location identifies a position in a configuration source. Zero line and column
+// values mean that coordinates are unavailable or synthetic.
+type Location struct {
+	SourceID string
+	Line     int
+	Column   int
+}
+
+// SourceInfo describes a source discovered during a load. Path is a canonical
+// local path when one exists. ImportedFrom identifies the declaration that
+// included this source.
+type SourceInfo struct {
+	ID           string
+	Label        string
+	Path         string
+	Layer        Layer
+	ImportedFrom *Location
+}
+
+// Diagnostic is a safe structured problem report. Message and source labels must
+// never contain configuration values or other secrets.
+type Diagnostic struct {
+	Code     Code
+	Severity Severity
+	Path     Path
+	Message  string
+	Primary  *Location
+	Related  []Location
+}
+
+// Origin describes where an effective definition came from. Multiple locations
+// represent a composite origin; resolution origins are synthetic and identify their
+// operation instead of a file location.
+type Origin struct {
+	Layer     Layer
+	Locations []Location
+	Operation ChangeKind
+}
+
+// FieldInfo describes an effective configuration path.
+type FieldInfo struct {
+	Explicit bool
+	Null     bool
+	Origin   Origin
+}
+
+// Change describes a definition or application-resolution operation. Path can name
+// an ancestor operation affecting the queried descendant. Historical values are
+// intentionally not exposed by this record.
+type Change struct {
+	Path         Path
+	Origin       Origin
+	Previous     []Origin
+	Reasons      []string
+	Dependencies []Path
+}
+
+func cloneLocation(location *Location) *Location {
+	if location == nil {
+		return nil
+	}
+	cloned := *location
+	return &cloned
+}
+
+func cloneLocations(locations []Location) []Location {
+	if locations == nil {
+		return nil
+	}
+	return append([]Location(nil), locations...)
+}
+
+func cloneSourceInfo(source SourceInfo) SourceInfo {
+	source.ImportedFrom = cloneLocation(source.ImportedFrom)
+	return source
+}
+
+func cloneSourceInfos(sources []SourceInfo) []SourceInfo {
+	if sources == nil {
+		return nil
+	}
+	cloned := make([]SourceInfo, len(sources))
+	for i, source := range sources {
+		cloned[i] = cloneSourceInfo(source)
+	}
+	return cloned
+}
+
+func cloneOrigin(origin Origin) Origin {
+	origin.Locations = cloneLocations(origin.Locations)
+	return origin
+}
+
+func cloneFieldInfo(info FieldInfo) FieldInfo {
+	info.Origin = cloneOrigin(info.Origin)
+	return info
+}
+
+func cloneChange(change Change) Change {
+	change.Path = change.Path.clone()
+	change.Origin = cloneOrigin(change.Origin)
+	if change.Previous != nil {
+		previous := make([]Origin, len(change.Previous))
+		for i, origin := range change.Previous {
+			previous[i] = cloneOrigin(origin)
+		}
+		change.Previous = previous
+	}
+	change.Reasons = append([]string(nil), change.Reasons...)
+	if change.Dependencies != nil {
+		dependencies := make([]Path, len(change.Dependencies))
+		for i, path := range change.Dependencies {
+			dependencies[i] = path.clone()
+		}
+		change.Dependencies = dependencies
+	}
+	return change
+}
+
+func cloneDiagnostic(diagnostic Diagnostic) Diagnostic {
+	diagnostic.Path = diagnostic.Path.clone()
+	diagnostic.Primary = cloneLocation(diagnostic.Primary)
+	diagnostic.Related = cloneLocations(diagnostic.Related)
+	return diagnostic
+}
+
+func cloneDiagnostics(diagnostics []Diagnostic) []Diagnostic {
+	if diagnostics == nil {
+		return nil
+	}
+	cloned := make([]Diagnostic, len(diagnostics))
+	for i, diagnostic := range diagnostics {
+		cloned[i] = cloneDiagnostic(diagnostic)
+	}
+	return cloned
+}

internal/engine/render.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -14,7 +14,7 @@ var errEffectiveUnavailable = errors.New("configkit: effective configuration is
 // 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 {
+func (r *Inspection) WriteEffective(output io.Writer) error {
 	if r == nil || r.final == nil || output == nil {
 		return errEffectiveUnavailable
 	}

internal/engine/render_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"
@@ -71,7 +71,7 @@ empty_sequence: []
 labels: {hidden: DYNAMIC_CANARY_6a12, public: visible}
 sequence: [second, first]
 `)
-	writeImportFile(t, directory, "profiles/testing.yml", "dynamic: selected\n")
+	writeImportFile(t, directory, "overlays/testing.yml", "dynamic: selected\n")
 	definition := Definition[renderConfig]{
 		Secret: func(path Path) bool {
 			return path.String() == "/labels/hidden" || path.String() == "/dynamic/retired"
@@ -85,7 +85,7 @@ sequence: [second, first]
 			return nil
 		},
 	}
-	result, err := Load[renderConfig](File(mainPath), Options[renderConfig]{Definition: definition, Profile: "testing"})
+	result, err := testLoad[renderConfig](File(mainPath), Options[renderConfig]{Definition: definition, Overlay: "testing"})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -139,7 +139,7 @@ sequence: [second, first]
 	if err := result.WriteEffective(shortWriter{}); !errors.Is(err, io.ErrShortWrite) {
 		t.Fatalf("short writer error = %v", err)
 	}
-	var nilResult *Result[renderConfig]
+	var nilResult *testResult[renderConfig]
 	if err := nilResult.WriteEffective(io.Discard); !errors.Is(err, errEffectiveUnavailable) {
 		t.Fatalf("nil result error = %v", err)
 	}
@@ -160,7 +160,7 @@ func TestSecretValuesStayOutOfLoadFailuresAndWarnings(t *testing.T) {
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			test.definition.Secret = func(path Path) bool { return path.String() == "/credentials" }
-			result, err := Load[renderConfig](Bytes("secret-failure.yml", []byte(test.input)), Options[renderConfig]{Definition: test.definition})
+			result, err := testLoad[renderConfig](Bytes("secret-failure.yml", []byte(test.input)), Options[renderConfig]{Definition: test.definition})
 			if result != nil || err == nil {
 				t.Fatalf("result, error = %#v, %v", result, err)
 			}
@@ -205,7 +205,7 @@ func TestDynamicConcreteTagsRemainSecretThroughHistory(t *testing.T) {
 				Normalize(r, Keys("derived"), &c.Derived, canary, "derive", path)
 				return nil
 			}
-			result, err := Load(NoSource(), Options[cfg]{Definition: definition})
+			result, err := testLoad(NoSource(), Options[cfg]{Definition: definition})
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -234,7 +234,7 @@ func TestValidatorCannotChangeDynamicSensitivityWithoutChangingText(t *testing.T
 	type cfg struct {
 		Payload any `yaml:"payload"`
 	}
-	_, err := Load(Bytes("base", []byte("payload: {token: disposable}\n")), Options[cfg]{Definition: Definition[cfg]{Validate: func(c *cfg, v *Validation) {
+	_, err := testLoad(Bytes("base", []byte("payload: {token: disposable}\n")), Options[cfg]{Definition: Definition[cfg]{Validate: func(c *cfg, v *Validation) {
 		c.Payload = sensitive{Token: c.Payload.(map[string]any)["token"].(string)}
 	}}})
 	var failure *LoadError

internal/engine/resolution.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"reflect"
@@ -15,6 +15,7 @@ type resolutionState struct {
 	schema      *schemaDescriptor
 	presence    map[string]inputPresence
 	document    *document.Node
+	input       resolutionInput
 	records     map[string]*resolutionRecord
 	diagnostics []Diagnostic
 }
@@ -50,6 +51,27 @@ func (r *Resolution) IsExplicit(path Path) bool {
 	return explicit
 }
 
+// InputInfo returns detached entry-state metadata for path. The entry state is
+// the decoded configuration, including retained static defaults, immediately
+// before resolution starts. It is fixed while resolution records mutate the
+// working configuration; unknown or shape-mismatched paths return false.
+//
+// InputInfo is valid only during the resolution callback. See the configuration
+// contract for source and provenance semantics.
+func (r *Resolution) InputInfo(path Path) (FieldInfo, bool) {
+	return r.activeState().input.lookup(path)
+}
+
+// Source returns a detached record for a source acquired by this load. Empty or
+// unknown IDs return false and do not perform input, filesystem, or credential
+// access. A source path is present only when that acquired source has one.
+//
+// Source is valid only during the resolution callback. See the configuration
+// contract for source and provenance semantics.
+func (r *Resolution) Source(id string) (SourceInfo, bool) {
+	return r.activeState().input.source(id)
+}
+
 // Record declares the intent for a resolver mutation. A container path covers
 // mutations to its descendants.
 func (r *Resolution) Record(path Path, kind ChangeKind, reason string, dependencies ...Path) {
@@ -221,9 +243,10 @@ func (state *resolutionState) addDiagnostic(code Code, path Path, message string
 	state.diagnostics = append(state.diagnostics, diagnostic)
 }
 
-func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error, schema *schemaDescriptor, decoded decodedConfiguration, input *document.Node) resolutionResult {
+func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error, schema *schemaDescriptor, decoded decodedConfiguration, input *document.Node, entry resolutionInput) resolutionResult {
 	state := &resolutionState{
 		active: true, schema: schema, presence: decoded.presence, document: input,
+		input:   entry,
 		records: make(map[string]*resolutionRecord),
 	}
 	context := &Resolution{state: state}

internal/engine/resolution_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -41,7 +41,7 @@ func TestLoadRunsRecordedResolutionWithMapWriteback(t *testing.T) {
 		},
 	}
 	input := "poll_interval: 1m\nartifacts:\n  second: {output: ' second '}\n  first: {output: ' first '}\n"
-	result, err := Load(Bytes("resolution.yml", []byte(input)), Options[config]{Definition: definition})
+	result, err := testLoad(Bytes("resolution.yml", []byte(input)), Options[config]{Definition: definition})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -94,7 +94,7 @@ func TestResolutionPreservesExplicitNullAndZeroWhileReplacingAbsentBaseline(t *t
 		Absent   int  `yaml:"absent"`
 	}
 	five := 5
-	result, err := Load(Bytes("explicit.yml", []byte("optional: null\ncount: 0\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("explicit.yml", []byte("optional: null\ncount: 0\n")), Options[config]{Definition: Definition[config]{
 		Defaults: func() config { return config{Optional: &five, Count: 5, Absent: 5} },
 		Resolve: func(configuration *config, resolution *Resolution) error {
 			if !resolution.IsExplicit(Keys("optional")) || !resolution.IsExplicit(Keys("count")) || resolution.IsExplicit(Keys("absent")) {
@@ -126,7 +126,7 @@ func TestResolutionCoalescesEqualAndRepeatedHelperIntent(t *testing.T) {
 		Value int `yaml:"value"`
 		Other int `yaml:"other"`
 	}
-	result, err := Load(NoSource(), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(NoSource(), Options[config]{Definition: Definition[config]{
 		Defaults: func() config { return config{Value: 5} },
 		Resolve: func(configuration *config, resolution *Resolution) error {
 			Default(resolution, Keys("value"), &configuration.Value, 5, "equal derived intent", Keys("other"))
@@ -157,7 +157,7 @@ func TestResolutionContainerRecordCoversSubtreeRemovalAndSnapshotsAreDetached(t
 	type config struct {
 		Items map[string]item `yaml:"items"`
 	}
-	result, err := Load(Bytes("remove.yml", []byte("items:\n  keep: {value: 'yes'}\n  remove: {value: 'no'}\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("remove.yml", []byte("items:\n  keep: {value: 'yes'}\n  remove: {value: 'no'}\n")), Options[config]{Definition: Definition[config]{
 		Resolve: func(configuration *config, resolution *Resolution) error {
 			delete(configuration.Items, "remove")
 			resolution.Record(Keys("items"), ChangeNormalization, "removed disabled entries")
@@ -188,7 +188,7 @@ func TestResolutionSequenceReplacementUpdatesDescendantOrigins(t *testing.T) {
 	type config struct {
 		Values []int `yaml:"values"`
 	}
-	result, err := Load(Bytes("sequence.yml", []byte("values: [1, 2]\n")), Options[config]{Definition: Definition[config]{
+	result, err := testLoad(Bytes("sequence.yml", []byte("values: [1, 2]\n")), Options[config]{Definition: Definition[config]{
 		Resolve: func(configuration *config, resolution *Resolution) error {
 			Normalize(resolution, Keys("values"), &configuration.Values, []int{3}, "replaced values")
 			return nil
@@ -237,7 +237,7 @@ func TestResolutionRejectsUnrecordedAndMismatchedMutations(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			result, err := Load(Bytes("invalid-resolution.yml", []byte("value: 1\n")), Options[config]{Definition: Definition[config]{Resolve: test.resolve}})
+			result, err := testLoad(Bytes("invalid-resolution.yml", []byte("value: 1\n")), Options[config]{Definition: Definition[config]{Resolve: test.resolve}})
 			assertLoadDiagnostic(t, result, err, test.code)
 		})
 	}
@@ -269,7 +269,7 @@ func TestResolutionRejectsInvalidProjectedValuesAndSuppressesReturnedErrors(t *t
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			result, err := Load(Bytes("resolution-errors.yml", []byte("value: 1\nnumber: 1\n")), Options[config]{Definition: Definition[config]{Resolve: test.resolve}})
+			result, err := testLoad(Bytes("resolution-errors.yml", []byte("value: 1\nnumber: 1\n")), Options[config]{Definition: Definition[config]{Resolve: test.resolve}})
 			loadError := assertLoadDiagnostic(t, result, err, test.code)
 			for _, diagnostic := range loadError.Diagnostics() {
 				if strings.Contains(diagnostic.Message, "CANARY") {
@@ -280,6 +280,83 @@ func TestResolutionRejectsInvalidProjectedValuesAndSuppressesReturnedErrors(t *t
 	}
 }
 
+func TestResolutionEntryQueriesExposeDetachedLoadInput(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Declared string  `yaml:"declared"`
+		Default  string  `yaml:"default"`
+		Optional *string `yaml:"optional"`
+	}
+	filename := writeImportFile(t, t.TempDir(), "config.yml", "declared: file\noptional: null\n")
+	var savedField FieldInfo
+	var savedSource SourceInfo
+	result, err := testLoad[config](File(filename), Options[config]{Definition: Definition[config]{
+		Defaults: func() config { return config{Default: "retained"} },
+		Resolve: func(_ *config, resolution *Resolution) error {
+			for _, path := range []Path{Keys("declared"), Keys("default"), Keys("optional")} {
+				info, found := resolution.InputInfo(path)
+				if !found || info.Explicit != resolution.IsExplicit(path) {
+					return errors.New("entry metadata does not agree with explicitness")
+				}
+			}
+			defaultInfo, _ := resolution.InputInfo(Keys("default"))
+			optionalInfo, _ := resolution.InputInfo(Keys("optional"))
+			if defaultInfo.Explicit || defaultInfo.Origin.Layer != LayerDefault || !optionalInfo.Explicit || !optionalInfo.Null {
+				return errors.New("entry metadata lost default or null state")
+			}
+			if _, found := resolution.InputInfo(Keys("missing")); found {
+				return errors.New("missing entry path was found")
+			}
+			declared, _ := resolution.InputInfo(Keys("declared"))
+			if len(declared.Origin.Locations) != 1 {
+				return errors.New("declared source location is missing")
+			}
+			source, found := resolution.Source(declared.Origin.Locations[0].SourceID)
+			if !found || source.Path != canonicalTestPath(t, filename) || source.ID != "source-1" {
+				return errors.New("declared source record is missing")
+			}
+			if _, found := resolution.Source(""); found {
+				return errors.New("empty source identity was found")
+			}
+			if _, found := resolution.Source("unknown"); found {
+				return errors.New("unknown source identity was found")
+			}
+			savedField, savedSource = declared, source
+			return nil
+		},
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Config.Declared != "file" || result.Config.Default != "retained" || result.Config.Optional != nil {
+		t.Fatalf("configuration = %#v", result.Config)
+	}
+	savedField.Origin.Locations[0].SourceID = "mutated"
+	savedSource.Label = "mutated"
+	field, _ := result.Metadata().Lookup(Keys("declared"))
+	if field.Origin.Locations[0].SourceID != "source-1" || result.Sources()[0].Label == "mutated" {
+		t.Fatal("saved resolution records alias a completed result")
+	}
+
+	noSource, err := testLoad[config](NoSource(), Options[config]{Definition: Definition[config]{
+		Defaults: func() config { return config{Default: "retained"} },
+		Resolve: func(_ *config, resolution *Resolution) error {
+			info, found := resolution.InputInfo(Keys("default"))
+			if !found || info.Explicit || resolution.IsExplicit(Keys("default")) {
+				return errors.New("defaults-only entry metadata is wrong")
+			}
+			if _, found := resolution.Source("source-1"); found {
+				return errors.New("defaults-only load invented a source")
+			}
+			return nil
+		},
+	}})
+	if err != nil || noSource.Config.Default != "retained" {
+		t.Fatalf("defaults-only load = %#v, %v", noSource, err)
+	}
+}
+
 func TestResolutionContextPanicsAfterCallback(t *testing.T) {
 	t.Parallel()
 
@@ -287,7 +364,7 @@ func TestResolutionContextPanicsAfterCallback(t *testing.T) {
 		Value int `yaml:"value"`
 	}
 	var retained *Resolution
-	if _, err := Load(NoSource(), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+	if _, err := testLoad(NoSource(), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
 		retained = resolution
 		return nil
 	}}}); err != nil {
@@ -301,6 +378,45 @@ func TestResolutionContextPanicsAfterCallback(t *testing.T) {
 	retained.IsExplicit(Keys("value"))
 }
 
+func TestResolutionEntryQueriesRequireAnActiveCallback(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Value int `yaml:"value"`
+	}
+	requireClosed := func(t *testing.T, call func()) {
+		t.Helper()
+		defer func() {
+			if recovered := recover(); recovered != closedCallbackContextMessage {
+				t.Fatalf("panic = %#v", recovered)
+			}
+		}()
+		call()
+	}
+	requireClosed(t, func() { (*Resolution)(nil).InputInfo(Keys("value")) })
+	requireClosed(t, func() { (&Resolution{}).Source("source-1") })
+
+	var successful *Resolution
+	if _, err := testLoad(NoSource(), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+		successful = resolution
+		return nil
+	}}}); err != nil {
+		t.Fatal(err)
+	}
+	requireClosed(t, func() { successful.InputInfo(Keys("value")) })
+	requireClosed(t, func() { successful.Source("source-1") })
+
+	var failed *Resolution
+	if _, err := testLoad(NoSource(), Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+		failed = resolution
+		return errors.New("resolver failed")
+	}}}); err == nil {
+		t.Fatal("failed resolver succeeded")
+	}
+	requireClosed(t, func() { failed.InputInfo(Keys("value")) })
+	requireClosed(t, func() { failed.Source("source-1") })
+}
+
 func TestValidationContextPanicsAfterVersionCallback(t *testing.T) {
 	t.Parallel()
 
@@ -308,7 +424,7 @@ func TestValidationContextPanicsAfterVersionCallback(t *testing.T) {
 		Version string `yaml:"version"`
 	}
 	var retained *Validation
-	if _, err := Load(Bytes("version-context.yml", []byte("version: one\n")), Options[config]{Definition: Definition[config]{
+	if _, err := testLoad(Bytes("version-context.yml", []byte("version: one\n")), Options[config]{Definition: Definition[config]{
 		Version: &VersionRule{Path: Keys("version"), Check: func(_ Version, validation *Validation) error {
 			retained = validation
 			return nil
@@ -324,7 +440,7 @@ func TestValidationContextPanicsAfterVersionCallback(t *testing.T) {
 	retained.Warning(Keys("version"), "too late")
 }
 
-func assertLoadDiagnostic[T any](t *testing.T, result *Result[T], err error, code Code) *LoadError {
+func assertLoadDiagnostic[T any](t *testing.T, result *testResult[T], err error, code Code) *LoadError {
 	t.Helper()
 	if result != nil || err == nil {
 		t.Fatalf("result, err = %#v, %v", result, err)

internal/engine/schema.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"encoding"
@@ -29,8 +29,9 @@ const (
 )
 
 type schemaDescriptor struct {
-	root  *typeDescriptor
-	types map[reflect.Type]*typeDescriptor
+	root    *typeDescriptor
+	types   map[reflect.Type]*typeDescriptor
+	secrets SecretBinding
 }
 
 type typeDescriptor struct {
@@ -65,20 +66,39 @@ type schemaIssue struct {
 	message string
 }
 
+// SecretState is the private operation state for one exact-type secret value.
+// It is supplied by the facade and never enters inspection records.
+type SecretState struct {
+	Name      string
+	Value     string
+	Specified bool
+	Resolved  bool
+}
+
+// SecretBinding adapts the facade-owned exact secret type for one load.
+// Bindings are operation data: callers must supply the type and conversions
+// together, and a binding never becomes package-global state.
+type SecretBinding struct {
+	Type reflect.Type
+	Read func(reflect.Value) SecretState
+	Make func(SecretState) reflect.Value
+}
+
 var (
 	durationType        = reflect.TypeFor[time.Duration]()
-	secretType          = reflect.TypeFor[Secret]()
 	textMarshalerType   = reflect.TypeFor[encoding.TextMarshaler]()
 	textUnmarshalerType = reflect.TypeFor[encoding.TextUnmarshaler]()
 )
 
-func buildSchema(root reflect.Type) (*schemaDescriptor, *schemaIssue) {
+func buildSchema(root reflect.Type, secrets SecretBinding) (*schemaDescriptor, *schemaIssue) {
+	secrets.validate()
 	if root == nil || (root.Kind() != reflect.Struct && !isStringMap(root)) {
 		return nil, &schemaIssue{code: CodeSchemaRoot, message: "configuration root must be a struct or string-keyed map"}
 	}
 	builder := schemaBuilder{
 		cache:    make(map[reflect.Type]*typeDescriptor),
 		building: make(map[reflect.Type]bool),
+		secrets:  secrets,
 	}
 	descriptor, issue := builder.describe(root, Path{})
 	if issue != nil {
@@ -87,12 +107,13 @@ func buildSchema(root reflect.Type) (*schemaDescriptor, *schemaIssue) {
 	if descriptor.kind != descriptorStruct && descriptor.kind != descriptorMap {
 		return nil, &schemaIssue{code: CodeSchemaRoot, message: "configuration root must be a structural struct or string-keyed map"}
 	}
-	return &schemaDescriptor{root: descriptor, types: builder.cache}, nil
+	return &schemaDescriptor{root: descriptor, types: builder.cache, secrets: secrets}, nil
 }
 
 type schemaBuilder struct {
 	cache    map[reflect.Type]*typeDescriptor
 	building map[reflect.Type]bool
+	secrets  SecretBinding
 }
 
 func (b *schemaBuilder) describe(current reflect.Type, path Path) (*typeDescriptor, *schemaIssue) {
@@ -122,7 +143,7 @@ func (b *schemaBuilder) describe(current reflect.Type, path Path) (*typeDescript
 		descriptor.kind = descriptorDuration
 		return descriptor, nil
 	}
-	if current == secretType {
+	if b.secrets.Type != nil && current == b.secrets.Type {
 		descriptor.kind = descriptorSecret
 		return descriptor, nil
 	}
@@ -189,6 +210,15 @@ func (b *schemaBuilder) describe(current reflect.Type, path Path) (*typeDescript
 	return descriptor, nil
 }
 
+func (binding SecretBinding) validate() {
+	if binding.Type == nil {
+		return
+	}
+	if binding.Read == nil || binding.Make == nil {
+		panic("configkit engine: incomplete secret binding")
+	}
+}
+
 func (b *schemaBuilder) describeFields(descriptor *typeDescriptor, current reflect.Type, path Path) *schemaIssue {
 	for i := 0; i < current.NumField(); i++ {
 		field := current.Field(i)

internal/engine/schema_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -68,9 +68,9 @@ func TestBuildSchemaDescribesSupportedTypes(t *testing.T) {
 		private       chan int
 	}
 
-	schema, issue := buildSchema(reflect.TypeFor[config]())
+	schema, issue := testBuildSchema(reflect.TypeFor[config]())
 	if issue != nil {
-		t.Fatalf("buildSchema() issue = %#v", issue)
+		t.Fatalf("testBuildSchema() issue = %#v", issue)
 	}
 	root := schema.root
 	checks := map[string]descriptorKind{
@@ -105,7 +105,7 @@ func TestBuildSchemaDescribesSupportedTypes(t *testing.T) {
 	if root.inlineMap == nil || root.inlineMap.descriptor.kind != descriptorMap {
 		t.Fatalf("inline map = %#v", root.inlineMap)
 	}
-	if mapped, mapIssue := buildSchema(reflect.TypeFor[map[string]nested]()); mapIssue != nil || mapped.root.kind != descriptorMap {
+	if mapped, mapIssue := testBuildSchema(reflect.TypeFor[map[string]nested]()); mapIssue != nil || mapped.root.kind != descriptorMap {
 		t.Fatalf("string-keyed root map = %#v, issue=%#v", mapped, mapIssue)
 	}
 	if _, exists := root.fieldByName["ignored"]; exists {
@@ -116,7 +116,7 @@ func TestBuildSchemaDescribesSupportedTypes(t *testing.T) {
 func TestBuildSchemaSupportsRecursiveDescriptorsWithoutSharingLoads(t *testing.T) {
 	t.Parallel()
 
-	first, issue := buildSchema(reflect.TypeFor[recursiveConfig]())
+	first, issue := testBuildSchema(reflect.TypeFor[recursiveConfig]())
 	if issue != nil {
 		t.Fatal(issue.message)
 	}
@@ -128,7 +128,7 @@ func TestBuildSchemaSupportsRecursiveDescriptorsWithoutSharingLoads(t *testing.T
 	if children.kind != descriptorMap || children.element != first.root {
 		t.Fatal("recursive map did not refer to the existing descriptor")
 	}
-	second, issue := buildSchema(reflect.TypeFor[recursiveConfig]())
+	second, issue := testBuildSchema(reflect.TypeFor[recursiveConfig]())
 	if issue != nil {
 		t.Fatal(issue.message)
 	}
@@ -207,7 +207,7 @@ func TestBuildSchemaRejectsInvalidRootsTypesTagsAndBindings(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			if _, issue := buildSchema(test.typeOf); issue == nil || issue.code != test.code {
+			if _, issue := testBuildSchema(test.typeOf); issue == nil || issue.code != test.code {
 				t.Fatalf("issue = %#v, want %s", issue, test.code)
 			}
 		})
@@ -221,7 +221,7 @@ func TestBuildSchemaDoesNotExecuteApplicationMethods(t *testing.T) {
 		Value      panicText      `yaml:"value"`
 		Structural yamlHookStruct `yaml:"structural"`
 	}
-	if _, issue := buildSchema(reflect.TypeFor[config]()); issue != nil {
+	if _, issue := testBuildSchema(reflect.TypeFor[config]()); issue != nil {
 		t.Fatal(issue.message)
 	}
 }
@@ -261,7 +261,7 @@ func TestResolveSchemaPathUsesContainerSemantics(t *testing.T) {
 		Dynamic any               `yaml:"dynamic"`
 		Extras  map[string]string `yaml:",inline"`
 	}
-	schema, issue := buildSchema(reflect.TypeFor[config]())
+	schema, issue := testBuildSchema(reflect.TypeFor[config]())
 	if issue != nil {
 		t.Fatal(issue.message)
 	}
@@ -310,7 +310,7 @@ func TestInlineMapPointersFailBeforeDefaults(t *testing.T) {
 	}
 	for _, nonNil := range []bool{false, true} {
 		called := false
-		_, err := Load(NoSource(), Options[cfg]{Definition: Definition[cfg]{Defaults: func() cfg {
+		_, err := testLoad(NoSource(), Options[cfg]{Definition: Definition[cfg]{Defaults: func() cfg {
 			called = true
 			if nonNil {
 				m := map[string]int{"value": 1}
@@ -330,13 +330,13 @@ func TestInlineMapPointersFailBeforeDefaults(t *testing.T) {
 	type recursive struct {
 		Extra pointer `yaml:",inline"`
 	}
-	if _, err := Load[recursive](NoSource()); err == nil {
+	if _, err := testLoad[recursive](NoSource()); err == nil {
 		t.Fatal("recursive inline pointer was accepted")
 	}
 	type double struct {
 		Extra **map[string]int `yaml:",inline"`
 	}
-	if _, err := Load[double](NoSource()); err == nil {
+	if _, err := testLoad[double](NoSource()); err == nil {
 		t.Fatal("double inline map pointer was accepted")
 	}
 }

internal/engine/secret.go

@@ -0,0 +1,153 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+type secretDependency struct {
+	target     Path
+	dependency Path
+}
+
+func classifySecretPaths(schema *schemaDescriptor, predicate func(Path) bool, metadata Metadata, final *document.Node, applications []historyApplication, projections ...*document.Node) map[string]bool {
+	paths := make(map[string]Path)
+	finalPaths := make(map[string]*document.Node)
+	indexDocument(final, Path{}, finalPaths)
+	for pointer := range finalPaths {
+		addSecretPath(paths, pointer)
+	}
+	for _, application := range applications {
+		applicationPaths := make(map[string]*document.Node)
+		indexDocument(application.value, application.path, applicationPaths)
+		for pointer := range applicationPaths {
+			addSecretPath(paths, pointer)
+		}
+	}
+	var dependencies []secretDependency
+	for pointer, history := range metadata.history {
+		addSecretPath(paths, pointer)
+		for _, change := range history {
+			paths[change.Path.String()] = change.Path.clone()
+			for _, dependency := range change.Dependencies {
+				paths[dependency.String()] = dependency.clone()
+				dependencies = append(dependencies, secretDependency{
+					target: change.Path.clone(), dependency: dependency.clone(),
+				})
+			}
+		}
+	}
+
+	secret := make(map[string]bool)
+	for _, tree := range append(projections, final) {
+		projected := make(map[string]*document.Node)
+		indexDocument(tree, Path{}, projected)
+		for pointer, node := range projected {
+			addSecretPath(paths, pointer)
+			if node.Sensitive {
+				secret[pointer] = true
+			}
+		}
+	}
+	for pointer, path := range paths {
+		if root, ok := schemaSecretRoot(schema, path); ok {
+			secret[root.String()] = true
+		}
+		if predicate != nil && predicate(path.clone()) {
+			secret[pointer] = true
+		}
+	}
+	for {
+		changed := false
+		for _, dependency := range dependencies {
+			if secretIntersectsPath(paths, secret, dependency.dependency) && !secret[dependency.target.String()] {
+				secret[dependency.target.String()] = true
+				changed = true
+			}
+		}
+		if !changed {
+			return secret
+		}
+	}
+}
+
+func addSecretPath(paths map[string]Path, pointer string) {
+	if path, err := ParsePath(pointer); err == nil {
+		paths[pointer] = path
+	}
+}
+
+func secretIntersectsPath(paths map[string]Path, secret map[string]bool, candidate Path) bool {
+	for pointer := range secret {
+		classified, ok := paths[pointer]
+		if !ok {
+			continue
+		}
+		if pathContains(classified, candidate) || pathContains(candidate, classified) {
+			return true
+		}
+	}
+	return false
+}
+
+func schemaSecretRoot(schema *schemaDescriptor, path Path) (Path, bool) {
+	if schema == nil || schema.root == nil || !path.valid() {
+		return Path{}, false
+	}
+	current := schema.root
+	walked := Path{}
+	for _, segment := range path.segments {
+		walked.segments = append(walked.segments, segment)
+		for current.kind == descriptorPointer {
+			current = current.element
+		}
+		switch current.kind {
+		case descriptorStruct:
+			if segment.kind == pathSegmentIndex {
+				return Path{}, false
+			}
+			position, ok := current.fieldByName[segment.key]
+			var field *fieldDescriptor
+			if ok {
+				field = &current.fields[position]
+			} else {
+				field = current.inlineMap
+			}
+			if field == nil {
+				return Path{}, false
+			}
+			if field.secret {
+				return walked.clone(), true
+			}
+			if field.inlineMap {
+				current = field.descriptor.element
+			} else {
+				current = field.descriptor
+			}
+		case descriptorMap:
+			if segment.kind == pathSegmentIndex {
+				return Path{}, false
+			}
+			current = current.element
+		case descriptorSlice, descriptorArray:
+			if _, ok := schemaIndex(segment); !ok {
+				return Path{}, false
+			}
+			current = current.element
+		case descriptorDynamic:
+			return Path{}, false
+		default:
+			return Path{}, false
+		}
+	}
+	return Path{}, false
+}
+
+// Dynamic type replacement can change classification even when projected text
+// is equal. Validators must preserve this inspection metadata as well as values.
+func projectedSensitivity(root *document.Node) map[string]Path {
+	result := make(map[string]Path)
+	walkDocument(root, Path{}, func(path Path, node *document.Node) {
+		if node.Sensitive {
+			result[path.String()] = path.clone()
+		}
+	})
+	return result
+}

internal/engine/secret_binding_test.go

@@ -0,0 +1,157 @@
+package engine
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"reflect"
+	"strconv"
+	"testing"
+)
+
+// Secret is a test-local facade secret. Production engine code must not depend
+// on this type; each test load supplies the binding below explicitly.
+type Secret struct {
+	name      string
+	value     string
+	specified bool
+	resolved  bool
+}
+
+func SecretEnv(name string) Secret {
+	return Secret{name: name, specified: true}
+}
+
+func (s Secret) EnvName() string {
+	return s.name
+}
+
+func (s Secret) Value() string {
+	if !s.resolved {
+		return ""
+	}
+	return s.value
+}
+
+func (s Secret) IsResolved() bool {
+	return s.resolved
+}
+
+func (s Secret) Format(state fmt.State, _ rune) {
+	_, _ = io.WriteString(state, "configkit.SecretEnv("+strconv.Quote(s.name)+")")
+}
+
+func (s Secret) MarshalJSON() ([]byte, error) {
+	return json.Marshal(s.name)
+}
+
+func testSecretBinding() SecretBinding {
+	return SecretBinding{
+		Type: reflect.TypeFor[Secret](),
+		Read: func(value reflect.Value) SecretState {
+			secret := value.Interface().(Secret)
+			return SecretState{Name: secret.name, Value: secret.value, Specified: secret.specified, Resolved: secret.resolved}
+		},
+		Make: func(state SecretState) reflect.Value {
+			return reflect.ValueOf(Secret{name: state.Name, value: state.Value, specified: state.Specified, resolved: state.Resolved})
+		},
+	}
+}
+
+func testLoad[T any](source Source, supplied ...Options[T]) (*testResult[T], error) {
+	loaded, err := Load(source, testSecretBinding(), supplied...)
+	return testLoaded(loaded), err
+}
+
+func testLoadWithSecretLookup[T any](source Source, lookup secretLookup, supplied ...Options[T]) (*testResult[T], error) {
+	loaded, err := loadWithSecretLookup(source, testSecretBinding(), lookup, supplied...)
+	return testLoaded(loaded), err
+}
+
+type testResult[T any] struct {
+	Config T
+	*Inspection
+}
+
+func testLoaded[T any](loaded *Loaded[T]) *testResult[T] {
+	if loaded == nil {
+		return nil
+	}
+	return &testResult[T]{Config: loaded.Config, Inspection: loaded.Inspection}
+}
+func (r *testResult[T]) Metadata() Metadata {
+	if r == nil {
+		return Metadata{}
+	}
+	return r.Inspection.Metadata()
+}
+func (r *testResult[T]) Sources() []SourceInfo {
+	if r == nil {
+		return nil
+	}
+	return r.Inspection.Sources()
+}
+func (r *testResult[T]) Diagnostics() []Diagnostic {
+	if r == nil {
+		return nil
+	}
+	return r.Inspection.Diagnostics()
+}
+func (r *testResult[T]) Explain(path Path) (Explanation, bool) {
+	if r == nil {
+		return Explanation{}, false
+	}
+	return r.Inspection.Explain(path)
+}
+func (r *testResult[T]) WriteEffective(output io.Writer) error {
+	if r == nil {
+		return errEffectiveUnavailable
+	}
+	return r.Inspection.WriteEffective(output)
+}
+func (r *testResult[T]) WriteExplanation(output io.Writer, path Path) error {
+	if r == nil {
+		return errExplanationUnknownPath
+	}
+	return r.Inspection.WriteExplanation(output, path)
+}
+
+func testBuildSchema(root reflect.Type) (*schemaDescriptor, *schemaIssue) {
+	return buildSchema(root, testSecretBinding())
+}
+
+func TestSecretBindingsRemainExactAndIndependent(t *testing.T) {
+	t.Parallel()
+
+	type otherSecret struct {
+		name string
+	}
+	other := SecretBinding{
+		Type: reflect.TypeFor[otherSecret](),
+		Read: func(value reflect.Value) SecretState {
+			return SecretState{Name: value.Interface().(otherSecret).name}
+		},
+		Make: func(state SecretState) reflect.Value {
+			return reflect.ValueOf(otherSecret{name: state.Name})
+		},
+	}
+	type config struct {
+		First  Secret      `yaml:"first"`
+		Second otherSecret `yaml:"second"`
+	}
+	firstSchema, firstIssue := buildSchema(reflect.TypeFor[config](), testSecretBinding())
+	if firstIssue != nil {
+		t.Fatal(firstIssue)
+	}
+	secondSchema, secondIssue := buildSchema(reflect.TypeFor[config](), other)
+	if secondIssue != nil {
+		t.Fatal(secondIssue)
+	}
+	firstField := firstSchema.root.fields[firstSchema.root.fieldByName["first"]].descriptor
+	firstOther := firstSchema.root.fields[firstSchema.root.fieldByName["second"]].descriptor
+	secondField := secondSchema.root.fields[secondSchema.root.fieldByName["first"]].descriptor
+	secondOther := secondSchema.root.fields[secondSchema.root.fieldByName["second"]].descriptor
+	if firstField.kind != descriptorSecret || firstOther.kind == descriptorSecret || secondField.kind == descriptorSecret || secondOther.kind != descriptorSecret {
+		t.Fatalf("secret descriptor kinds = %v, %v, %v, %v", firstField.kind, firstOther.kind, secondField.kind, secondOther.kind)
+	}
+}

internal/engine/secret_reference.go

@@ -1,61 +1,13 @@
-package configkit
+package engine
 
 import (
 	"cmp"
-	"encoding/json"
-	"fmt"
-	"io"
 	"reflect"
 	"slices"
-	"strconv"
 
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 )
 
-// Secret is an opaque reference to an environment variable. Its name is public
-// configuration; its resolved value is available only through Value.
-type Secret struct {
-	name      string
-	value     string
-	specified bool
-	resolved  bool
-}
-
-// SecretEnv constructs an unresolved environment-backed secret reference.
-// Invalid names are reported if the reference survives a configuration load.
-func SecretEnv(name string) Secret {
-	return Secret{name: name, specified: true}
-}
-
-// EnvName returns the public environment-variable name.
-func (s Secret) EnvName() string {
-	return s.name
-}
-
-// Value returns the resolved credential, or an empty string when unresolved.
-func (s Secret) Value() string {
-	if !s.resolved {
-		return ""
-	}
-	return s.value
-}
-
-// IsResolved reports whether this reference resolved to a nonempty value during
-// its configuration load.
-func (s Secret) IsResolved() bool {
-	return s.resolved
-}
-
-// Format renders only the public reference name for every formatting verb.
-func (s Secret) Format(state fmt.State, _ rune) {
-	_, _ = io.WriteString(state, "configkit.SecretEnv("+strconv.Quote(s.name)+")")
-}
-
-// MarshalJSON emits only the public environment-variable name.
-func (s Secret) MarshalJSON() ([]byte, error) {
-	return json.Marshal(s.name)
-}
-
 type secretLookup func(string) (string, bool)
 
 type secretLookupResult struct {
@@ -80,28 +32,28 @@ func resolveSecretReferences(root reflect.Value, schema *schemaDescriptor, input
 	if lookup == nil {
 		lookup = func(string) (string, bool) { return "", false }
 	}
-	resolveSecretValue(root, schema.root, Path{}, false, input, lookup, &result)
+	resolveSecretValue(root, schema.root, schema.secrets, Path{}, false, input, lookup, &result)
 	result.diagnostics = canonicalDiagnostics(result.diagnostics)
 	return result
 }
 
-func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Path, optional bool, input *document.Node, lookup secretLookup, result *secretResolutionResult) {
+func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, secrets SecretBinding, path Path, optional bool, input *document.Node, lookup secretLookup, result *secretResolutionResult) {
 	if descriptor.kind == descriptorPointer {
 		if value.IsNil() {
 			return
 		}
-		resolveSecretValue(value.Elem(), descriptor.element, path, descriptor.element.kind == descriptorSecret, input, lookup, result)
+		resolveSecretValue(value.Elem(), descriptor.element, secrets, path, descriptor.element.kind == descriptorSecret, input, lookup, result)
 		return
 	}
 
 	switch descriptor.kind {
 	case descriptorSecret:
-		reference := value.Interface().(Secret)
-		name := reference.EnvName()
+		reference := secrets.Read(value)
+		name := reference.Name
 		if name == "" {
 			code := CodeSecretRequired
 			message := "required secret reference is absent"
-			if optional || reference.specified {
+			if optional || reference.Specified {
 				code = CodeSecretInvalidName
 				message = "secret environment name is empty"
 			}
@@ -125,7 +77,7 @@ func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Pa
 			result.diagnostics = append(result.diagnostics, secretDiagnostic(CodeSecretEmpty, path, "secret environment variable is empty", input))
 			return
 		}
-		value.Set(reflect.ValueOf(Secret{name: name, value: found.value, specified: true, resolved: true}))
+		value.Set(secrets.Make(SecretState{Name: name, Value: found.value, Specified: true, Resolved: true}))
 		result.references[path.String()] = name
 	case descriptorStruct:
 		for _, member := range descriptor.members {
@@ -133,7 +85,7 @@ func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Pa
 			if !member.inline {
 				memberPath = path.Key(member.name)
 			}
-			resolveSecretValue(value.Field(member.index), member.descriptor, memberPath, false, input, lookup, result)
+			resolveSecretValue(value.Field(member.index), member.descriptor, secrets, memberPath, false, input, lookup, result)
 		}
 	case descriptorMap:
 		if value.IsNil() {
@@ -144,7 +96,7 @@ func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Pa
 		for _, key := range keys {
 			entry := reflect.New(value.Type().Elem()).Elem()
 			entry.Set(value.MapIndex(key))
-			resolveSecretValue(entry, descriptor.element, path.Key(key.String()), false, input, lookup, result)
+			resolveSecretValue(entry, descriptor.element, secrets, path.Key(key.String()), false, input, lookup, result)
 			value.SetMapIndex(key, entry)
 		}
 	case descriptorSlice, descriptorArray:
@@ -152,7 +104,7 @@ func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Pa
 			return
 		}
 		for index := 0; index < value.Len(); index++ {
-			resolveSecretValue(value.Index(index), descriptor.element, path.Index(index), false, input, lookup, result)
+			resolveSecretValue(value.Index(index), descriptor.element, secrets, path.Index(index), false, input, lookup, result)
 		}
 	}
 }
@@ -165,25 +117,28 @@ func secretDiagnostic(code Code, path Path, message string, input *document.Node
 	return diagnostic
 }
 
-func changedSecretStates(root reflect.Value, descriptor *typeDescriptor, lookups map[string]secretLookupResult) []Path {
+func changedSecretStates(root reflect.Value, schema *schemaDescriptor, lookups map[string]secretLookupResult) []Path {
 	var changed []Path
-	collectChangedSecretStates(root, descriptor, Path{}, lookups, &changed)
+	if schema == nil || schema.root == nil {
+		return nil
+	}
+	collectChangedSecretStates(root, schema.root, schema.secrets, Path{}, lookups, &changed)
 	slices.SortFunc(changed, func(left, right Path) int { return cmp.Compare(left.String(), right.String()) })
 	return changed
 }
 
-func collectChangedSecretStates(value reflect.Value, descriptor *typeDescriptor, path Path, lookups map[string]secretLookupResult, changed *[]Path) {
+func collectChangedSecretStates(value reflect.Value, descriptor *typeDescriptor, secrets SecretBinding, path Path, lookups map[string]secretLookupResult, changed *[]Path) {
 	if descriptor.kind == descriptorPointer {
 		if !value.IsNil() {
-			collectChangedSecretStates(value.Elem(), descriptor.element, path, lookups, changed)
+			collectChangedSecretStates(value.Elem(), descriptor.element, secrets, path, lookups, changed)
 		}
 		return
 	}
 	switch descriptor.kind {
 	case descriptorSecret:
-		reference := value.Interface().(Secret)
-		expected, ok := lookups[reference.EnvName()]
-		if ok && (!expected.present || expected.value == "" || !reference.resolved || reference.value != expected.value) {
+		reference := secrets.Read(value)
+		expected, ok := lookups[reference.Name]
+		if ok && (!expected.present || expected.value == "" || !reference.Resolved || reference.Value != expected.value) {
 			*changed = append(*changed, path.clone())
 		}
 	case descriptorStruct:
@@ -192,7 +147,7 @@ func collectChangedSecretStates(value reflect.Value, descriptor *typeDescriptor,
 			if !member.inline {
 				memberPath = path.Key(member.name)
 			}
-			collectChangedSecretStates(value.Field(member.index), member.descriptor, memberPath, lookups, changed)
+			collectChangedSecretStates(value.Field(member.index), member.descriptor, secrets, memberPath, lookups, changed)
 		}
 	case descriptorMap:
 		if value.IsNil() {
@@ -201,14 +156,14 @@ func collectChangedSecretStates(value reflect.Value, descriptor *typeDescriptor,
 		keys := value.MapKeys()
 		slices.SortFunc(keys, func(left, right reflect.Value) int { return cmp.Compare(left.String(), right.String()) })
 		for _, key := range keys {
-			collectChangedSecretStates(value.MapIndex(key), descriptor.element, path.Key(key.String()), lookups, changed)
+			collectChangedSecretStates(value.MapIndex(key), descriptor.element, secrets, path.Key(key.String()), lookups, changed)
 		}
 	case descriptorSlice, descriptorArray:
 		if descriptor.kind == descriptorSlice && value.IsNil() {
 			return
 		}
 		for index := 0; index < value.Len(); index++ {
-			collectChangedSecretStates(value.Index(index), descriptor.element, path.Index(index), lookups, changed)
+			collectChangedSecretStates(value.Index(index), descriptor.element, secrets, path.Index(index), lookups, changed)
 		}
 	}
 }

internal/engine/secret_reference_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"encoding/json"
@@ -18,6 +18,16 @@ type secretReferenceConfig struct {
 	Sequence []Secret           `yaml:"sequence"`
 }
 
+type resolutionQueryReader struct {
+	input *strings.Reader
+	reads int
+}
+
+func (reader *resolutionQueryReader) Read(data []byte) (int, error) {
+	reader.reads++
+	return reader.input.Read(data)
+}
+
 func TestSecretReferencesResolveTypedShapesOncePerName(t *testing.T) {
 	input := `required: SHARED_SECRET
 optional: OPTIONAL_SECRET
@@ -41,7 +51,7 @@ sequence: [SHARED_SECRET, SEQUENCE_SECRET]
 		return value, present
 	}
 	validationCalled := false
-	result, err := loadWithSecretLookup(Bytes("secrets.yml", []byte(input)), lookup, Options[secretReferenceConfig]{
+	result, err := testLoadWithSecretLookup(Bytes("secrets.yml", []byte(input)), lookup, Options[secretReferenceConfig]{
 		Definition: Definition[secretReferenceConfig]{Validate: func(configuration *secretReferenceConfig, validation *Validation) {
 			validationCalled = true
 			if configuration.Required.Value() != "shared-value" || !configuration.Required.IsResolved() ||
@@ -52,7 +62,7 @@ sequence: [SHARED_SECRET, SEQUENCE_SECRET]
 		}},
 	})
 	if err != nil {
-		t.Fatalf("loadWithSecretLookup() error = %v", err)
+		t.Fatalf("testLoadWithSecretLookup() error = %v", err)
 	}
 	if !validationCalled || result.Config.Optional == nil || result.Config.Pointers["nil"] != nil {
 		t.Fatalf("resolved config = %#v", result.Config)
@@ -84,7 +94,7 @@ func TestSecretReferenceErrorsAreSafeAndPathSpecific(t *testing.T) {
 			if lookup == nil {
 				lookup = func(string) (string, bool) { return "", false }
 			}
-			_, err := loadWithSecretLookup(Bytes("secret-errors.yml", []byte(test.input)), lookup, Options[secretReferenceConfig]{})
+			_, err := testLoadWithSecretLookup(Bytes("secret-errors.yml", []byte(test.input)), lookup, Options[secretReferenceConfig]{})
 			loadError := requireSecretLoadCode(t, err, test.code)
 			diagnostic := loadError.Diagnostics()[0]
 			if diagnostic.Path.String() != "/required" || strings.Contains(fmt.Sprintf("%v %#v", err, err), "CREDENTIAL-CANARY") {
@@ -97,9 +107,9 @@ func TestSecretReferenceErrorsAreSafeAndPathSpecific(t *testing.T) {
 		type config struct {
 			Optional *Secret `yaml:"optional"`
 		}
-		_, err := loadWithSecretLookup(Bytes("optional.yml", []byte("optional: ''\n")), func(string) (string, bool) { return "", false }, Options[config]{})
+		_, err := testLoadWithSecretLookup(Bytes("optional.yml", []byte("optional: ''\n")), func(string) (string, bool) { return "", false }, Options[config]{})
 		requireSecretLoadCode(t, err, CodeSecretInvalidName)
-		result, err := loadWithSecretLookup(Bytes("optional.yml", []byte("optional: null\n")), func(string) (string, bool) { return "", false }, Options[config]{})
+		result, err := testLoadWithSecretLookup(Bytes("optional.yml", []byte("optional: null\n")), func(string) (string, bool) { return "", false }, Options[config]{})
 		if err != nil || result.Config.Optional != nil {
 			t.Fatalf("nil optional result = %#v, %v", result, err)
 		}
@@ -110,7 +120,7 @@ func TestSecretReferenceErrorsAreSafeAndPathSpecific(t *testing.T) {
 			Secrets []Secret `yaml:"secrets"`
 		}
 		lookups := 0
-		_, err := loadWithSecretLookup(Bytes("missing-twice.yml", []byte("secrets: [MISSING_SHARED, MISSING_SHARED]\n")), func(string) (string, bool) {
+		_, err := testLoadWithSecretLookup(Bytes("missing-twice.yml", []byte("secrets: [MISSING_SHARED, MISSING_SHARED]\n")), func(string) (string, bool) {
 			lookups++
 			return "", false
 		}, Options[config]{})
@@ -128,7 +138,7 @@ func TestResolutionSelectsEffectiveSecretNameBeforeLookup(t *testing.T) {
 	}
 	lookedUp := []string{}
 	validated := ""
-	result, err := loadWithSecretLookup(Bytes("resolved-secret.yml", []byte("name: SELECTED_SECRET\nsecret: OLD_SECRET\n")), func(name string) (string, bool) {
+	result, err := testLoadWithSecretLookup(Bytes("resolved-secret.yml", []byte("name: SELECTED_SECRET\nsecret: OLD_SECRET\n")), func(name string) (string, bool) {
 		lookedUp = append(lookedUp, name)
 		return "resolved-value", true
 	}, Options[config]{Definition: Definition[config]{
@@ -141,7 +151,7 @@ func TestResolutionSelectsEffectiveSecretNameBeforeLookup(t *testing.T) {
 		},
 	}})
 	if err != nil {
-		t.Fatalf("loadWithSecretLookup() error = %v", err)
+		t.Fatalf("testLoadWithSecretLookup() error = %v", err)
 	}
 	if !reflect.DeepEqual(lookedUp, []string{"SELECTED_SECRET"}) || validated != "resolved-value" || result.Config.Secret.EnvName() != "SELECTED_SECRET" {
 		t.Fatalf("lookups = %#v, validated = %q, config = %#v", lookedUp, validated, result.Config)
@@ -152,11 +162,55 @@ func TestResolutionSelectsEffectiveSecretNameBeforeLookup(t *testing.T) {
 	}
 }
 
+func TestResolutionInputQueriesDoNotReadOrResolveSecrets(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Value  string `yaml:"value"`
+		Secret Secret `yaml:"secret"`
+	}
+	reader := &resolutionQueryReader{input: strings.NewReader("value: source\nsecret: QUERY_SECRET\n")}
+	lookups := 0
+	var callbackErr error
+	result, err := testLoadWithSecretLookup(Reader("query.yml", reader), func(name string) (string, bool) {
+		lookups++
+		if name != "QUERY_SECRET" {
+			t.Fatalf("secret lookup name = %q", name)
+		}
+		return "query-credential", true
+	}, Options[config]{Definition: Definition[config]{Resolve: func(_ *config, resolution *Resolution) error {
+		reads := reader.reads
+		value, valueFound := resolution.InputInfo(Keys("value"))
+		secret, secretFound := resolution.InputInfo(Keys("secret"))
+		if !valueFound || !secretFound || len(value.Origin.Locations) != 1 || len(secret.Origin.Locations) != 1 {
+			callbackErr = errors.New("entry metadata is incomplete")
+			return callbackErr
+		}
+		if source, found := resolution.Source(value.Origin.Locations[0].SourceID); !found || source.Path != "" {
+			callbackErr = errors.New("entry source is incomplete")
+			return callbackErr
+		}
+		if reader.reads != reads || lookups != 0 {
+			callbackErr = errors.New("entry query performed input or credential access")
+		}
+		return callbackErr
+	}}})
+	if callbackErr != nil {
+		t.Fatal(callbackErr)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	if lookups != 1 || result.Config.Secret.Value() != "query-credential" {
+		t.Fatalf("secret resolution = lookups %d config %#v", lookups, result.Config)
+	}
+}
+
 func TestValidationCannotReplaceResolvedSecretWithSameName(t *testing.T) {
 	type config struct {
 		Secret Secret `yaml:"secret"`
 	}
-	_, err := loadWithSecretLookup(Bytes("validator.yml", []byte("secret: VALIDATOR_SECRET\n")), func(string) (string, bool) {
+	_, err := testLoadWithSecretLookup(Bytes("validator.yml", []byte("secret: VALIDATOR_SECRET\n")), func(string) (string, bool) {
 		return "CREDENTIAL-CANARY", true
 	}, Options[config]{Definition: Definition[config]{Validate: func(configuration *config, validation *Validation) {
 		configuration.Secret = SecretEnv(configuration.Secret.EnvName())
@@ -171,13 +225,13 @@ func TestResolvedDefaultsAreRebuiltAndLaterLoadsRelookup(t *testing.T) {
 	type config struct {
 		Secret Secret `yaml:"secret"`
 	}
-	first, err := loadWithSecretLookup(NoSource(), func(string) (string, bool) { return "first-value", true }, Options[config]{
+	first, err := testLoadWithSecretLookup(NoSource(), func(string) (string, bool) { return "first-value", true }, Options[config]{
 		Definition: Definition[config]{Defaults: func() config { return config{Secret: SecretEnv("DEFAULT_SECRET")} }},
 	})
 	if err != nil {
 		t.Fatal(err)
 	}
-	second, err := loadWithSecretLookup(NoSource(), func(string) (string, bool) { return "second-value", true }, Options[config]{
+	second, err := testLoadWithSecretLookup(NoSource(), func(string) (string, bool) { return "second-value", true }, Options[config]{
 		Definition: Definition[config]{Defaults: func() config { return first.Config }},
 	})
 	if err != nil {
@@ -189,14 +243,14 @@ func TestResolvedDefaultsAreRebuiltAndLaterLoadsRelookup(t *testing.T) {
 
 	t.Setenv("CONFIGKIT_RELOOKUP_SECRET", "one")
 	options := Options[config]{Definition: Definition[config]{Defaults: func() config { return config{Secret: SecretEnv("CONFIGKIT_RELOOKUP_SECRET")} }}}
-	realFirst, err := Load(NoSource(), options)
+	realFirst, err := testLoad(NoSource(), options)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if err := os.Setenv("CONFIGKIT_RELOOKUP_SECRET", "two"); err != nil {
 		t.Fatal(err)
 	}
-	realSecond, err := Load(NoSource(), options)
+	realSecond, err := testLoad(NoSource(), options)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -222,7 +276,7 @@ func TestSecretSafeFormattingJSONProjectionAndHistory(t *testing.T) {
 	type config struct {
 		Secret Secret `yaml:"secret"`
 	}
-	result, err := loadWithSecretLookup(Bytes("safe-secret.yml", []byte("secret: SAFE_SECRET_NAME\n")), func(string) (string, bool) {
+	result, err := testLoadWithSecretLookup(Bytes("safe-secret.yml", []byte("secret: SAFE_SECRET_NAME\n")), func(string) (string, bool) {
 		return credential, true
 	}, Options[config]{})
 	if err != nil {
@@ -263,7 +317,7 @@ func TestBootstrapExistingEmptyWinsAndReferenceFails(t *testing.T) {
 	type config struct {
 		Secret Secret `yaml:"secret"`
 	}
-	_, err = Load[config](Bytes("blocked.yml", []byte("secret: "+name+"\n")))
+	_, err = testLoad[config](Bytes("blocked.yml", []byte("secret: "+name+"\n")))
 	requireSecretLoadCode(t, err, CodeSecretEmpty)
 	if value, present := os.LookupEnv(name); !present || value != "" {
 		t.Fatalf("environment changed to %q, %v", value, present)
@@ -285,7 +339,7 @@ func TestDynamicValuesDoNotEstablishSecretReferences(t *testing.T) {
 		}
 	}
 	lookups := 0
-	result, err := loadWithSecretLookup(Bytes("dynamic.yml", []byte("dynamic: ORDINARY_STRING\n")), func(string) (string, bool) {
+	result, err := testLoadWithSecretLookup(Bytes("dynamic.yml", []byte("dynamic: ORDINARY_STRING\n")), func(string) (string, bool) {
 		lookups++
 		return "unexpected", true
 	}, Options[config]{})
@@ -300,9 +354,9 @@ func TestLoadDoesNotMutateSecretEnvironment(t *testing.T) {
 	type config struct {
 		Secret Secret `yaml:"secret"`
 	}
-	result, err := Load[config](Bytes("unchanged.yml", []byte("secret: "+name+"\n")))
+	result, err := testLoad[config](Bytes("unchanged.yml", []byte("secret: "+name+"\n")))
 	if err != nil || result.Config.Secret.Value() != "original" {
-		t.Fatalf("Load() = %#v, %v", result, err)
+		t.Fatalf("testLoad() = %#v, %v", result, err)
 	}
 	if got := os.Getenv(name); got != "original" {
 		t.Fatalf("environment = %q", got)

internal/engine/secrets.go

@@ -0,0 +1,376 @@
+package engine
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+const (
+	secretsEntryLimit   = 1024
+	secretFileByteLimit = int64(1 << 20)
+	secretsByteLimit    = int64(8 << 20)
+)
+
+// SecretFileStatus describes the outcome for one file considered by
+// LoadSecretsDir.
+type SecretFileStatus string
+
+const (
+	SecretFileLoaded          SecretFileStatus = "loaded"
+	SecretFileSkippedExisting SecretFileStatus = "skipped_existing"
+	SecretFileNotApplied      SecretFileStatus = "not_applied"
+	SecretFileFailed          SecretFileStatus = "failed"
+)
+
+// SecretFileResult is the safe, value-free bootstrap result for one directory
+// entry. ExistingEmpty is meaningful when Status is SecretFileSkippedExisting.
+type SecretFileResult struct {
+	Name          string
+	Path          string
+	Status        SecretFileStatus
+	ExistingEmpty bool
+}
+
+// SecretsReport is a detached snapshot of an explicit secrets-directory
+// bootstrap. It does not retain file contents or environment values.
+type SecretsReport struct {
+	entries []SecretFileResult
+}
+
+// Entries returns a copy of the report's filename-ordered entries.
+func (r *SecretsReport) Entries() []SecretFileResult {
+	if r == nil {
+		return nil
+	}
+	return slices.Clone(r.entries)
+}
+
+// WriteTo renders one safe, deterministic line per entry. Names and paths are
+// quoted so control characters cannot affect terminal output.
+func (r *SecretsReport) WriteTo(output io.Writer) (int64, error) {
+	if output == nil {
+		return 0, errors.New("configkit: secrets report output is nil")
+	}
+	if r == nil {
+		return 0, nil
+	}
+	var total int64
+	for _, entry := range r.entries {
+		line := "status=" + strconv.Quote(string(entry.Status)) +
+			" name=" + strconv.Quote(entry.Name) +
+			" path=" + strconv.Quote(entry.Path) +
+			" existing_empty=" + strconv.FormatBool(entry.ExistingEmpty) + "\n"
+		written, err := io.WriteString(output, line)
+		total += int64(written)
+		if err != nil {
+			return total, err
+		}
+		if written != len(line) {
+			return total, io.ErrShortWrite
+		}
+	}
+	return total, nil
+}
+
+// SecretsError reports safe structured diagnostics for a failed explicit
+// secrets-directory bootstrap. It intentionally does not unwrap filesystem or
+// environment errors.
+type SecretsError struct {
+	diagnostics []Diagnostic
+}
+
+// Error implements error without rendering filenames, paths, or file contents.
+func (e *SecretsError) Error() string {
+	if e == nil {
+		return "configkit: secrets bootstrap failed"
+	}
+	count := 0
+	for _, diagnostic := range e.diagnostics {
+		if diagnostic.Severity == SeverityError {
+			count++
+		}
+	}
+	if count == 1 {
+		return "configkit: secrets bootstrap failed with 1 error"
+	}
+	return fmt.Sprintf("configkit: secrets bootstrap failed with %d errors", count)
+}
+
+// Diagnostics returns a deep copy of the bootstrap diagnostics.
+func (e *SecretsError) Diagnostics() []Diagnostic {
+	if e == nil {
+		return nil
+	}
+	return cloneDiagnostics(e.diagnostics)
+}
+
+type secretsEnvironment struct {
+	lookup func(string) (string, bool)
+	set    func(string, string) error
+}
+
+type secretsAccess struct {
+	openDirectory func(string) (*os.File, error)
+	lstat         func(string) (fs.FileInfo, error)
+	openFile      func(string) (*os.File, error)
+}
+
+type stagedSecret struct {
+	entry int
+	value string
+}
+
+// LoadSecretsDir explicitly loads immediate regular files from directory into
+// previously unset process environment variables. Applications should call it
+// once during startup, before concurrent work; Load never calls it.
+// Dot-prefixed entries are ignored and omitted from the report.
+func LoadSecretsDir(directory string) (*SecretsReport, error) {
+	return loadSecretsDir(directory, secretsEnvironment{lookup: os.LookupEnv, set: os.Setenv}, secretsAccess{
+		openDirectory: os.Open,
+		lstat:         os.Lstat,
+		openFile:      os.Open,
+	})
+}
+
+func loadSecretsDir(directory string, environment secretsEnvironment, access secretsAccess) (*SecretsReport, error) {
+	report := &SecretsReport{}
+	if strings.TrimSpace(directory) == "" {
+		return report, secretsFailure(CodeSecretsInvalidPath, "secrets directory path is required")
+	}
+
+	canonical, err := canonicalExistingPath(directory)
+	if err != nil {
+		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be canonicalized: "+strconv.Quote(cleanAbsolutePath(directory)))
+	}
+	info, err := os.Stat(canonical)
+	if err != nil {
+		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be inspected: "+strconv.Quote(canonical))
+	}
+	if !info.IsDir() {
+		return report, secretsFailure(CodeSecretsInvalidPath, "secrets directory is not a directory: "+strconv.Quote(canonical))
+	}
+
+	directoryFile, err := access.openDirectory(canonical)
+	if err != nil {
+		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be opened: "+strconv.Quote(canonical))
+	}
+	entries, readErr := readSecretsEntries(directoryFile)
+	closeErr := directoryFile.Close()
+	if readErr != nil {
+		return report, secretsFailure(classifySecretsFilesystemError(readErr), "secrets directory could not be enumerated: "+strconv.Quote(canonical))
+	}
+	if closeErr != nil {
+		return report, secretsFailure(CodeSecretsRead, "secrets directory could not be closed: "+strconv.Quote(canonical))
+	}
+	entryLimitExceeded := len(entries) > secretsEntryLimit
+	entries = slices.DeleteFunc(entries, func(entry fs.DirEntry) bool {
+		return strings.HasPrefix(entry.Name(), ".")
+	})
+	slices.SortFunc(entries, func(left, right fs.DirEntry) int { return strings.Compare(left.Name(), right.Name()) })
+	report.entries = make([]SecretFileResult, len(entries))
+	for index, entry := range entries {
+		name := entry.Name()
+		report.entries[index] = SecretFileResult{Name: name, Path: filepath.Join(canonical, name), Status: SecretFileNotApplied}
+	}
+	if entryLimitExceeded {
+		return report, secretsFailure(CodeSecretsLimitExceeded, "secrets directory exceeds the 1024-entry limit: "+strconv.Quote(canonical))
+	}
+
+	for index := range report.entries {
+		entry := &report.entries[index]
+		if !validEnvironmentName(entry.Name) {
+			entry.Status = SecretFileFailed
+			return report, secretsFailure(CodeSecretsInvalidName, "secret filename is not a valid environment name: "+strconv.Quote(entry.Path))
+		}
+		info, err := access.lstat(entry.Path)
+		if err != nil {
+			entry.Status = SecretFileFailed
+			return report, secretsFailure(classifySecretsFilesystemError(err), "secret file could not be inspected: "+strconv.Quote(entry.Path))
+		}
+		if info.Mode()&fs.ModeSymlink != 0 || !info.Mode().IsRegular() {
+			entry.Status = SecretFileFailed
+			return report, secretsFailure(CodeSecretsNotRegular, "secret entry is not a regular file: "+strconv.Quote(entry.Path))
+		}
+	}
+
+	staged := make([]stagedSecret, 0, len(report.entries))
+	var consumed int64
+	for index := range report.entries {
+		entry := &report.entries[index]
+		if existing, present := environment.lookup(entry.Name); present {
+			entry.Status = SecretFileSkippedExisting
+			entry.ExistingEmpty = existing == ""
+			continue
+		}
+		remaining := secretsByteLimit - consumed
+		value, used, err := readSecretValue(entry.Path, remaining, access)
+		if err != nil {
+			entry.Status = SecretFileFailed
+			return report, secretsFailure(secretReadCode(err), secretReadMessage(err)+": "+strconv.Quote(entry.Path))
+		}
+		consumed += used
+		staged = append(staged, stagedSecret{entry: index, value: value})
+	}
+
+	for _, secret := range staged {
+		entry := &report.entries[secret.entry]
+		if existing, present := environment.lookup(entry.Name); present {
+			entry.Status = SecretFileSkippedExisting
+			entry.ExistingEmpty = existing == ""
+			continue
+		}
+		if err := environment.set(entry.Name, secret.value); err != nil {
+			entry.Status = SecretFileFailed
+			return report, secretsFailure(CodeSecretsApplyFailed, "secret environment variable could not be set for file: "+strconv.Quote(entry.Path))
+		}
+		entry.Status = SecretFileLoaded
+	}
+	return report, nil
+}
+
+func readSecretsEntries(directory *os.File) ([]fs.DirEntry, error) {
+	entries := make([]fs.DirEntry, 0)
+	for len(entries) <= secretsEntryLimit {
+		batch, err := directory.ReadDir(secretsEntryLimit + 1 - len(entries))
+		entries = append(entries, batch...)
+		if err == io.EOF {
+			return entries, nil
+		}
+		if err != nil {
+			return entries, err
+		}
+		if len(entries) > secretsEntryLimit {
+			return entries, nil
+		}
+	}
+	return entries, nil
+}
+
+type secretReadFailure int
+
+const (
+	secretReadFilesystem secretReadFailure = iota
+	secretReadFileLimit
+	secretReadTotalLimit
+	secretReadNUL
+)
+
+type secretReadError struct {
+	kind secretReadFailure
+	err  error
+}
+
+func (e *secretReadError) Error() string { return "secret read failed" }
+
+func readSecretValue(path string, remaining int64, access secretsAccess) (string, int64, error) {
+	if remaining < 0 {
+		return "", 0, &secretReadError{kind: secretReadTotalLimit}
+	}
+	limit := min(secretFileByteLimit, remaining)
+	file, err := access.openFile(path)
+	if err != nil {
+		return "", 0, &secretReadError{kind: secretReadFilesystem, err: err}
+	}
+	data, readErr := io.ReadAll(io.LimitReader(file, limit+1))
+	closeErr := file.Close()
+	if readErr != nil {
+		return "", 0, &secretReadError{kind: secretReadFilesystem, err: readErr}
+	}
+	if closeErr != nil {
+		return "", 0, &secretReadError{kind: secretReadFilesystem, err: closeErr}
+	}
+	if int64(len(data)) > limit {
+		kind := secretReadFileLimit
+		if remaining < secretFileByteLimit {
+			kind = secretReadTotalLimit
+		}
+		return "", 0, &secretReadError{kind: kind}
+	}
+	if slices.Contains(data, byte(0)) {
+		return "", 0, &secretReadError{kind: secretReadNUL}
+	}
+	value := string(data)
+	if strings.HasSuffix(value, "\r\n") {
+		value = strings.TrimSuffix(value, "\r\n")
+	} else {
+		value = strings.TrimSuffix(value, "\n")
+	}
+	return value, int64(len(data)), nil
+}
+
+func validEnvironmentName(name string) bool {
+	if name == "" || !asciiEnvironmentFirst(name[0]) {
+		return false
+	}
+	for index := 1; index < len(name); index++ {
+		character := name[index]
+		if !asciiEnvironmentFirst(character) && (character < '0' || character > '9') {
+			return false
+		}
+	}
+	return true
+}
+
+func asciiEnvironmentFirst(character byte) bool {
+	return character == '_' || character >= 'A' && character <= 'Z' || character >= 'a' && character <= 'z'
+}
+
+func cleanAbsolutePath(path string) string {
+	absolute, err := filepath.Abs(path)
+	if err != nil {
+		return filepath.Clean(path)
+	}
+	return filepath.Clean(absolute)
+}
+
+func classifySecretsFilesystemError(err error) Code {
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		return CodeSecretsMissing
+	case errors.Is(err, fs.ErrPermission):
+		return CodeSecretsPermission
+	default:
+		return CodeSecretsRead
+	}
+}
+
+func secretReadCode(err error) Code {
+	var failure *secretReadError
+	if errors.As(err, &failure) {
+		switch failure.kind {
+		case secretReadFileLimit, secretReadTotalLimit:
+			return CodeSecretsLimitExceeded
+		case secretReadNUL:
+			return CodeSecretsInvalidValue
+		case secretReadFilesystem:
+			return classifySecretsFilesystemError(failure.err)
+		}
+	}
+	return CodeSecretsRead
+}
+
+func secretReadMessage(err error) string {
+	var failure *secretReadError
+	if errors.As(err, &failure) {
+		switch failure.kind {
+		case secretReadFileLimit:
+			return "secret file exceeds the 1 MiB limit"
+		case secretReadTotalLimit:
+			return "eligible secret files exceed the 8 MiB total limit"
+		case secretReadNUL:
+			return "secret file contains a NUL byte"
+		}
+	}
+	return "secret file could not be read"
+}
+
+func secretsFailure(code Code, message string) *SecretsError {
+	return &SecretsError{diagnostics: []Diagnostic{{Code: code, Severity: SeverityError, Message: message}}}
+}

internal/engine/secrets_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"encoding/json"
@@ -64,6 +64,41 @@ func TestLoadSecretsDirLoadsCanonicalSortedValues(t *testing.T) {
 	}
 }
 
+func TestLoadSecretsDirIgnoresDotEntries(t *testing.T) {
+	directory := t.TempDir()
+	if err := os.Mkdir(filepath.Join(directory, ".git"), 0o700); err != nil {
+		t.Fatal(err)
+	}
+	writeSecretTestFile(t, directory, ".gitignore", "CANARY\x00")
+	writeSecretTestFile(t, directory, ".DS_Store", "CANARY\x00")
+	if runtime.GOOS != "windows" {
+		if err := os.Symlink(filepath.Join(directory, "missing"), filepath.Join(directory, ".hidden-link")); err != nil {
+			t.Fatal(err)
+		}
+	}
+	access := testSecretsAccess()
+	access.lstat = func(path string) (fs.FileInfo, error) {
+		if strings.HasPrefix(filepath.Base(path), ".") {
+			t.Fatalf("inspected ignored entry %q", path)
+		}
+		return os.Lstat(path)
+	}
+	environment := map[string]string{}
+	report, err := loadSecretsDir(directory, mapSecretsEnvironment(environment), access)
+	if err != nil || len(report.Entries()) != 0 || len(environment) != 0 {
+		t.Fatalf("hidden-only directory: error = %v, report = %#v, environment = %#v", err, report.Entries(), environment)
+	}
+	writeSecretTestFile(t, directory, "SECRET", "value\n")
+	report, err = loadSecretsDir(directory, mapSecretsEnvironment(environment), access)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []SecretFileResult{{Name: "SECRET", Path: filepath.Join(canonicalTestPath(t, directory), "SECRET"), Status: SecretFileLoaded}}
+	if !reflect.DeepEqual(report.Entries(), want) || !reflect.DeepEqual(environment, map[string]string{"SECRET": "value"}) {
+		t.Fatalf("mixed directory: report = %#v, environment = %#v", report.Entries(), environment)
+	}
+}
+
 func TestLoadSecretsDirPreservesExistingWithoutReading(t *testing.T) {
 	directory := t.TempDir()
 	writeSecretTestFile(t, directory, "EMPTY_WINNER", strings.Repeat("CANARY", int(secretFileByteLimit)))

internal/engine/selected_overlay.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"
@@ -12,12 +12,12 @@ import (
 	yamladapter "gitea.maximumdirect.net/eric/ConfigKit/internal/yaml"
 )
 
-func activeProfile(name string) bool {
+func activeOverlay(name string) bool {
 	return name != "" && name != "default"
 }
 
-func validProfileName(name string) bool {
-	if !activeProfile(name) {
+func validOverlayName(name string) bool {
+	if !activeOverlay(name) {
 		return true
 	}
 	for _, character := range name {
@@ -31,38 +31,38 @@ func validProfileName(name string) bool {
 	return true
 }
 
-func loadProfileDocument(source Source, context *FilesystemContext, main parsedSource, base *composedDocument, sources []SourceInfo, name string, rule *VersionRule, limits importLimits) (*composedDocument, []SourceInfo, []Diagnostic) {
+func loadSelectedOverlayDocument(source Source, context *FilesystemContext, main parsedSource, base *composedDocument, sources []SourceInfo, name string, rule *VersionRule, limits importLimits) (*composedDocument, []SourceInfo, []Diagnostic) {
 	rootPath, _, _, diagnostic := importFilesystem(source, context, main)
 	if diagnostic != nil {
 		return nil, cloneSourceInfos(sources), []Diagnostic{*diagnostic}
 	}
-	profilePath := filepath.Join(rootPath, "profiles", name+".yml")
-	canonical, err := canonicalExistingPath(profilePath)
+	overlayPath := filepath.Join(rootPath, "overlays", name+".yml")
+	canonical, err := canonicalExistingPath(overlayPath)
 	if err != nil {
-		code := CodeProfileInvalid
-		message := "selected profile could not be resolved"
+		code := CodeOverlayInvalid
+		message := "selected overlay could not be resolved"
 		if errors.Is(err, fs.ErrNotExist) {
-			code, message = CodeProfileMissing, "selected profile does not exist"
+			code, message = CodeOverlayMissing, "selected overlay does not exist"
 		} else if errors.Is(err, fs.ErrPermission) {
-			code, message = CodeImportPermission, "selected profile cannot be accessed"
+			code, message = CodeImportPermission, "selected overlay cannot be accessed"
 		}
 		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(code, message, nil)}
 	}
 	if !containedPath(rootPath, canonical) {
-		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeProfileOutsideRoot, "selected profile resolves outside the configuration root", nil)}
+		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayOutsideRoot, "selected overlay resolves outside the configuration root", nil)}
 	}
 	for _, existing := range sources {
 		if existing.Path != "" && existing.Path == canonical {
-			return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeProfileRepeated, "selected profile is already present in the base source graph", nil)}
+			return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayRepeated, "selected overlay is already present in the base source graph", nil)}
 		}
 	}
 	if len(sources)+1 > limits.sources {
-		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeProfileLimitExceeded, "selected profile exceeds the source-count limit", nil)}
+		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayLimitExceeded, "selected overlay exceeds the source-count limit", nil)}
 	}
 
 	root, err := os.OpenRoot(rootPath)
 	if err != nil {
-		value := globFilesystemDiagnostic(err, "configuration root could not be opened for the selected profile", Location{})
+		value := globFilesystemDiagnostic(err, "configuration root could not be opened for the selected overlay", Location{})
 		value.Primary = nil
 		return nil, cloneSourceInfos(sources), []Diagnostic{value}
 	}
@@ -74,57 +74,57 @@ func loadProfileDocument(source Source, context *FilesystemContext, main parsedS
 	}()
 	relative, err := filepath.Rel(rootPath, canonical)
 	if err != nil || filepath.IsAbs(relative) || relative == ".." || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
-		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeProfileOutsideRoot, "selected profile could not be addressed inside the configuration root", nil)}
+		return nil, cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayOutsideRoot, "selected overlay could not be addressed inside the configuration root", nil)}
 	}
 
 	sourceID := "source-" + strconv.Itoa(len(sources)+1)
-	profileLocation := &Location{SourceID: sourceID}
-	profileSource := SourceInfo{ID: sourceID, Label: filepath.ToSlash(filepath.Join("profiles", name+".yml")), Path: canonical, Layer: LayerProfile}
-	sources = append(cloneSourceInfos(sources), profileSource)
-	data, diagnostic := readProfileFile(root, relative, sourceID, limits.bytes-base.inputBytes)
+	overlayLocation := &Location{SourceID: sourceID}
+	overlaySource := SourceInfo{ID: sourceID, Label: filepath.ToSlash(filepath.Join("overlays", name+".yml")), Path: canonical, Layer: LayerOverlay}
+	sources = append(cloneSourceInfos(sources), overlaySource)
+	data, diagnostic := readOverlayFile(root, relative, sourceID, limits.bytes-base.inputBytes)
 	if diagnostic != nil {
 		return nil, sources, []Diagnostic{*diagnostic}
 	}
-	profileRoot, issues := yamladapter.Parse(bytes.NewReader(data), sourceID, yamladapter.Limits{Depth: maxDocumentDepth, Nodes: maxDocumentNodes})
+	overlayRoot, issues := yamladapter.Parse(bytes.NewReader(data), sourceID, yamladapter.Limits{Depth: maxDocumentDepth, Nodes: maxDocumentNodes})
 	if len(issues) != 0 {
 		return nil, sources, parserDiagnostics(sourceID, issues)
 	}
-	nodeCount := countInputNodes(profileRoot)
+	nodeCount := countInputNodes(overlayRoot)
 	if base.inputNodes+nodeCount > limits.nodes {
-		return nil, sources, []Diagnostic{importDiagnostic(CodeProfileLimitExceeded, "selected profile exceeds the aggregate node limit", profileLocation)}
+		return nil, sources, []Diagnostic{importDiagnostic(CodeOverlayLimitExceeded, "selected overlay exceeds the aggregate node limit", overlayLocation)}
 	}
-	if diagnostics := profileDirectiveDiagnostics(profileRoot, Path{}); len(diagnostics) != 0 {
+	if diagnostics := overlayDirectiveDiagnostics(overlayRoot, Path{}); len(diagnostics) != 0 {
 		return nil, sources, diagnostics
 	}
-	if versionNode := fragmentVersionClaim(profileRoot, rule); versionNode != nil {
+	if versionNode := fragmentVersionClaim(overlayRoot, rule); versionNode != nil {
 		location := publicLocation(versionNode.Location)
 		return nil, sources, []Diagnostic{{
-			Code: CodeProfileVersion, Severity: SeverityError, Path: rule.Path.clone(),
-			Message: "profiles cannot contribute to or replace the schema-version path", Primary: &location,
+			Code: CodeOverlayVersion, Severity: SeverityError, Path: rule.Path.clone(),
+			Message: "overlays cannot contribute to or replace the schema-version path", Primary: &location,
 		}}
 	}
 	closeErr := root.Close()
 	rootClosed = true
 	if closeErr != nil {
-		return nil, sources, []Diagnostic{importDiagnostic(CodeImportRead, "configuration root could not be closed after reading the selected profile", nil)}
+		return nil, sources, []Diagnostic{importDiagnostic(CodeImportRead, "configuration root could not be closed after reading the selected overlay", nil)}
 	}
 
-	profiled, diagnostics := overlayDocuments(base, profileRoot)
-	if profiled != nil {
-		profiled.inputBytes = base.inputBytes + int64(len(data))
-		profiled.inputNodes = base.inputNodes + nodeCount
+	overlayd, diagnostics := overlayDocuments(base, overlayRoot)
+	if overlayd != nil {
+		overlayd.inputBytes = base.inputBytes + int64(len(data))
+		overlayd.inputNodes = base.inputNodes + nodeCount
 	}
-	return profiled, sources, diagnostics
+	return overlayd, sources, diagnostics
 }
 
-func readProfileFile(root *os.Root, relative, sourceID string, remaining int64) ([]byte, *Diagnostic) {
+func readOverlayFile(root *os.Root, relative, sourceID string, remaining int64) ([]byte, *Diagnostic) {
 	limit := min(int64(maxSourceBytes), remaining)
 	if limit < 0 {
 		limit = 0
 	}
 	data, failure := readRegularFile(relative, root.Stat, root.Open, limit)
 	if failure != nil {
-		value := sourceReadDiagnostic(failure, sourceID, CodeProfileLimitExceeded, "selected profile exceeds a source or aggregate byte limit")
+		value := sourceReadDiagnostic(failure, sourceID, CodeOverlayLimitExceeded, "selected overlay exceeds a source or aggregate byte limit")
 		return nil, &value
 	}
 	return data, nil

internal/engine/selected_overlay_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"
@@ -9,7 +9,7 @@ import (
 	"testing"
 )
 
-type profileTestConfig struct {
+type overlayTestConfig struct {
 	Settings struct {
 		Kept    string `yaml:"kept"`
 		Changed string `yaml:"changed"`
@@ -21,7 +21,7 @@ type profileTestConfig struct {
 	Schema   map[string]string `yaml:"schema"`
 }
 
-func TestLoadAppliesSelectedProfileAfterBaseAndBeforeDefaults(t *testing.T) {
+func TestLoadAppliesSelectedOverlayAfterBaseAndBeforeDefaults(t *testing.T) {
 	directory := t.TempDir()
 	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
   imports: [{path: base.yml}]
@@ -33,19 +33,19 @@ nullable: base
 value: {child: base}
 `)
 	basePath := writeImportFile(t, directory, "base.yml", "settings: {added: imported}\n")
-	profilePath := writeImportFile(t, directory, "profiles/testing.yml", `settings:
-  changed: profile
-values: [profile]
+	overlayPath := writeImportFile(t, directory, "overlays/testing.yml", `settings:
+  changed: overlay
+values: [overlay]
 nullable: null
 value: scalar
 `)
 
-	result, err := Load[profileTestConfig](File(mainPath), Options[profileTestConfig]{
+	result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{
 		Imports: true,
-		Profile: "testing",
-		Definition: Definition[profileTestConfig]{Defaults: func() profileTestConfig {
+		Overlay: "testing",
+		Definition: Definition[overlayTestConfig]{Defaults: func() overlayTestConfig {
 			defaultValue := "default"
-			return profileTestConfig{
+			return overlayTestConfig{
 				Values: []string{"default"}, Nullable: &defaultValue,
 				Settings: struct {
 					Kept    string `yaml:"kept"`
@@ -58,31 +58,31 @@ value: scalar
 	if err != nil {
 		t.Fatal(err)
 	}
-	if result.Config.Settings.Kept != "main" || result.Config.Settings.Changed != "profile" || result.Config.Settings.Added != "imported" {
+	if result.Config.Settings.Kept != "main" || result.Config.Settings.Changed != "overlay" || result.Config.Settings.Added != "imported" {
 		t.Fatalf("settings = %#v", result.Config.Settings)
 	}
-	if !reflect.DeepEqual(result.Config.Values, []string{"profile"}) || result.Config.Nullable != nil || result.Config.Value != "scalar" {
-		t.Fatalf("profile values = values %#v nullable %#v value %#v", result.Config.Values, result.Config.Nullable, result.Config.Value)
+	if !reflect.DeepEqual(result.Config.Values, []string{"overlay"}) || result.Config.Nullable != nil || result.Config.Value != "scalar" {
+		t.Fatalf("overlay values = values %#v nullable %#v value %#v", result.Config.Values, result.Config.Nullable, result.Config.Value)
 	}
 	sources := result.Sources()
-	wantPaths := []string{canonicalTestPath(t, mainPath), canonicalTestPath(t, basePath), canonicalTestPath(t, profilePath)}
+	wantPaths := []string{canonicalTestPath(t, mainPath), canonicalTestPath(t, basePath), canonicalTestPath(t, overlayPath)}
 	gotPaths := make([]string, len(sources))
 	for index, source := range sources {
 		gotPaths[index] = source.Path
 	}
-	if !reflect.DeepEqual(gotPaths, wantPaths) || sources[2].Layer != LayerProfile {
+	if !reflect.DeepEqual(gotPaths, wantPaths) || sources[2].Layer != LayerOverlay {
 		t.Fatalf("sources = %#v", sources)
 	}
 	changed, _ := result.Metadata().Lookup(Keys("settings", "changed"))
 	kept, _ := result.Metadata().Lookup(Keys("settings", "kept"))
-	if changed.Origin.Layer != LayerProfile || changed.Origin.Locations[0].SourceID != "source-3" || kept.Origin.Layer != LayerBase {
+	if changed.Origin.Layer != LayerOverlay || changed.Origin.Locations[0].SourceID != "source-3" || kept.Origin.Layer != LayerBase {
 		t.Fatalf("origins = changed %#v kept %#v", changed, kept)
 	}
 	if _, ok := result.Metadata().Lookup(Keys("value", "child")); ok {
 		t.Fatal("removed child remains effective")
 	}
 	childHistory := result.Metadata().History(Keys("value", "child"))
-	if len(childHistory) < 2 || childHistory[len(childHistory)-1].Path.String() != "/value" || childHistory[len(childHistory)-1].Origin.Layer != LayerProfile {
+	if len(childHistory) < 2 || childHistory[len(childHistory)-1].Path.String() != "/value" || childHistory[len(childHistory)-1].Origin.Layer != LayerOverlay {
 		t.Fatalf("removed child history = %#v", childHistory)
 	}
 	if _, ok := result.Metadata().Lookup(Keys("values").Index(1)); ok {
@@ -94,34 +94,43 @@ value: scalar
 	}
 }
 
-func TestLoadProfileSelectionUsesOneFixedYAMLFile(t *testing.T) {
+func TestLoadOverlaySelectionUsesOneFixedYAMLFile(t *testing.T) {
 	directory := t.TempDir()
 	mainPath := writeImportFile(t, directory, "main.yml", "settings: {kept: base}\n")
-	writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: selected}\n")
-	writeImportFile(t, directory, "profiles/default.yml", "settings: {changed: forbidden}\n")
+	writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: selected}\n")
+	writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: legacy}\n")
+	writeImportFile(t, directory, "overlays/default.yml", "settings: {changed: forbidden}\n")
 
 	for _, name := range []string{"", "default"} {
-		result, err := Load[profileTestConfig](File(mainPath), Options[profileTestConfig]{Profile: name})
+		result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: name})
 		if err != nil || result.Config.Settings.Changed != "" || len(result.Sources()) != 1 {
-			t.Fatalf("inactive profile %q = %#v, %v", name, result, err)
+			t.Fatalf("inactive overlay %q = %#v, %v", name, result, err)
 		}
 	}
-	selected, err := Load[profileTestConfig](File(mainPath), Options[profileTestConfig]{Profile: "testing"})
-	if err != nil || selected.Config.Settings.Changed != "selected" || len(selected.Sources()) != 2 {
-		t.Fatalf("selected profile = %#v, %v", selected, err)
+	selected, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: "testing"})
+	if err != nil || selected.Config.Settings.Changed != "selected" || len(selected.Sources()) != 2 ||
+		selected.Sources()[1].Label != "overlays/testing.yml" || selected.Sources()[1].Layer != LayerOverlay {
+		t.Fatalf("selected overlay = %#v, %v", selected, err)
 	}
 
+	t.Run("legacy directory is not selected", func(t *testing.T) {
+		legacyDirectory := t.TempDir()
+		legacyMain := writeImportFile(t, legacyDirectory, "main.yml", "settings: {kept: base}\n")
+		writeImportFile(t, legacyDirectory, "profiles/testing.yml", "settings: {changed: legacy}\n")
+		requireOverlayLoadCode(t, File(legacyMain), Options[overlayTestConfig]{Overlay: "testing"}, CodeOverlayMissing)
+	})
+
 	for _, name := range []string{"../testing", "testing.yml", "one,two", "with space", "é", "bad\x00name"} {
 		t.Run(name, func(t *testing.T) {
-			requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: name}, CodeOptionsInvalid)
+			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: name}, CodeOptionsInvalid)
 		})
 	}
-	requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "missing"}, CodeProfileMissing)
-	writeImportFile(t, directory, "profiles/fallback.yaml", "settings: {changed: fallback}\n")
-	requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "fallback"}, CodeProfileMissing)
+	requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "missing"}, CodeOverlayMissing)
+	writeImportFile(t, directory, "overlays/fallback.yaml", "settings: {changed: fallback}\n")
+	requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "fallback"}, CodeOverlayMissing)
 }
 
-func TestLoadProfileRejectsDirectivesVersionsAndBaseAliases(t *testing.T) {
+func TestLoadOverlayRejectsDirectivesVersionsAndBaseAliases(t *testing.T) {
 	versionRule := &VersionRule{Path: Keys("schema", "version"), Check: func(version Version, _ *Validation) error {
 		if !version.Present || version.Text != "4" {
 			return errors.New("unexpected version")
@@ -130,55 +139,55 @@ func TestLoadProfileRejectsDirectivesVersionsAndBaseAliases(t *testing.T) {
 	}}
 	for _, test := range []struct {
 		name    string
-		profile string
+		overlay string
 		code    Code
 	}{
-		{name: "root directive", profile: "configkit: {}\n", code: CodeProfileDirective},
-		{name: "nested directive", profile: "settings: {configkit: {}}\n", code: CodeProfileDirective},
-		{name: "equal integer version", profile: "schema: {version: 4}\n", code: CodeProfileVersion},
-		{name: "ancestor scalar", profile: "schema: null\n", code: CodeProfileVersion},
+		{name: "root directive", overlay: "configkit: {}\n", code: CodeOverlayDirective},
+		{name: "nested directive", overlay: "settings: {configkit: {}}\n", code: CodeOverlayDirective},
+		{name: "equal integer version", overlay: "schema: {version: 4}\n", code: CodeOverlayVersion},
+		{name: "ancestor scalar", overlay: "schema: null\n", code: CodeOverlayVersion},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			directory := t.TempDir()
 			mainPath := writeImportFile(t, directory, "main.yml", "schema: {version: 4}\n")
-			writeImportFile(t, directory, "profiles/testing.yml", test.profile)
-			requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "testing", Definition: Definition[profileTestConfig]{Version: versionRule}}, test.code)
+			writeImportFile(t, directory, "overlays/testing.yml", test.overlay)
+			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing", Definition: Definition[overlayTestConfig]{Version: versionRule}}, test.code)
 		})
 	}
 
 	t.Run("mapping sibling is allowed", func(t *testing.T) {
 		directory := t.TempDir()
 		mainPath := writeImportFile(t, directory, "main.yml", "schema: {version: 4}\n")
-		writeImportFile(t, directory, "profiles/testing.yml", "schema: {other: allowed}\n")
-		result, err := Load[profileTestConfig](File(mainPath), Options[profileTestConfig]{Profile: "testing", Definition: Definition[profileTestConfig]{Version: versionRule}})
+		writeImportFile(t, directory, "overlays/testing.yml", "schema: {other: allowed}\n")
+		result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: "testing", Definition: Definition[overlayTestConfig]{Version: versionRule}})
 		if err != nil || result.Config.Schema["other"] != "allowed" {
 			t.Fatalf("mapping sibling = %#v, %v", result, err)
 		}
 	})
 
-	t.Run("profile aliases imported base", func(t *testing.T) {
+	t.Run("overlay aliases imported base", func(t *testing.T) {
 		directory := t.TempDir()
-		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: profiles/testing.yml}]}\n")
-		writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: value}\n")
-		requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Imports: true, Profile: "testing"}, CodeProfileRepeated)
+		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: overlays/testing.yml}]}\n")
+		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: value}\n")
+		requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Imports: true, Overlay: "testing"}, CodeOverlayRepeated)
 	})
 }
 
-func TestLoadProfileKeepsBaseFailuresAndFilesystemContainment(t *testing.T) {
-	t.Run("base parse precedes profile", func(t *testing.T) {
+func TestLoadOverlayKeepsBaseFailuresAndFilesystemContainment(t *testing.T) {
+	t.Run("base parse precedes overlay", func(t *testing.T) {
 		directory := t.TempDir()
 		mainPath := writeImportFile(t, directory, "main.yml", "settings: [\n")
-		writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: profile}\n")
-		requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "testing"}, CodeYAMLInvalid)
+		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: overlay}\n")
+		requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeYAMLInvalid)
 	})
 
-	t.Run("profile parse", func(t *testing.T) {
+	t.Run("overlay parse", func(t *testing.T) {
 		directory := t.TempDir()
 		mainPath := writeImportFile(t, directory, "main.yml", "{}\n")
-		writeImportFile(t, directory, "profiles/testing.yml", "settings: [\n")
-		loadError := requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "testing"}, CodeYAMLInvalid)
+		writeImportFile(t, directory, "overlays/testing.yml", "settings: [\n")
+		loadError := requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeYAMLInvalid)
 		if loadError.Diagnostics()[0].Primary.SourceID != "source-2" || len(loadError.Sources()) != 2 {
-			t.Fatalf("profile parse attribution = %#v / %#v", loadError.Diagnostics(), loadError.Sources())
+			t.Fatalf("overlay parse attribution = %#v / %#v", loadError.Diagnostics(), loadError.Sources())
 		}
 	})
 
@@ -186,32 +195,32 @@ func TestLoadProfileKeepsBaseFailuresAndFilesystemContainment(t *testing.T) {
 		t.Run("symlink escape", func(t *testing.T) {
 			root := t.TempDir()
 			outside := t.TempDir()
-			outsideProfile := writeImportFile(t, outside, "testing.yml", "settings: {changed: outside}\n")
-			if err := os.Mkdir(filepath.Join(root, "profiles"), 0o755); err != nil {
+			outsideOverlay := writeImportFile(t, outside, "testing.yml", "settings: {changed: outside}\n")
+			if err := os.Mkdir(filepath.Join(root, "overlays"), 0o755); err != nil {
 				t.Fatal(err)
 			}
-			if err := os.Symlink(outsideProfile, filepath.Join(root, "profiles/testing.yml")); err != nil {
+			if err := os.Symlink(outsideOverlay, filepath.Join(root, "overlays/testing.yml")); err != nil {
 				t.Skipf("symlinks unavailable: %v", err)
 			}
 			mainPath := writeImportFile(t, root, "main.yml", "{}\n")
-			requireProfileLoadCode(t, File(mainPath), Options[profileTestConfig]{Profile: "testing"}, CodeProfileOutsideRoot)
+			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeOverlayOutsideRoot)
 		})
 	}
 
 	t.Run("byte source context", func(t *testing.T) {
 		directory := t.TempDir()
-		writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: selected}\n")
-		result, err := Load[profileTestConfig](Bytes("s3://bucket/main.yml", []byte("{}\n")), Options[profileTestConfig]{
-			Profile: "testing", Filesystem: &FilesystemContext{BaseDir: directory, Root: directory},
+		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: selected}\n")
+		result, err := testLoad[overlayTestConfig](Bytes("s3://bucket/main.yml", []byte("{}\n")), Options[overlayTestConfig]{
+			Overlay: "testing", Filesystem: &FilesystemContext{BaseDir: directory, Root: directory},
 		})
 		if err != nil || result.Config.Settings.Changed != "selected" {
-			t.Fatalf("byte profile = %#v, %v", result, err)
+			t.Fatalf("byte overlay = %#v, %v", result, err)
 		}
-		requireProfileLoadCode(t, Bytes("memory.yml", []byte("{}\n")), Options[profileTestConfig]{Profile: "testing"}, CodeOptionsInvalid)
+		requireOverlayLoadCode(t, Bytes("memory.yml", []byte("{}\n")), Options[overlayTestConfig]{Overlay: "testing"}, CodeOptionsInvalid)
 	})
 }
 
-func TestLoadProfileCountsAgainstAggregateBudgets(t *testing.T) {
+func TestLoadOverlayCountsAgainstAggregateBudgets(t *testing.T) {
 	for _, test := range []struct {
 		name   string
 		limits func(parsedSource, int) importLimits
@@ -219,8 +228,8 @@ func TestLoadProfileCountsAgainstAggregateBudgets(t *testing.T) {
 		{name: "source count", limits: func(_ parsedSource, _ int) importLimits {
 			return importLimits{sources: 1, bytes: maxTotalBytes, nodes: maxDocumentNodes}
 		}},
-		{name: "aggregate bytes", limits: func(main parsedSource, profileBytes int) importLimits {
-			return importLimits{sources: 2, bytes: main.bytes + int64(profileBytes) - 1, nodes: maxDocumentNodes}
+		{name: "aggregate bytes", limits: func(main parsedSource, overlayBytes int) importLimits {
+			return importLimits{sources: 2, bytes: main.bytes + int64(overlayBytes) - 1, nodes: maxDocumentNodes}
 		}},
 		{name: "aggregate nodes", limits: func(main parsedSource, _ int) importLimits {
 			return importLimits{sources: 2, bytes: maxTotalBytes, nodes: countInputNodes(main.document) + 1}
@@ -229,8 +238,8 @@ func TestLoadProfileCountsAgainstAggregateBudgets(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			directory := t.TempDir()
 			mainPath := writeImportFile(t, directory, "main.yml", "{}\n")
-			profileData := "settings: {changed: selected}\n"
-			writeImportFile(t, directory, "profiles/testing.yml", profileData)
+			overlayData := "settings: {changed: selected}\n"
+			writeImportFile(t, directory, "overlays/testing.yml", overlayData)
 			main, diagnostics := parseSource(File(mainPath), "source-1", defaultParseLimits())
 			if len(diagnostics) != 0 {
 				t.Fatal(diagnostics)
@@ -241,17 +250,17 @@ func TestLoadProfileCountsAgainstAggregateBudgets(t *testing.T) {
 			}
 			base.inputBytes = main.bytes
 			base.inputNodes = countInputNodes(main.document)
-			_, _, diagnostics = loadProfileDocument(File(mainPath), nil, main, base, sourceInfos(main.source), "testing", nil, test.limits(main, len(profileData)))
-			if len(diagnostics) == 0 || diagnostics[0].Code != CodeProfileLimitExceeded {
+			_, _, diagnostics = loadSelectedOverlayDocument(File(mainPath), nil, main, base, sourceInfos(main.source), "testing", nil, test.limits(main, len(overlayData)))
+			if len(diagnostics) == 0 || diagnostics[0].Code != CodeOverlayLimitExceeded {
 				t.Fatalf("diagnostics = %#v", diagnostics)
 			}
 		})
 	}
 }
 
-func requireProfileLoadCode(t *testing.T, source Source, options Options[profileTestConfig], code Code) *LoadError {
+func requireOverlayLoadCode(t *testing.T, source Source, options Options[overlayTestConfig], code Code) *LoadError {
 	t.Helper()
-	result, err := Load[profileTestConfig](source, options)
+	result, err := testLoad[overlayTestConfig](source, options)
 	if result != nil || err == nil {
 		t.Fatalf("result, error = %#v, %v", result, err)
 	}

internal/engine/snapshot.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"bytes"

internal/engine/source.go

@@ -0,0 +1,216 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"reflect"
+	"sync/atomic"
+)
+
+const (
+	maxSourceBytes = 8 << 20
+	maxTotalBytes  = 64 << 20
+)
+
+// Source is an opaque configuration input. Construct sources with File, Bytes,
+// Reader, or NoSource; the zero value is invalid.
+type Source struct {
+	kind      sourceKind
+	path      string
+	label     string
+	data      []byte
+	reader    *readerSource
+	createErr sourceCreationError
+}
+
+type sourceKind uint8
+
+const (
+	sourceInvalid sourceKind = iota
+	sourceFile
+	sourceBytes
+	sourceReader
+	sourceNone
+)
+
+type sourceCreationError uint8
+
+const (
+	creationValid sourceCreationError = iota
+	creationInvalidPath
+	creationInvalidLabel
+	creationInvalidReader
+	creationTooLarge
+)
+
+type readerSource struct {
+	input io.Reader
+	used  atomic.Bool
+}
+
+// File returns a source that reopens path for every load attempt.
+func File(path string) Source {
+	if path == "" {
+		return Source{kind: sourceFile, createErr: creationInvalidPath}
+	}
+	return Source{kind: sourceFile, path: path, label: path}
+}
+
+// Bytes snapshots data immediately. Label must be nonempty and safe to display;
+// constructor problems are reported when the source is consumed.
+func Bytes(label string, data []byte) Source {
+	source := Source{kind: sourceBytes, label: label}
+	if label == "" {
+		source.createErr = creationInvalidLabel
+		return source
+	}
+	if len(data) > maxSourceBytes {
+		source.createErr = creationTooLarge
+		return source
+	}
+	source.data = bytes.Clone(data)
+	return source
+}
+
+// Reader returns a single-use source. ConfigKit consumes input but never closes it.
+// Copies of the returned Source share the same single-use claim.
+func Reader(label string, input io.Reader) Source {
+	source := Source{kind: sourceReader, label: label}
+	if label == "" {
+		source.createErr = creationInvalidLabel
+		return source
+	}
+	if nilReader(input) {
+		source.createErr = creationInvalidReader
+		return source
+	}
+	source.reader = &readerSource{input: input}
+	return source
+}
+
+// NoSource explicitly selects a defaults-only input. It creates no source record.
+func NoSource() Source {
+	return Source{kind: sourceNone}
+}
+
+type sourceLimits struct {
+	perSource int64
+	remaining int64
+}
+
+func defaultSourceLimits() sourceLimits {
+	return sourceLimits{perSource: maxSourceBytes, remaining: maxTotalBytes}
+}
+
+type sourceRead struct {
+	data []byte
+	info *SourceInfo
+}
+
+func readSource(source Source, sourceID string, limits sourceLimits) (sourceRead, []Diagnostic) {
+	if diagnostic := sourceConstructorDiagnostic(source); diagnostic != nil {
+		return sourceRead{}, []Diagnostic{*diagnostic}
+	}
+	if source.kind == sourceNone {
+		return sourceRead{}, nil
+	}
+
+	limit := min(limits.perSource, limits.remaining)
+	if limit < 0 {
+		limit = 0
+	}
+	info := &SourceInfo{ID: sourceID, Label: source.label, Layer: LayerBase}
+
+	var input io.Reader
+	switch source.kind {
+	case sourceFile:
+		absolute, err := filepath.Abs(source.path)
+		if err != nil {
+			return sourceRead{info: info}, []Diagnostic{sourceDiagnostic(CodeSourceRead, sourceID, "source path could not be resolved")}
+		}
+		info.Path = filepath.Clean(absolute)
+		canonical, err := filepath.EvalSymlinks(info.Path)
+		if err != nil {
+			return sourceRead{info: info}, []Diagnostic{classifySourceError(err, sourceID)}
+		}
+		info.Path = canonical
+		data, failure := readRegularFile(canonical, os.Stat, os.Open, limit)
+		if failure != nil {
+			return sourceRead{info: info}, []Diagnostic{sourceReadDiagnostic(failure, sourceID, CodeSourceLimitExceeded, "source exceeds the configured byte limit")}
+		}
+		return sourceRead{data: bytes.Clone(data), info: info}, nil
+	case sourceBytes:
+		input = bytes.NewReader(source.data)
+	case sourceReader:
+		if !source.reader.used.CompareAndSwap(false, true) {
+			return sourceRead{info: info}, []Diagnostic{sourceDiagnostic(CodeSourceReaderUsed, sourceID, "reader source has already been consumed")}
+		}
+		input = source.reader.input
+	default:
+		return sourceRead{info: info}, []Diagnostic{sourceDiagnostic(CodeSourceInvalid, sourceID, "source is invalid")}
+	}
+	data, failure := readBoundedSource(input, limit)
+	if failure != nil {
+		return sourceRead{info: info}, []Diagnostic{sourceReadDiagnostic(failure, sourceID, CodeSourceLimitExceeded, "source exceeds the configured byte limit")}
+	}
+	return sourceRead{data: bytes.Clone(data), info: info}, nil
+}
+
+func sourceConstructorDiagnostic(source Source) *Diagnostic {
+	var message string
+	code := CodeSourceInvalid
+	switch source.createErr {
+	case creationValid:
+		if source.kind != sourceInvalid {
+			return nil
+		}
+		message = "source is invalid"
+	case creationInvalidPath:
+		message = "source path must not be empty"
+	case creationInvalidLabel:
+		message = "source label must not be empty"
+	case creationInvalidReader:
+		message = "source reader must not be nil"
+	case creationTooLarge:
+		code = CodeSourceLimitExceeded
+		message = "source exceeds the configured byte limit"
+	}
+	diagnostic := sourceDiagnostic(code, "", message)
+	return &diagnostic
+}
+
+func classifySourceError(err error, sourceID string) Diagnostic {
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		return sourceDiagnostic(CodeSourceMissing, sourceID, "source does not exist")
+	case errors.Is(err, fs.ErrPermission):
+		return sourceDiagnostic(CodeSourcePermission, sourceID, "source cannot be accessed")
+	default:
+		return sourceDiagnostic(CodeSourceRead, sourceID, "source could not be read")
+	}
+}
+
+func sourceDiagnostic(code Code, sourceID, message string) Diagnostic {
+	diagnostic := Diagnostic{Code: code, Severity: SeverityError, Message: message}
+	if sourceID != "" {
+		diagnostic.Primary = &Location{SourceID: sourceID}
+	}
+	return diagnostic
+}
+
+func nilReader(input io.Reader) bool {
+	if input == nil {
+		return true
+	}
+	value := reflect.ValueOf(input)
+	switch value.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
+		return value.IsNil()
+	default:
+		return false
+	}
+}

internal/engine/source_fifo_test.go

@@ -1,6 +1,6 @@
 //go:build darwin || linux
 
-package configkit
+package engine
 
 import (
 	"context"
@@ -23,10 +23,10 @@ func TestNonregularSourcesDoNotBlock(t *testing.T) {
 			source = File(filepath.Join(root, "pipe.yml"))
 		case "import":
 			opts.Imports = true
-		case "profile":
-			opts.Profile = "fifo"
+		case "overlay":
+			opts.Overlay = "fifo"
 		}
-		_, err := Load(source, opts)
+		_, err := testLoad(source, opts)
 		var loadErr *LoadError
 		if !errors.As(err, &loadErr) {
 			t.Fatalf("expected safe load error, got %v", err)
@@ -38,7 +38,7 @@ func TestNonregularSourcesDoNotBlock(t *testing.T) {
 		}
 		t.Fatalf("expected nonregular classification, got %v", loadErr.Diagnostics())
 	}
-	for _, mode := range []string{"file", "import", "profile"} {
+	for _, mode := range []string{"file", "import", "overlay"} {
 		t.Run(mode, func(t *testing.T) {
 			root := t.TempDir()
 			input := "value: 1\n"
@@ -48,12 +48,12 @@ func TestNonregularSourcesDoNotBlock(t *testing.T) {
 			if err := os.WriteFile(filepath.Join(root, "config.yml"), []byte(input), 0600); err != nil {
 				t.Fatal(err)
 			}
-			if err := os.Mkdir(filepath.Join(root, "profiles"), 0700); err != nil {
+			if err := os.Mkdir(filepath.Join(root, "overlays"), 0700); err != nil {
 				t.Fatal(err)
 			}
 			fifo := filepath.Join(root, "pipe.yml")
-			if mode == "profile" {
-				fifo = filepath.Join(root, "profiles", "fifo.yml")
+			if mode == "overlay" {
+				fifo = filepath.Join(root, "overlays", "fifo.yml")
 			}
 			if err := syscall.Mkfifo(fifo, 0600); err != nil {
 				t.Fatal(err)

internal/engine/source_file.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"

internal/engine/source_file_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"io/fs"

internal/engine/source_test.go

@@ -1,4 +1,4 @@
-package configkit
+package engine
 
 import (
 	"errors"