Prepare ConfigKit v0.7.1 release

README.md

@@ -20,7 +20,11 @@ secrets-directory bootstrap is available as a separate startup operation. Explic
 CLI override records apply above overlays. Value explanation is available through
 detached structured records and deterministic redacted output. Built-in
 `extends` relationships let a mapping inherit from a named sibling during the
-same load, retaining explicit presence and source/derivation history.
+same load, retaining explicit presence and source/derivation history. The root
+`Diff` API compares frozen effective values from two successful same-type loads;
+the [configuration contract](docs/config.md#effective-configuration-diffs) and
+[consumer guide](docs/consumers/README.md#effective-configuration-diffs) describe
+its safe changed-region records and maintained workflows.
 
 ```go
 type Config struct {

development_check_test.go

@@ -66,7 +66,7 @@ func TestDevelopmentCheckHandlesFilenamesAndStopsOnFailure(t *testing.T) {
 						t.Fatal(err)
 					}
 					cmd := exec.Command("/bin/bash", filepath.Join(root, "scripts", scriptName))
-					cmd.Env = append(os.Environ(), "PATH="+bin+string(os.PathListSeparator)+os.Getenv("PATH"), "CONFIGKIT_BASELINE_TOOLCHAIN=test-baseline", "CONFIGKIT_NEWER_TOOLCHAIN=", "CONFIGKIT_TEST_FMT_LOG="+log, "CONFIGKIT_TEST_GO_LOG="+calls)
+					cmd.Env = append(os.Environ(), "PATH="+bin+string(os.PathListSeparator)+os.Getenv("PATH"), "CONFIGKIT_TEST_FMT_LOG="+log, "CONFIGKIT_TEST_GO_LOG="+calls)
 					// Log only targets selected by the script, not inherited host settings.
 					cmd.Env = append(cmd.Env, "GOOS=", "GOARCH=")
 					if name == "failed-go-check" {
@@ -108,90 +108,3 @@ func TestDevelopmentCheckHandlesFilenamesAndStopsOnFailure(t *testing.T) {
 		})
 	}
 }
-
-func TestCheckScriptsReleaseGates(t *testing.T) {
-	script, err := os.ReadFile("scripts/release-check.sh")
-	if err != nil {
-		t.Fatal(err)
-	}
-	for _, scenario := range []string{"success", "failed-test", "missing-toolchain"} {
-		t.Run(scenario, func(t *testing.T) {
-			root := t.TempDir()
-			bin := t.TempDir()
-			for _, directory := range []string{"scripts", "nested"} {
-				if err := os.Mkdir(filepath.Join(root, directory), 0700); err != nil {
-					t.Fatal(err)
-				}
-			}
-			checker := filepath.Join(root, "scripts", "release-check.sh")
-			if err := os.WriteFile(checker, script, 0700); err != nil {
-				t.Fatal(err)
-			}
-			calls := filepath.Join(bin, "go.calls")
-			goStub := `#!/bin/sh
-printf '%s|%s|%s|%s|%s|%s\n' "$GOTOOLCHAIN" "$GOPROXY" "${CGO_ENABLED-}" "${GOOS-}" "${GOARCH-}" "$*" >> "$CONFIGKIT_TEST_GO_LOG"
-if [ "${CONFIGKIT_TEST_FAIL-}" = toolchain ] && [ "${1-}" = version ]; then exit 37; fi
-if [ "${CONFIGKIT_TEST_FAIL-}" = test ] && [ "${1-}" = test ]; then exit 37; fi
-`
-			if err := os.WriteFile(filepath.Join(bin, "go"), []byte(goStub), 0700); err != nil {
-				t.Fatal(err)
-			}
-			cmd := exec.Command("/bin/bash", checker)
-			cmd.Dir = filepath.Join(root, "nested")
-			cmd.Env = append(os.Environ(),
-				"PATH="+bin+string(os.PathListSeparator)+os.Getenv("PATH"),
-				"CONFIGKIT_BASELINE_TOOLCHAIN=test-baseline",
-				"CONFIGKIT_TEST_GO_LOG="+calls,
-				"GOOS=", "GOARCH=", "CGO_ENABLED=",
-			)
-			switch scenario {
-			case "failed-test":
-				cmd.Env = append(cmd.Env, "CONFIGKIT_TEST_FAIL=test")
-			case "missing-toolchain":
-				cmd.Env = append(cmd.Env, "CONFIGKIT_TEST_FAIL=toolchain")
-			}
-			output, err := cmd.CombinedOutput()
-			if scenario == "success" && err != nil {
-				t.Fatalf("checker: %v\n%s", err, output)
-			}
-			if scenario != "success" && err == nil {
-				t.Fatalf("checker accepted %s", scenario)
-			}
-			data, err := os.ReadFile(calls)
-			if err != nil {
-				t.Fatal(err)
-			}
-			lines := strings.Split(strings.TrimSpace(string(data)), "\n")
-			for _, line := range lines {
-				if !strings.HasPrefix(line, "test-baseline|off|") {
-					t.Fatalf("toolchain or offline setting lost: %q", line)
-				}
-			}
-			if scenario == "missing-toolchain" {
-				if len(lines) != 1 || !strings.HasSuffix(lines[0], "|version") {
-					t.Fatalf("checker ran after unavailable toolchain: %q", lines)
-				}
-				return
-			}
-			if len(lines) < 2 || lines[1] != "test-baseline|off||||test -mod=readonly -vet=off -race -v ./..." {
-				t.Fatalf("release suite command changed: %q", lines)
-			}
-			if scenario == "failed-test" {
-				if len(lines) != 2 {
-					t.Fatalf("checker continued after failure: %q", lines)
-				}
-				return
-			}
-			want := []string{
-				"test-baseline|off||||version",
-				"test-baseline|off||||test -mod=readonly -vet=off -race -v ./...",
-				"test-baseline|off||||vet -mod=readonly ./...",
-				"test-baseline|off|0|linux|amd64|build -mod=readonly ./...",
-				"test-baseline|off|0|linux|arm64|build -mod=readonly ./...",
-			}
-			if strings.Join(lines, "\n") != strings.Join(want, "\n") {
-				t.Fatalf("unexpected release gates:\n%s", data)
-			}
-		})
-	}
-}

diff.go

@@ -0,0 +1,53 @@
+package configkit
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/engine"
+
+// Difference describes one canonical changed region between two successful
+// loads. Left is the earlier value and Right is the later value. Each snapshot
+// is detached; Present distinguishes absence from an explicit null, and
+// Redacted reports whether combined sensitivity affected that side. Mappings
+// are compared recursively, while sequences are reported as atomic values.
+// Records are ordered by canonical JSON pointer. HiddenChanged indicates that
+// a value concealed by combined sensitivity changed, without revealing which
+// concealed member changed.
+type Difference struct {
+	Path          Path
+	Left          ValueSnapshot
+	Right         ValueSnapshot
+	HiddenChanged bool
+}
+
+// Diff compares the frozen effective values of two successful loads of the
+// same configuration type. It does not reread sources, environment variables,
+// or rerun defaults or resolvers. Equal values produce no records even when
+// their sources, defaults, or resolution histories differ. Credential contents
+// are not compared: typed secret references compare by reference name only.
+//
+// Both results must be non-nil successful loads with inspection state; nil or
+// zero results return an error and no records. Load errors are returned by
+// Load, so callers must handle those before calling Diff. Snapshots are safe
+// for presentation but are not a complete reloadable configuration.
+func Diff[T any](left, right *Result[T]) ([]Difference, error) {
+	var leftInspection, rightInspection *engine.Inspection
+	if left != nil {
+		leftInspection = left.inspection
+	}
+	if right != nil {
+		rightInspection = right.inspection
+	}
+
+	values, err := engine.Diff(leftInspection, rightInspection)
+	if err != nil {
+		return nil, err
+	}
+	differences := make([]Difference, len(values))
+	for index, value := range values {
+		differences[index] = Difference{
+			Path:          fromEnginePath(value.Path),
+			Left:          fromEngineValueSnapshot(value.Left),
+			Right:         fromEngineValueSnapshot(value.Right),
+			HiddenChanged: value.HiddenChanged,
+		}
+	}
+	return differences, nil
+}

docs/adr/0010-effective-configuration-diff.md

@@ -0,0 +1,99 @@
+# ADR 0010: Compare Frozen Effective Configuration Snapshots
+
+## Status
+
+Accepted and implemented. The
+[configuration contract](../config.md#effective-configuration-diffs) owns current
+behavior. Completed planning and remediation records are preserved in Git
+history at `1c2610c` under `docs/roadmap/`.
+
+## Date
+
+2026-10-09
+
+## Context
+
+Applications need to inspect how two completed configurations differ, including
+the effective impact of an overlay after defaults and application resolution.
+ConfigKit already retains canonical typed inspection snapshots, semantic paths,
+presence information, and sensitivity classification for successful loads.
+
+Extending this inspection model lets applications share configuration comparison
+and safe disclosure while keeping their presentation and domain interpretation.
+The operation should follow ConfigKit's existing equality, ownership, and secret
+boundaries so consumers can reason about loading and inspection consistently.
+
+## Decision
+
+Provide structured effective-value comparison between successful results of the
+same configuration type. Compare their retained canonical inspection snapshots
+through the root-owned public facade. Each comparison uses the completed load
+state and returns detached records with a semantic path and safe left and right
+value snapshots.
+
+Use canonical value equality and the existing structural comparison rules.
+Mappings compare recursively, sequences report atomic changes, and scalar or
+kind replacements report the affected region. Presence distinguishes additions
+and removals from explicit null. Equal effective values produce an empty diff;
+source attribution, explicit-input status, and history remain separately
+inspectable through each result. Canonical pointer ordering makes reporting
+deterministic.
+
+Detect changes before masking values. Apply sensitivity from both loads to both
+returned sides, including historical and dependency-derived classification.
+Preserve public content where the shapes permit corresponding sensitive regions
+to be identified. When a structural replacement prevents safe correspondence,
+mask the complete reported replacement region on both present sides. Absence
+retains its own representation.
+
+Keep masking and hidden-change information distinct. Each record indicates
+whether an actual change is withheld by redaction, allowing applications to
+display a changed-sensitive-value indicator even when safe snapshots render
+identically. Public-only changes alongside unchanged masked content retain that
+distinction.
+
+Typed secret references participate through their configured environment names.
+Resolved credential bytes remain behind the existing explicit secret accessor.
+The comparison uses the same frozen inspection boundary as effective rendering
+and explanation.
+
+ConfigKit owns comparison and paired safe disclosure. Applications own labels,
+layout, and rendering of the returned changed regions. Reusing the existing
+snapshot representation and engine boundary keeps the extension consistent with
+the library's established inspection model.
+
+## Alternatives considered
+
+- **Compare input text or separately rendered YAML.** Supports familiar textual
+  displays, but input text precedes composition and resolution, and independently
+  redacted output can hide changes or apply different disclosure rules. Canonical
+  comparison with paired masking represents the completed configuration.
+- **Leave comparison to applications using returned Go values.** Offers direct
+  access to application types, but duplicates structural and redaction machinery
+  and observes caller mutation. Retained inspection snapshots preserve the
+  completed load's values and established ownership boundary.
+- **Align sequence elements and return context-rich rendering data.** Enables
+  finer-grained displays, but requires additional correspondence and disclosure
+  rules. Atomic sequence records and existing value snapshots satisfy the
+  selected changed-region workflows with a smaller public model.
+- **Compare resolved credentials or retain credential-derived tokens.** Could
+  detect rotation behind an unchanged reference, but expands retained sensitive
+  state and introduces a separate trusted comparison mechanism. Reference-name
+  comparison preserves the existing inspection boundary.
+
+## Consequences
+
+Applications can compare independently loaded configurations using ConfigKit's
+shared equality, presence, and disclosure rules. Existing composition and load
+semantics continue to determine the values being compared. Caller mutation of a
+returned configuration leaves its retained comparison snapshot unchanged.
+
+Paired redaction can conceal public content within a structurally incompatible
+replacement. The changed region and hidden-change indicator still communicate
+its effective impact. Credential rotation behind an unchanged environment name
+produces equal reference values for comparison.
+
+The implementation requires operation-local disclosure preparation and focused
+coverage for presence, shape changes, historical sensitivity, and detached
+results. Applications retain control of presentation; changed-region records
+supply the safe data needed for that responsibility.

docs/config.md

@@ -423,6 +423,46 @@ an explicit `LoadSecretsDir` bootstrap, then use `WriteDiagnostics`,
 ConfigKit does not infer bootstrap outcomes from a secret reference and does not
 bundle these independent reports into a command framework.
 
+## Effective configuration diffs
+
+`configkit.Diff(left, right)` compares two completed successful loads of the same
+configuration type. `left` is the earlier state and `right` is the later state.
+Applications load both sides with the sources and options they choose; to inspect
+an overlay's impact, load the same base once without the overlay and once with it
+selected. The [consumer guide](consumers/README.md#effective-configuration-diffs)
+links to maintained examples. The public API returns safe changed-region records;
+applications own their presentation.
+
+Comparison uses the frozen canonical effective inspection values, not mutable
+`Result.Config`, source text, provenance, or history. It does not reopen sources,
+reread environment variables, or rerun defaults or callbacks. Equal effective
+values produce no records even when sources, explicit-input status, defaults, or
+resolution histories differ; for example, explicit zero and defaulted zero are
+equal. Mappings compare recursively, sequences compare atomically, and scalar,
+kind, or null/container replacements report their affected region. Records use
+the existing comparator's canonical pointer ordering. `Present=false` with empty
+YAML means absence; explicit null is present and renders as `null`.
+
+Before either side is returned, sensitivity from both loads is applied to both
+snapshots, including historical and dependency-derived classification. A
+classification on either side protects the corresponding values on both sides.
+`Redacted` reports masking, while `HiddenChanged` reports an actual concealed
+value or presence change; it is not implied merely by redaction. A structural
+replacement that prevents safe correspondence masks the complete reported
+region, and an absent side remains absent. Record membership establishes that a
+change occurred even when safe snapshots render identically. Literal
+marker-looking input is ordinary input; consumers use the record fields rather
+than interpreting marker text.
+
+Typed secret references contribute their configured environment names to the
+frozen comparison, never resolved credential bytes. Credential rotation behind
+an unchanged reference is therefore not detected. The records contain changed
+regions only, not paired full-document context; independently calling
+`WriteEffective` on each result does not create cross-protected context. Nil or
+uninitialized results return an error with no records. A failed `Load` retains
+its normal nil-result/`LoadError` behavior, which callers handle before invoking
+`Diff`.
+
 ## Typed secret references
 
 Credential-bearing fields use the opaque `Secret` type and store an environment

docs/consumers/README.md

@@ -18,6 +18,7 @@ sanitized shapes using only ConfigKit and the Go standard library:
 | Bundled file | Simple native `fs.FS` source through ordinary `Load` | Selection and lifetime of the application-owned embedded filesystem |
 | Layered catalog | Embedded defaults with an import, a mapping underlay, an independent host main file, explicit false/zero input, and source-relative resource access | Domain validation and opening/interpreting the template resource |
 | Named presets | One-load sibling inheritance, explicit false, nested destination resolution, and source/derivation inspection | Choosing and executing a preset |
+| Effective configuration diff | Same-type frozen effective comparisons for two selected files or base-versus-overlay impact | Source/options selection and consumer-owned safe presentation |
 
 The YAML under [`testdata`](../../examples/consumers/testdata) is loaded by the
 executable examples and ordinary tests. It contains no private application data,
@@ -51,6 +52,25 @@ both without redefining their syntax. ConfigKit overlays are configuration overl
 they do not select or replace an application's LLM, model, pipeline, report, or
 execution profile concepts.
 
+## Effective configuration diffs
+
+[`CompareFiles`](../../examples/consumers/diff.go) loads two caller-selected files
+with one application definition, handles each load error, calls `configkit.Diff`,
+and presents the safe records through consumer-owned `FormatDifferences`.
+[`CompareRolloutOverlay`](../../examples/consumers/diff.go) loads the same base
+once without an overlay and once with the selected overlay, so omitted lower
+priority values remain present. Its resolver records a derived endpoint URL after
+overlay application, and its nested typed secret reference is classified before
+the resulting records are presented.
+
+The maintained [behavior tests and executable examples](../../examples/consumers/diff_test.go)
+use temporary files and disposable secret values. Presenters should use
+`ValueSnapshot.Present` for absence, record membership for change, and
+`HiddenChanged` for a withheld change indicator. Do not parse the redaction marker
+or add separately rendered full contexts that lack combined sensitivity. The
+[configuration contract](../config.md#effective-configuration-diffs) owns shared
+equality, granularity, and disclosure semantics.
+
 ## Named sibling inheritance
 
 [`LoadPresets`](../../examples/consumers/inheritance.go) loads the maintained
@@ -168,6 +188,7 @@ focused behavioral owner:
 | `LoadSecretsDir`, bootstrap reporting, typed lookup, CLI explanation | `Example_weatherStartup` |
 | Native filesystem, grouped underlays, programmatic mapping, retained resource context | `Example_nativeFilesystem`, `Example_layeredCatalog`, and their focused consumer tests |
 | Named sibling inheritance, presence, and derivation | `Example_inheritedPresets` and `TestPresetCatalogOneLoadAndDerivation` |
+| Effective configuration diffs and consumer-owned presentation | `ExampleDiff`, `ExampleCompareFiles`, and `ExampleCompareRolloutOverlay` |
 | Results, metadata, diagnostics, effective output, and writer failures | Focused root-package load, provenance, rendering, and explanation tests |
 
 The package-level import-boundary test covers the consumer examples too: supported

docs/development.md

@@ -54,6 +54,7 @@ Accepted decisions:
 - [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)
+- [Compare frozen effective configuration snapshots](adr/0010-effective-configuration-diff.md)
 
 For cross-cutting changes, follow every applicable row. Completed implementation
 and remediation plans are preserved in Git history at `cb5b435`; use current
@@ -64,8 +65,9 @@ git show cb5b435:docs/roadmap/remediation.md
 ```
 
 Release-candidate, publication, and verification work follows the operational
-[release procedure](release.md). Its single publication command validates the
+[release procedure](release.md). Its module-selected ReleaseKit `publish`
-committed candidate and publishes only the intended refs.
+invocation validates the committed candidate and publishes only the intended
+tag; those release checks remain distinct from the everyday development check.
 
 The completed string-and-integer schema-version implementation and remediation
 records are preserved in Git history at `244104f`. The
@@ -93,9 +95,27 @@ 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
+The completed ReleaseKit adoption, startup performance request and experiments,
-dependencies explicitly before entering an offline development or validation
+benchmark evidence, performance audit, implementation plan, and remediation
-environment:
+record are preserved in Git history at `8e91a2b` under `docs/roadmap/`. For example:
+
+```sh
+git show 8e91a2b:docs/roadmap/startup-benchmark.md
+```
+
+Remaining optimization candidates belong to
+[deferred scope](roadmap/deferred.md#deferred-performance-experiments).
+
+The completed effective-configuration diff roadmap, implementation plan, and
+resolved review findings are preserved in Git history at `1c2610c` under
+`docs/roadmap/`. The
+[configuration contract](config.md#effective-configuration-diffs) owns current
+comparison and disclosure behavior, and
+[ADR 0010](adr/0010-effective-configuration-diff.md) records the decision.
+
+Install the Go version required by `go.mod` or a compatible newer toolchain.
+Acquire declared dependencies explicitly before entering an offline
+development or validation environment:
 
 ```sh
 go mod download
@@ -125,11 +145,10 @@ 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 [publication command](release.md#4-publish-the-committed-candidate) invokes
+The [release procedure](release.md#4-publish-the-committed-candidate) performs
-the release checker once. It performs one minimum-toolchain offline race-suite
+its selected validation through one `publish` invocation. The everyday checker
-run, one full vet pass, and Linux cross-builds using readonly module mode.
+remains a development gate and is not a separate release prerequisite. CI never
-It already covers examples, links, and package boundaries; do not additionally
+gates a release.
-run the everyday checker just to repeat those checks. CI never gates a release.
 
 ## Task-to-test map
 
@@ -150,12 +169,13 @@ code changes. Use the component overview to find the corresponding implementatio
 | 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'` |
 | Passive resource contexts | [Engine contexts](../internal/engine/resource_context_test.go), [public contexts](../facade_resource_context_test.go) | `go test ./internal/engine -run 'Resource'` and `go test . -run 'SourceContext'` |
 | 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'` |
+| Effective configuration diff | [Engine comparison and masking tests](../internal/engine/diff_test.go), [engine operation tests](../internal/engine/diff_operation_test.go), [root facade tests](../facade_diff_test.go), and [consumer examples](../examples/consumers/diff_test.go) | `go test ./internal/engine -run 'Diff|Explain|History|Secret|Independent'`, `go test . -run 'Diff|FacadeInspection|PublicFacadeBoundary|DependencyImportBoundary'`, `go test ./examples/consumers`, and `go test . -run '^ExampleDiff$'` |
 | Consumer examples and migration fixtures | [Consumer tests](../examples/consumers/consumers_test.go), [native and layered examples](../examples/consumers/layered_test.go), [API examples](../example_test.go) | `go test ./examples/consumers` and `go test . -run '^Example'` |
 | Assembly and layered scaling evidence | [Assembly benchmarks](../internal/engine/assembly_bench_test.go), [layered benchmarks](../internal/engine/underlay_bench_test.go) | `go test ./internal/engine -run '^$' -bench '^BenchmarkUnderlay' -benchmem`; repeat with `^BenchmarkCompose` and `^BenchmarkOverlay` |
 | Inheritance scaling evidence | [Expansion benchmarks](../internal/engine/inheritance_bench_test.go) | `go test ./internal/engine -run '^$' -bench '^BenchmarkInheritance' -benchmem` |
 | Documentation links and dependency isolation | [Link checks](../documentation_test.go), [import boundary](../import_boundary_test.go), [public boundary](../public_boundary_test.go) | `go test . -run 'TestLocalDocumentationLinks\|TestDependencyImportBoundary\|TestPublicFacadeBoundary'` |
-| Development and release checker behavior | [Shell regression](../release_check_test.go) | `go test . -run 'TestCheckScripts\|TestDevelopmentCheck'` |
+| Development check behavior | [Development checker test](../development_check_test.go) | `go test . -run '^TestDevelopmentCheckHandlesFilenamesAndStopsOnFailure$'` |
-| Guarded release publication and recovery | [Publication regression](../release_publish_test.go) | `go test . -run '^TestReleasePublication'` |
+| Release profile wiring | [Release profile test](../releasekit_profile_test.go) | `go test . -run '^TestReleaseKitProfile$'` |
 
 ## Fuzz validation
 

docs/internal/overview.md

@@ -12,7 +12,8 @@ Implemented component owners:
   sibling inheritance before typed decoding. It also owns schema
   inspection, lifecycle coordination, callback auditing,
   provenance/history, passive source-context retention, secret resolution and
-  bootstrap, and safe inspection rendering. It never imports the root package.
+  bootstrap, safe inspection rendering, and effective-value comparison over
+  frozen inspection snapshots. It never imports the root package.
 - Root `Source`, `Filesystem`, `Input`, `Underlay`, `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;
@@ -21,6 +22,9 @@ Implemented component owners:
 - 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.
+- Root `Diff` and `Difference` provide the public comparison boundary and
+  convert detached engine records to root-owned paths and snapshots; consumer
+  examples own presentation of the safe changed regions.
 - `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, inheritance, decoding,
@@ -37,9 +41,11 @@ these constraints and rejects exported aliases, fields, or signatures involving
 internal types.
 
 The [configuration contract](../config.md) owns implemented YAML and lifecycle
-semantics. The [consumer adoption guide](../consumers/README.md) owns application
+semantics, including [effective configuration diffs](../config.md#effective-configuration-diffs).
-guidance. The [architecture policy](../policy/architecture.md) owns contributor
+The [consumer adoption guide](../consumers/README.md) owns application guidance.
-boundaries, and [ADR 0006](../adr/0006-public-facade.md) records the facade
+The [architecture policy](../policy/architecture.md) owns contributor
+boundaries; [ADR 0006](../adr/0006-public-facade.md) records the facade decision
+and [ADR 0010](../adr/0010-effective-configuration-diff.md) records the diff
 decision. See the [development guide](../development.md) for validation commands
 and [release procedure](../release.md) for source-candidate gates. [ADR
 0009](../adr/0009-sibling-inheritance.md) records why inheritance is a built-in

docs/oss/attribution.md

@@ -2,11 +2,12 @@
 
 ## Standard Repository Policies
 
-Material: `docs/policy/meta.md`, `docs/policy/oss.md`,
+Material: `docs/policy/release.md`, adapted from
+`e833faddf120c789a9b45348edaf75720de16348`; `docs/policy/meta.md`, `docs/policy/oss.md`,
 `docs/policy/documentation.md`, `docs/policy/agents.md`,
-`docs/policy/architecture.md`, `docs/policy/testing.md`, and
+`docs/policy/architecture.md`, `docs/policy/testing.md`; root `AGENTS.md`; and the
-`docs/policy/release.md`; root `AGENTS.md`; and the Policy Reading Guide in
+Policy Reading Guide in `docs/development.md`, adapted from
-`docs/development.md`, adapted for this repository.
+`d84a38ebab26f048cafbe59a2246700c35d29843` for this repository.
 
 Copyright (C) 2026 Eric Rakestraw
 
@@ -14,10 +15,14 @@ SPDX-License-Identifier: CC-BY-SA-4.0
 
 License and notices: [CC BY-SA 4.0](licenses/CC-BY-SA-4.0.txt) |
 [COPYRIGHT](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/COPYRIGHT) |
-[LICENSE](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/LICENSE).
+[LICENSE](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/LICENSE) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/policy/src/commit/e833faddf120c789a9b45348edaf75720de16348/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/policy/src/commit/e833faddf120c789a9b45348edaf75720de16348/LICENSE).
 
 [Source](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843).
 
+[Source](https://gitea.maximumdirect.net/eric/policy/src/commit/e833faddf120c789a9b45348edaf75720de16348).
+
 ## go-yaml v4
 
 Selected module: `go.yaml.in/yaml/v4` at `v4.0.0-rc.6`.

docs/policy/architecture.md

@@ -201,6 +201,13 @@ See [ADR 0005](../adr/0005-explicit-overrides-and-safe-explanation.md).
 Detailed syntax and operation tables belong to the
 [current configuration contract](../config.md).
 
+The frozen inspection boundary also supports comparing completed same-type
+results without reopening sources or rerunning the load lifecycle. The
+[configuration contract](../config.md#effective-configuration-diffs) owns
+comparison and disclosure behavior, the [component overview](../internal/overview.md)
+owns implementation responsibility, and [ADR 0010](../adr/0010-effective-configuration-diff.md)
+records the accepted decision.
+
 ## Ownership And Confidentiality
 
 Returned configuration and metadata must not share mutable state across loads.

docs/policy/release.md

@@ -1,10 +1,10 @@
 # Release Policy
 
-**Base Policy Version:** 1.4
+**Base Policy Version:** 1.6
 
-**Last Updated**: 2026-09-28
+**Last Updated**: 2026-10-09
 
-**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/release.md)
+**Upstream Source:** [Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy/src/commit/e833faddf120c789a9b45348edaf75720de16348/docs/policy/release.md)
 
 ## Purpose
 
@@ -12,6 +12,9 @@ This policy defines a proportionate workflow for validating and publishing an
 intended source revision under a fresh version. Releases should require little
 routine intervention, avoid repeated work, and preserve published contents.
 
+Adopt stronger verification or reproducibility requirements through an explicit
+project-specific decision justified by the intended audience and support needs.
+
 The repository-specific commands belong in `docs/release.md`. Historical release
 summaries belong in `docs/releases/`. The procedure must agree with the adopted
 policy and link to it rather than introduce additional release requirements.
@@ -54,10 +57,11 @@ authoritative primary branch, completes the release. The source commit may be
 pushed before the tag or published together with it through an atomic push.
 The procedure must choose and document the supported approach.
 
-ConfigKit uses sequential explicit pushes: first the captured candidate to
+ConfigKit uses sequential publication: first push the committed candidate to
-authoritative `main`, then the annotated tag. Its
+authoritative `main`, then invoke ReleaseKit once to validate that candidate and
-[release procedure](../release.md) names `origin` and checks that its fetch and
+publish its annotated tag. The [release procedure](../release.md) names
-push destinations resolve to the authoritative URL.
+`origin`; ReleaseKit checks its exact effective push URL before validation and
+tag publication.
 
 Release commands must finish at successful publication. They must not wait for
 or poll CI, require successful CI status, inspect downloadable artifacts, or
@@ -76,8 +80,9 @@ the tagged source. The procedure must identify those deliverables and the
 responsibility of their automation. Published deliverables must be traceable
 to that source and identify the same version.
 
-ConfigKit currently declares no additional deliverables. Its source-tag push
+ConfigKit currently declares no additional deliverables. Confirmed publication
-is the completion point.
+of the intended source tag is the completion point. CI, macOS validation,
+hosted delivery, and consumer retrieval are outside the release gates.
 
 ## Versioning And Compatibility
 
@@ -96,7 +101,8 @@ requires a deliberate update to the policy and procedure where needed.
 For releases at or after `v1.0.0`:
 
 - a major release may make intentional incompatible changes;
-- a minor release may add backward-compatible behavior; and
+- a minor release may add backward-compatible behavior or raise the Go consumer
+  minimum as described below; and
 - a patch release may make backward-compatible fixes.
 
 Before `v1.0.0`, a minor release may change a documented public, operational,
@@ -108,13 +114,53 @@ Additional compatibility promises and deliberate exceptions belong in the
 adopted policy or canonical contract documentation. Release notes explain
 changes; they do not redefine current compatibility contracts.
 
+## Consumer Minimum And Release Toolchain
+
+Distinguish the minimum toolchain supported for consumers from the toolchain
+maintainers use to build and validate a release. Record the consumer minimum in
+the language's standard metadata and explain its support meaning in canonical
+documentation. Define the selected release toolchain and its setup commands in
+`docs/release.md`. Toolchain selection and upgrade cadence are repository-specific
+choices.
+
+For Go repositories, normally declare the initial stable release of the selected
+series as the consumer minimum, such as `go 1.26.0`. Use a higher patch minimum
+when a dependency or an identified correctness fix requires it, and document
+the reason.
+
+For release-policy purposes, successful build and release validation on the
+selected Go patch release are sufficient to presume support across that Go
+series, subject to the declared consumer minimum and concrete evidence of
+incompatibility. Investigate specific compatibility concerns as they arise.
+
+Use the selected release toolchain for candidate validation and release builds,
+including CI jobs performing those tasks. A newer validation patch version alone
+leaves the consumer minimum unchanged.
+
+A minor release may raise the Go consumer minimum, including from one Go series
+to the next, both before and after `v1.0.0`. This is an explicit exception to the
+backward-compatibility requirement for minor releases. Patch releases preserve
+the consumer minimum. Explain an increase's impact and required consumer action
+in the release note. Other incompatible changes remain subject to the versioning
+rules above.
+
+### ConfigKit Toolchain Selection
+
+For minor and major releases, select the newest stable Go series available in
+the development environment. For patch releases, retain the series recorded in
+`go.mod` and its consumer minimum. Use the latest locally available compatible
+patch in the selected series, with `GOTOOLCHAIN=local`, to build the
+module-selected ReleaseKit CLI and validate the candidate. The same Go
+executable builds the tool and runs its validation commands.
+
 ## Release Documentation And Preparation
 
 Every new release must include `docs/releases/<version>.md` in the tagged
 source tree. Use the complete version tag as the filename and begin with a
 title containing the product name and that exact version.
 
-ConfigKit requires the first line `# ConfigKit <version>`.
+ConfigKit requires the first line `# ConfigKit <version>`. ReleaseKit's
+publication guard checks the release-note H1 for the product and version.
 
 Include a short summary and any relevant compatibility impact or upgrade
 instructions. Choose sections suited to the release and keep the note
@@ -146,10 +192,9 @@ checks publication state, and publishes the intended refs. A validation-only
 mode or command may be provided for diagnosis, but must not be a required step
 before publication repeats the same checks.
 
-ConfigKit uses `./scripts/release.sh vMAJOR.MINOR.PATCH`. The separate
+ConfigKit uses the module-selected ReleaseKit CLI's `publish
-`scripts/release-check.sh` remains an optional diagnostic command; the
+vMAJOR.MINOR.PATCH` command. Its `check` command is optional for diagnosis; it
-publication command invokes it once and does not use a persistent candidate
+is not a required preliminary pass to publication.
-record.
 
 Run the complete deterministic, offline default test suite once for the final
 candidate, following the [testing policy](testing.md). For repositories that
@@ -157,13 +202,17 @@ publish builds, verify the required build targets. Select those targets for
 the application's actual support commitments; native testing on each platform
 and access to particular hardware are not default release prerequisites.
 
-ConfigKit's one maintained Go 1.25 baseline runs the full suite with the race
+Prepare dependencies and build the tool before offline validation; the
-detector and test-time vet disabled. This protects library behavior, ownership,
+publication command is the required validation run, with no separate successful
-and concurrent use; the suite already includes examples, consumer fixtures,
+test or CI run required before it.
-documentation links, and package boundaries. One full vet pass adds static
+
-checks beyond the test-time subset. CGO-disabled Linux amd64 and arm64 builds
+The selected profile runs the complete deterministic, offline default suite
-cover supported configurations distinct from native race compilation. macOS
+once with the race detector and test-time vet disabled. The suite already
-and newer-toolchain checks are optional.
+includes examples, consumer fixtures, documentation links, and package
+boundaries. One full vet pass adds static checks beyond the test-time subset.
+CGO-disabled Linux amd64 and arm64 package compilation covers supported
+configurations distinct from native race compilation. macOS and newer-toolchain
+checks are optional.
 
 Additional gates must address a concrete risk that the existing checks do not
 adequately cover. Do not automatically require linting, race testing, module
@@ -172,9 +221,10 @@ expanded platform matrices solely because they are possible. Retain such
 checks when their distinct protection justifies their cost. A one-time migration
 check must not silently become a permanent release requirement.
 
-The selected Go commands use readonly module mode with `GOPROXY=off`; acquire
+ReleaseKit runs its selected Go commands with readonly module mode and
-the baseline toolchain and dependencies before validation. Formatting and
+`GOPROXY=off`; acquire dependencies and build the tool before candidate
-whitespace remain ordinary development checks in `scripts/check.sh`.
+validation. Formatting and whitespace remain ordinary development checks in
+`scripts/check.sh`.
 Review module tidiness when dependencies change, not as a release gate.
 
 Release tests must not require real credentials, mutable application services,
@@ -206,16 +256,19 @@ Automate the checks needed to publish the intended source under a fresh version:
   authoritative remote;
 - the worktree and index are clean on the primary release branch;
 - the source being published is the exact candidate that passed validation,
-  including its matching release note;
+  including its matching release note H1;
 - the remote primary branch can be advanced to that candidate without
   discarding remote history, and is published before the tag; and
 - the tag identifies the validated candidate and only the intended refs are
   published.
 
-ConfigKit also checks that `origin` has exactly the authoritative fetch and
+ReleaseKit checks that `origin`'s effective push URL exactly matches the
-push destination, including configured push URLs. The command checks the
+authoritative URL before candidate validation. This does not assert the
-candidate and unused version again after validation, and checks local state
+configured fetch URL or require the release-note H1 to be the first line; the
-before creating the tag. Ignored local files do not block publication.
+required `# ConfigKit <version>` first-line format remains a content rule. The
+command checks the candidate and unused version again after validation, and
+checks local state before creating the tag. Ignored local files do not block
+publication.
 
 Fetch the authoritative branch and tag state as needed for these checks.
 Do not force branch or tag updates to bypass a failed guard. Publish explicit
@@ -248,10 +301,10 @@ release without replacing its contents or reusing its version.
 ## Repository Release Procedure
 
 Maintain `docs/release.md` as a short, executable maintainer runbook. It must
-identify prerequisites, the primary branch and authoritative remote, version
+identify prerequisites, the selected release toolchain, the primary branch and
-and note preparation, one publication command with local checks and guards,
+authoritative remote, version and note preparation, one publication command with
-source-only deliverables, the successful-tag-push completion point, and
+local checks and guards, source-only deliverables, the successful-tag-push
-partial or unknown-state recovery.
+completion point, and partial or unknown-state recovery.
 
 Use copyable commands where practical. Keep optional diagnostics and consumer
 verification clearly optional. The procedure must not turn preparation work,

docs/release.md

@@ -1,7 +1,7 @@
 # ConfigKit Release Procedure
 
 This is the maintainer runbook for ConfigKit's [release policy](policy/release.md).
-ConfigKit publishes one source-only Go module. The immutable annotated tag and
+ConfigKit publishes a source-only Go module. The immutable annotated tag and
 matching checked-in release note are the deliverables; there is no binary,
 container image, generated package, or separate registry publication.
 
@@ -9,183 +9,221 @@ container image, generated package, or separate registry publication.
 
 - Module: `gitea.maximumdirect.net/eric/ConfigKit`
 - Primary branch: `main`
-- Authoritative remote: `origin`, with fetch and push destination
+- Authoritative remote: `origin`
-  `https://gitea.maximumdirect.net/eric/ConfigKit.git`
+- Authoritative push URL: `https://gitea.maximumdirect.net/eric/ConfigKit.git`
 - Tags: stable Semantic Versions such as `v0.5.0`; no prereleases
-- Minimum Go line: Go 1.25, validated with one maintained patch
+- Minimum Go version: the first stable patch of the selected Go series, or a
+  higher patch when required by a dependency or specific correctness fix, as
+  recorded in `go.mod`; see the
+  [consumer minimum policy](policy/release.md#consumer-minimum-and-release-toolchain)
 - Release-gated targets: Linux amd64 and arm64
 - Best-effort targets: macOS amd64 and arm64, under the
   [platform support policy](policy/release.md#platform-support)
 
-The checker runs one offline race suite, one full vet pass, and CGO-disabled
+Release validation runs one offline race-enabled Go suite, one full vet pass,
-builds for both Linux targets. It reports skipped filesystem cases. macOS checks
+and CGO-disabled package compilation for both Linux targets. macOS and CI are
-and newer-toolchain tests are optional. CI is never a readiness or completion
+not release gates; do not wait for or poll CI.
-gate; do not wait for or poll it.
 
-## 1. Prepare access and tools
+## 1. Select Go and prepare the tool
 
-Use a clean checkout with Git, Bash 3.2 or newer, a maintained Go 1.25 patch,
+Use a clean checkout with Git, Bash 3.2 or newer, and a native compiler for race
-and a native compiler for race tests. Configure private-host access through the
+tests. Choose the release type before selecting Go. For a minor or major release,
-normal credential manager. Keep credentials and environment dumps outside the
+select the newest stable Go series available in the development environment.
-repository and command transcript.
+For a patch release, retain the series recorded in `go.mod` and leave its consumer
+minimum unchanged. Follow the
+[toolchain selection policy](policy/release.md#configkit-toolchain-selection).
 
-Verify access without displaying credentials:
+Put the selected series' latest locally available compatible patch first on
+`PATH`, ensuring it meets `go.mod`'s minimum. The same `go` executable must build
+ReleaseKit and run its child validation commands. Set local toolchain selection
+and verify it:
 
 ```sh
-git remote get-url origin
+export GOTOOLCHAIN=local
-git ls-remote origin HEAD
+go version
+go env GOVERSION
+command -v go
 ```
 
-The fetch URL and all configured push destinations must resolve to the
+Only when a minor or major release advances the consumer minimum to a newer Go
-authoritative URL above. The publication command checks this again. Acquire the
+series, derive that series' initial stable release from the selected executable:
-selected toolchain and dependencies explicitly before offline validation:
 
 ```sh
-export CONFIGKIT_BASELINE_TOOLCHAIN=go1.25.14
+selected_go=$(GOTOOLCHAIN=local go env GOVERSION)
-GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go version
+selected_series=${selected_go#go}
-GOTOOLCHAIN="$CONFIGKIT_BASELINE_TOOLCHAIN" go mod download
+selected_series=${selected_series%.*}
+release_minimum="$selected_series.0"
+go mod edit -go="$release_minimum"
 ```
 
-A maintained patch may replace the example pin. No per-release latest-version
+If a dependency or identified correctness fix requires a higher patch minimum,
-survey is required. Dependencies must be cached; the checker sets `GOPROXY=off`.
+use that required version instead and document the reason. When the series is
-Publication requires user authorization. Standing authorization for local
+unchanged, leave the minimum unchanged unless a minor or major release
-commits does not authorize a push or release.
+deliberately changes it under the
+[consumer minimum policy](policy/release.md#consumer-minimum-and-release-toolchain).
+For example, validating with Go 1.26.8 leaves `go 1.26.0` unchanged. There is no
+separate requirement to validate with Go 1.26.0.
 
-## 2. Select the version and review compatibility
+Prepare dependencies whether or not the minimum changes:
 
-Choose an unused stable version. Compare the candidate with the previous tag.
+```sh
-Review exported Go signatures and ownership, YAML and scalar semantics,
+go mod download
-precedence, diagnostic codes, minimum Go version, and platform support. A
+```
-signature-preserving change may still affect consumers. Before `v1.0.0`,
-intentional incompatible minor-release changes need a note explaining impact
-and consumer action; patch releases remain compatible within their minor line.
-Review the maintained consumer examples and migration guide.
 
-When dependencies change, review parser behavior and migration impact as part
+Build the tool selected by `go.mod` into temporary storage outside the checkout.
-of that change. Module tidiness belongs to dependency-change review, not the
+Ensure `$TMPDIR` names a system temporary location, not the repository. These
-release checker. Do not repeat a dependency-version survey for every release.
+commands never install another ReleaseKit version:
 
-## 3. Write and commit the release note
+```sh
+releasekit_tmp=$(mktemp -d "${TMPDIR:-/tmp}/configkit-releasekit.XXXXXX")
+releasekit_bin="$releasekit_tmp/releasekit"
+go build -o "$releasekit_bin" gitea.maximumdirect.net/eric/ReleaseKit/cmd/releasekit
+go list -m gitea.maximumdirect.net/eric/ReleaseKit
+"$releasekit_bin" version
+```
 
-Create `docs/releases/<version>.md` for the selected version. Its first line
+The module-selected executable is ReleaseKit v0.4.1. Use the built executable
-must be `# ConfigKit <version>`. Give a meaningful summary and include
+for publication to preserve its exit status and publication-state diagnostics.
-compatibility impact or upgrade instructions when applicable. Link to current
+`go run` maps a nonzero child exit status to 1. ReleaseKit's child Go commands
-contracts for exact behavior. Review the note and affected canonical documents
+use the `go` found on `PATH` with `GOTOOLCHAIN=local`; keep the selected
-as ordinary preparation, then commit the complete candidate.
+executable first on `PATH` through the publication command.
 
-End every new note with these links, replacing `VERSION` with the complete tag:
+Verify access to the authoritative remote without displaying credentials:
+
+```sh
+git ls-remote https://gitea.maximumdirect.net/eric/ConfigKit.git HEAD refs/heads/main
+```
+
+Publication requires explicit authorization. Local implementation commits do
+not authorize a push or release.
+
+## 2. Prepare and commit the candidate
+
+Choose an unused stable version locally and on the authoritative remote. Compare
+the candidate with the previous tag and review exported Go signatures and
+ownership, YAML and resolution semantics, diagnostic contracts, minimum Go
+version, and platform support. Review maintained consumer examples and the
+migration guidance. Explain any consumer-minimum increase and required consumer
+action under the
+[consumer minimum policy](policy/release.md#consumer-minimum-and-release-toolchain).
+
+Create `docs/releases/<version>.md`. Its first line must be exactly
+`# ConfigKit <version>`, and it must end with the license and attribution footer:
 
 ```markdown
 [COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/VERSION/docs/oss/attribution.md)
 ```
 
-Confirm the three target files exist in the candidate and review the version in
+Replace `VERSION` with the full tag and confirm the three target files exist in
-the URLs. The future tag need not resolve remotely yet; this review adds no
+the candidate. Retire completed roadmaps, preserve unfinished and deferred
-network gate. ConfigKit uses checked-in notes without hosted release objects.
+work, and repair affected links. Review the complete candidate for unintended
-If a hosted page is used later, reuse the note and preserve its footer. Do not
+files and credentials, then commit it on `main`. These are ordinary preparation
-rewrite historical notes or add downloadable license assets.
+tasks, not separate approval gates. Any `go.mod` change belongs in this
+candidate.
+
+## 3. Push the candidate to `main`
+
+Push only that committed candidate to the literal authoritative URL. This does
+not follow local tags:
+
+```sh
+git push --no-follow-tags https://gitea.maximumdirect.net/eric/ConfigKit.git HEAD:refs/heads/main
+```
+
+ReleaseKit requires authoritative `main` to equal this candidate before it
+validates. A failure before this push means ReleaseKit publication has not
+started. If the push result is uncertain, inspect authoritative `main` and
+continue only when it is confirmed at the candidate. If validation later fails,
+no release tag is published; correct the issue in a new commit, push the new
+candidate to `main`, and invoke validation again.
 
 ## 4. Publish the committed candidate
 
-Before publication, review compatibility, release-note accuracy, and the file
+With the authorized candidate already on authoritative `main`, invoke the
-list for unintended content or credentials. Retire completed roadmaps as part of
+module-selected native executable exactly once:
-release preparation, preserving unfinished and deferred work and repairing
-links. These are ordinary preparation tasks, not separate human sign-offs.
-
-With the release explicitly authorized, run the one publication command.
-The script resolves the repository root from its own path, so it may be invoked
-from another directory by using its path there. Replace the sample version with
-the selected version:
 
 ```sh
-./scripts/release.sh v0.5.0
+"$releasekit_bin" publish vMAJOR.MINOR.PATCH
 ```
 
-The command requires `main`, a clean index/worktree, an unused version locally
+Replace the placeholder with the selected version. ReleaseKit checks the
-and on the authoritative remote, and a matching note in the captured commit.
+effective push URL against `expected_push_url`, verifies the candidate on
-Ignored local files do not block it. It checks remote ancestry, runs
+`main`, and checks the release-note H1 for the product and version. It then
-[`release-check.sh`](../scripts/release-check.sh) once against that commit,
+runs the selected race-enabled standard suite once with test-time vet disabled,
-rechecks candidate and version state, pushes only that commit to `main`, then
+one full vet pass, and CGO-disabled package compilation for Linux amd64 and
-creates and pushes one annotated tag. The tag message is the checked-in note.
+arm64. It publishes only the annotated tag for that candidate. Confirmed
-It never commits or repairs the checkout.
+publication of the intended tag completes the release. The tag points to the
-
+captured commit and uses the complete checked-in note as its annotation message.
-A successful intended tag push completes publication. The command reports the
+The optional `check`
-version and commit immediately. No CI, module retrieval, remote read-back, or
+command is available for diagnosis but is not a separate required pass:
-hosted release object is required. The checker may be run separately for
-diagnosis, but it is not a prerequisite: a fresh publication invocation
-validates its candidate once.
-
-## 5. Recover from a failed or uncertain push
-
-The command performs one bounded authoritative-state check after a failed push.
-If the main push failed but authoritative main equals the candidate, it proceeds.
-If the tag push failed but its exact tag object reached the remote, it reports
-success. Otherwise it reports branch-only, conflicting, or unknown state and
-retains any local tag.
-
-Inspect exact refs before any retry. Set `release_version` to the attempted
-version and compare main with the candidate from the command's report:
 
 ```sh
-release_version=v0.5.0
+"$releasekit_bin" check vMAJOR.MINOR.PATCH
-authoritative=https://gitea.maximumdirect.net/eric/ConfigKit.git
-if remote_main=$(git ls-remote --refs --exit-code "$authoritative" refs/heads/main); then
-  printf 'remote main: %s\n' "$remote_main"
-else
-  result=$?
-  if [ "$result" -eq 2 ]; then
-    printf 'authoritative main confirmed absent\n' >&2
-  else
-    printf 'remote main state unknown; inspect before retrying\n' >&2
-  fi
-fi
-ref="refs/tags/$release_version"
-if remote_tag=$(git ls-remote --refs --exit-code "$authoritative" "$ref"); then
-  printf 'remote tag: %s\n' "$remote_tag"
-else
-  result=$?
-  if [ "$result" -eq 2 ]; then
-    printf 'remote tag confirmed absent\n'
-  else
-    printf 'remote tag state unknown; do not reuse the version\n' >&2
-  fi
-fi
-if local_tag=$(git rev-parse --verify "refs/tags/$release_version" 2>/dev/null); then
-  printf 'local tag object: %s\n' "$local_tag"
-else
-  printf 'no local tag object\n'
-fi
 ```
 
-A query failure is not proof that the tag is absent. Compare the remote tag
+Status 0 confirms publication, status 1 reports a known publication failure or
-object ID with the local annotated tag object ID; its peeled commit alone is
+conflict, status 2 reports usage, profile, or version errors, and status 3 means
-insufficient to establish identical publication. A conflicting published tag
+the push outcome remains unknown. Preserve both the native exit status and its
-must not be moved or replaced. If remote main advanced but the tag was not
+diagnostics.
-published, report that partial progress. Only after confirming the local tag
+
-was never published or used by another channel may a maintainer remove it:
+The command does not push or repair `main`, wait for CI, or publish binaries or
+a hosted release page. A successful intended-tag publication does not require
+remote read-back or consumer retrieval; those checks remain optional.
+
+## 5. Recover from a failed or uncertain tag push
+
+The executable reports the publication state, phase, version, candidate commit,
+tag-object ID, effective endpoint, and error on standard error. It performs one
+bounded authoritative reconciliation after a failed tag push. Exit status 3
+means the tag outcome remains unknown; do not blindly retry or move a tag.
+
+For an uncertain result, use the exact endpoint, candidate commit, version, and
+tag-object ID from the report. Copy the captured endpoint into the variable
+below using normal shell quoting. Check that Git still resolves it to itself,
+then query the authoritative refs once:
+
+```sh
+authoritative='COPY_CAPTURED_ENDPOINT'
+release_version='vMAJOR.MINOR.PATCH'
+test "$(git ls-remote --get-url -- "$authoritative")" = "$authoritative" &&
+  git ls-remote --refs -- "$authoritative" refs/heads/main "refs/tags/$release_version"
+```
+
+A failed URL-equality check or remote query leaves the outcome unresolved.
+Correct transport configuration before continuing; a rewritten destination
+cannot establish absence at the captured endpoint.
+
+Compare the `main` object ID with the reported candidate commit and the tag
+object ID with the reported tag-object ID. `--refs` returns the annotated tag
+object itself, not merely its peeled commit. If the tag object matches, the
+release is published. If the query fails, the result is conflicting, or the
+endpoint or candidate differs, stop and resolve the state before retrying. If
+the endpoint is reachable, the tag is confirmed absent, and `main` still equals
+the reported candidate, remove a retained local tag only after confirming it
+was not published or used by another channel; then rerun `publish`, which
+revalidates the candidate:
 
 ```sh
 git tag -d "$release_version"
+"$releasekit_bin" publish "$release_version"
 ```
 
-A subsequent invocation revalidates the candidate; a correctly published tag
+A validation failure after the candidate reached `main` leaves an untagged
-needs no rerun. Do not roll back main or automatically delete a tag. Transport
+candidate there. Correct it with a new commit rather than rewriting or rolling
-or authentication failure alone does not require a new version. A defect in
+back `main`. A conflicting published tag must never be moved or reused. A
-published source requires a corrected commit, a new semantically appropriate
+defect in published source requires a corrected commit, a new semantically
-version and note, and the release procedure again.
+appropriate version, and a matching release note.
 
 ## 6. Optional consumer verification
 
-Only when useful or requested, read back the remote tag or retrieve the exact
+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
+version into a new module without a local `replace` directive. These checks are
-are optional and non-gating. Do not poll CI or wait for module propagation.
+optional and non-gating. Do not poll CI or wait for module propagation. For
-Private-host credentials must already be configured. For direct-origin
+direct-origin verification, use the exact published version in a temporary
-verification, set the version to the release just published (replace the sample
+consumer module:
-below), then use a temporary consumer module and check the exact module path
-and version reported by `go list -m`:
 
 ```sh
-release_version=v0.5.0
+release_version=vMAJOR.MINOR.PATCH
 consumer_dir=$(mktemp -d)
 (
   cd "$consumer_dir"

docs/releases/v0.6.0.md

@@ -0,0 +1,63 @@
+# ConfigKit v0.6.0
+
+This minor release reduces avoidable configuration-loading and inspection work,
+adopts ReleaseKit for source publication, and raises the consumer Go minimum to
+1.26.0. The public configuration model remains unchanged from v0.5.0.
+
+## Changes
+
+- Reduce temporary path allocations by sizing pointer-formatting buffers,
+  combining final metadata traversal, reusing parsed sensitivity paths, and
+  avoiding path construction when detecting inheritance. Effective and
+  historical metadata indexes retain independently owned paths.
+- Replace repeated resolution-coverage, metadata-update, CLI-overlap, and
+  sensitivity-propagation scans with private indexes and incremental processing.
+  Preserve diagnostic ordering, history, contextual path shapes, and redaction.
+- Make presence-only metadata queries avoid materializing provenance. Prepare
+  resolution replay descriptors and immutable mapping and inheritance-history
+  lookups for inspection, and use ordered membership indexes for provenance
+  collections. Returned records remain detached; explanations still replay
+  complete trees and render on demand.
+- Add a maintained public-API startup construction benchmark. The initial path
+  formatting and metadata traversal experiments reproduced allocation reductions
+  across local and downstream workloads. Later algorithmic improvements were
+  validated behaviorally without a new benchmark campaign. Busy-host timings
+  were inconclusive; no fixed speedup or allocation threshold is promised.
+- Replace ConfigKit-owned release scripts with a small profile and the
+  module-selected ReleaseKit v0.3.0 tool. The
+  [release procedure](../release.md) documents candidate preparation, tag-only
+  publication, and failed-push recovery. Existing release checks and the
+  successful-tag-push completion point remain unchanged; CI is not a gate.
+- Adopt release policy 1.6, distinguishing the consumer Go minimum from the
+  validation toolchain. Retire completed planning and measurement records into
+  Git history while preserving [deferred work](../roadmap/deferred.md).
+
+## Compatibility and upgrade
+
+The consumer minimum increases from Go 1.25.0 to **Go 1.26.0**. Install Go 1.26.0
+or newer before upgrading, and update application build and CI environments that
+still use Go 1.25. The `go.mod` directive records the consumer minimum; using a
+newer validation patch does not itself raise that minimum. See the
+[consumer minimum policy](../policy/release.md#consumer-minimum-and-release-toolchain).
+
+Select this version and rebuild:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.6.0
+```
+
+No application-code or configuration migration is required from v0.5.0. Public
+Go signatures, strict within-tier composition, recursive tier precedence,
+sibling inheritance, presence/null distinctions, provenance, secret handling,
+and synchronous completion retain their existing contracts. See the
+[configuration contract](../config.md) and
+[consumer guide](../consumers/README.md).
+
+The YAML dependency remains `go.yaml.in/yaml/v4 v4.0.0-rc.6`. ReleaseKit is a
+declared Go tool dependency for maintainer commands, not a library runtime
+import; its requirements participate in ConfigKit's module graph. Linux amd64
+and arm64 remain release-validated targets, and macOS remains best-effort.
+Maintainers should use the current release procedure instead of the retired
+`scripts/release.sh` and `scripts/release-check.sh` commands.
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.6.0/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.6.0/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.6.0/docs/oss/attribution.md)

docs/releases/v0.7.0.md

@@ -0,0 +1,58 @@
+# ConfigKit v0.7.0
+
+This minor release adds structured comparison of completed configurations.
+Applications can inspect changes between two configuration files or the
+effective impact of a selected overlay, with ConfigKit handling comparison and
+safe value disclosure while applications own presentation.
+
+## Changes
+
+- Add `Diff[T](left, right *Result[T]) ([]Difference, error)` through the public
+  facade. It compares frozen effective inspection values from successful loads,
+  including defaults and recorded application resolution, rather than source
+  text or later mutations of `Result.Config`.
+- Return detached changed-region records containing a semantic path, safe left
+  and right `ValueSnapshot` values, and `HiddenChanged`. Mappings compare
+  recursively, sequences report atomic changes, and records follow canonical
+  pointer order. Presence distinguishes additions and removals from explicit
+  null; equal effective values produce no records regardless of provenance or
+  loading history.
+- Protect both snapshots with sensitivity from both loads, including historical
+  and dependency-derived classification. Compatible regions retain public
+  siblings; incompatible structural replacements use complete-region masking
+  where required. `HiddenChanged` identifies actual changes withheld by masking,
+  rather than merely indicating that a snapshot contains redacted content.
+- Preserve visible public scalar changes when only historical sensitive
+  descendants remain, including additions and removals. Historical explanation
+  redaction and masking of incompatible present shapes remain intact.
+- Add maintained file-comparison and base-versus-overlay examples with
+  consumer-owned formatting, plus an executable public API example. See the
+  [consumer guide](../consumers/README.md#effective-configuration-diffs) and
+  [configuration contract](../config.md#effective-configuration-diffs).
+
+## Compatibility and upgrade
+
+No application-code or configuration migration is required from v0.6.0.
+Adopting the new API is optional. Loading, composition, inheritance, provenance,
+existing inspection, and secret-handling contracts remain unchanged.
+
+Load both configurations successfully before calling `Diff`; nil or
+uninitialized results return an error with no records. Comparison does not
+reopen sources, rerun callbacks, or reread environment variables. Typed secret
+references compare by configured reference name, not resolved credential bytes,
+so credential rotation behind an unchanged name is not reported. Returned
+snapshots describe changed regions, not cross-protected full-document context.
+
+Select this version and rebuild:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.7.0
+```
+
+The consumer minimum remains Go 1.26.0. The YAML dependency remains
+`go.yaml.in/yaml/v4 v4.0.0-rc.6`, and the maintainer tool dependency remains
+ReleaseKit v0.3.0. Linux amd64 and arm64 remain release-validated targets;
+macOS remains best-effort. Publication follows the existing
+[release procedure](../release.md).
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/docs/oss/attribution.md)

docs/releases/v0.7.1.md

@@ -0,0 +1,22 @@
+# ConfigKit v0.7.1
+
+This patch updates the maintainer release tool to ReleaseKit v0.4.1. ConfigKit's
+runtime behavior and public API are unchanged.
+
+## Compatibility and upgrade
+
+No application-code or configuration migration is required from v0.7.0. The
+consumer minimum remains Go 1.26.0, and the YAML dependency is unchanged.
+
+Select this version and rebuild:
+
+```sh
+go get gitea.maximumdirect.net/eric/ConfigKit@v0.7.1
+```
+
+ReleaseKit v0.4.1 is a maintainer tool dependency and does not change consumer
+configuration or runtime behavior. Linux amd64 and arm64 remain
+release-validated targets; macOS remains best-effort. Publication follows the
+existing [release procedure](../release.md).
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.1/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.1/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.1/docs/oss/attribution.md)

docs/roadmap/deferred.md

@@ -23,12 +23,35 @@ The following remain deliberately excluded:
 - automatic schema migrations;
 - hot reload, runtime resource replacement, and remote resource validation;
 - a bundled CLI framework or application commands; and
-- configuration diffs and fingerprints.
+- configuration fingerprints.
 
 Applications may build their own validate, effective-value, source, bootstrap, and
 explanation commands around the library. Broadening these boundaries requires
 concrete consumer evidence, compatibility review, and an explicit design change.
 
+Effective configuration diffs are implemented over frozen successful-load
+inspections; their current comparison and disclosure contract is in the
+[configuration contract](../config.md#effective-configuration-diffs), with
+consumer workflows in the [adoption guide](../consumers/README.md#effective-configuration-diffs).
+Fingerprints remain deferred.
+
 Built-in sibling inheritance using `extends` is implemented as described in the
 [configuration contract](../config.md#sibling-inheritance). It is distinct from
 inheritance between selected overlay files, which remains excluded above.
+
+## Deferred performance experiments
+
+The completed performance audit left these internal optimization candidates for
+separate investigation:
+
+- branch-local explanation replay instead of the current whole-tree replay;
+- redesigning the private metadata-copy handoff while preserving detached public
+  records;
+- caching schema descriptors across loads; and
+- indexing complex contributor-trace membership while preserving its equality
+  rules and compact linked traces.
+
+These are not committed implementation work. Reconsider them with evidence that
+the benefit justifies the ownership, retained-memory, or equivalence risks. The
+completed audit and implementation evidence are preserved in Git history at
+`8e91a2b` under `docs/roadmap/`.

example_test.go

@@ -30,6 +30,32 @@ func ExampleNoSource() {
 	// Output: 4 0 <nil>
 }
 
+func ExampleDiff() {
+	type Config struct {
+		Workers int `yaml:"workers"`
+	}
+	before, err := configkit.Load[Config](configkit.Mapping("before", map[string]any{"workers": 2}))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	after, err := configkit.Load[Config](configkit.Mapping("after", map[string]any{"workers": 4}))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	differences, err := configkit.Diff(before, after)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	for _, difference := range differences {
+		fmt.Printf("%s: %s -> %s\n", difference.Path.String(),
+			strings.TrimSpace(difference.Left.YAML), strings.TrimSpace(difference.Right.YAML))
+	}
+	// Output: /workers: 2 -> 4
+}
+
 func ExampleValidation_Error() {
 	type Config struct {
 		First  string `yaml:"first"`

examples/consumers/diff.go

@@ -0,0 +1,136 @@
+package consumers
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+// FileComparisonConfig is a small application-owned shape for comparing
+// caller-selected configuration files.
+type FileComparisonConfig struct {
+	Name    string         `yaml:"name"`
+	Entries map[string]any `yaml:"entries"`
+}
+
+// CompareFiles loads two caller-selected files with the same application
+// definition, then formats only the safe records returned by configkit.Diff.
+func CompareFiles(leftPath, rightPath string) (string, error) {
+	options := configkit.Options[FileComparisonConfig]{
+		Definition: configkit.Definition[FileComparisonConfig]{
+			Defaults: func() FileComparisonConfig {
+				return FileComparisonConfig{Entries: map[string]any{}}
+			},
+		},
+	}
+	left, err := configkit.Load(configkit.File(leftPath), options)
+	if err != nil {
+		return "", fmt.Errorf("load left configuration: %w", err)
+	}
+	right, err := configkit.Load(configkit.File(rightPath), options)
+	if err != nil {
+		return "", fmt.Errorf("load right configuration: %w", err)
+	}
+	differences, err := configkit.Diff(left, right)
+	if err != nil {
+		return "", err
+	}
+	return FormatDifferences(differences), nil
+}
+
+// RolloutConfig models a service endpoint whose URL is derived by the
+// application resolver and whose credential reference is classified.
+type RolloutConfig struct {
+	Service RolloutService `yaml:"service"`
+}
+
+// RolloutService contains endpoint settings and a classified credential.
+type RolloutService struct {
+	Endpoint   RolloutEndpoint   `yaml:"endpoint"`
+	Credential RolloutCredential `yaml:"credential"`
+}
+
+// RolloutEndpoint is the effective destination used by the application.
+type RolloutEndpoint struct {
+	Host string `yaml:"host"`
+	Port int    `yaml:"port"`
+	URL  string `yaml:"url"`
+}
+
+// RolloutCredential holds only a typed secret reference in configuration.
+type RolloutCredential struct {
+	Token configkit.Secret `yaml:"token" configkit:"secret"`
+}
+
+// LoadRollout loads a base file, optionally with one selected configuration
+// overlay. Resolution derives the effective URL after the overlay is applied.
+func LoadRollout(basePath, overlayName string) (*configkit.Result[RolloutConfig], error) {
+	return configkit.Load(configkit.File(basePath), configkit.Options[RolloutConfig]{
+		Overlay: overlayName,
+		Definition: configkit.Definition[RolloutConfig]{
+			Resolve: resolveRollout,
+		},
+	})
+}
+
+// CompareRolloutOverlay compares the effective base configuration with that
+// same file plus one selected overlay. It presents only safe diff records.
+func CompareRolloutOverlay(basePath, overlayName string) (string, error) {
+	base, err := LoadRollout(basePath, "")
+	if err != nil {
+		return "", fmt.Errorf("load base configuration: %w", err)
+	}
+	withOverlay, err := LoadRollout(basePath, overlayName)
+	if err != nil {
+		return "", fmt.Errorf("load overlay configuration: %w", err)
+	}
+	differences, err := configkit.Diff(base, withOverlay)
+	if err != nil {
+		return "", err
+	}
+	return FormatDifferences(differences), nil
+}
+
+func resolveRollout(configuration *RolloutConfig, resolution *configkit.Resolution) error {
+	endpoint := &configuration.Service.Endpoint
+	if endpoint.Host == "" || endpoint.Port <= 0 {
+		return nil
+	}
+	url := fmt.Sprintf("https://%s:%d", endpoint.Host, endpoint.Port)
+	if endpoint.URL != url {
+		endpoint.URL = url
+		resolution.Record(configkit.Keys("service", "endpoint", "url"),
+			configkit.ChangeNormalization, "derived endpoint URL",
+			configkit.Keys("service", "endpoint", "host"),
+			configkit.Keys("service", "endpoint", "port"))
+	}
+	return nil
+}
+
+// FormatDifferences is consumer-owned presentation. It distinguishes absence
+// through Present and reports withheld changes through HiddenChanged without
+// interpreting redaction marker text.
+func FormatDifferences(differences []configkit.Difference) string {
+	if len(differences) == 0 {
+		return "No effective changes.\n"
+	}
+	var output strings.Builder
+	for _, difference := range differences {
+		fmt.Fprintf(&output, "%s: left=%s right=%s", difference.Path.String(),
+			formatSnapshot(difference.Left), formatSnapshot(difference.Right))
+		if difference.HiddenChanged {
+			output.WriteString(" hidden-change")
+		}
+		output.WriteByte('\n')
+	}
+	return output.String()
+}
+
+func formatSnapshot(snapshot configkit.ValueSnapshot) string {
+	if !snapshot.Present {
+		return "<absent>"
+	}
+	return strconv.Quote(snapshot.YAML)
+}

examples/consumers/diff_test.go

@@ -0,0 +1,187 @@
+package consumers_test
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+	"gitea.maximumdirect.net/eric/ConfigKit/examples/consumers"
+)
+
+func ExampleCompareFiles() {
+	directory, err := os.MkdirTemp("", "configkit-diff-files-")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	defer os.RemoveAll(directory)
+	leftPath := filepath.Join(directory, "before.yml")
+	rightPath := filepath.Join(directory, "after.yml")
+	if err := os.WriteFile(leftPath, []byte("name: before\nentries: {}\n"), 0o600); err != nil {
+		fmt.Println(err)
+		return
+	}
+	if err := os.WriteFile(rightPath, []byte("name: after\nentries:\n  added: null\n"), 0o600); err != nil {
+		fmt.Println(err)
+		return
+	}
+	output, err := consumers.CompareFiles(leftPath, rightPath)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Print(output)
+	// Output:
+	// /entries/added: left=<absent> right="null\n"
+	// /name: left="before\n" right="after\n"
+}
+
+func ExampleCompareRolloutOverlay() {
+	const baseToken = "CONFIGKIT_DIFF_EXAMPLE_BASE_TOKEN"
+	const overlayToken = "CONFIGKIT_DIFF_EXAMPLE_OVERLAY_TOKEN"
+	defer preserveEnvironment(baseToken)()
+	defer preserveEnvironment(overlayToken)()
+	_ = os.Setenv(baseToken, "disposable-example-base-credential")
+	_ = os.Setenv(overlayToken, "disposable-example-overlay-credential")
+
+	directory, err := os.MkdirTemp("", "configkit-diff-overlay-")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	defer os.RemoveAll(directory)
+	basePath := filepath.Join(directory, "config.yml")
+	overlayPath := filepath.Join(directory, "overlays", "canary.yml")
+	if err := os.MkdirAll(filepath.Dir(overlayPath), 0o700); err != nil {
+		fmt.Println(err)
+		return
+	}
+	base := "service:\n  endpoint:\n    host: base.example\n    port: 8443\n  credential:\n    token: " + baseToken + "\n"
+	overlay := "service:\n  endpoint:\n    host: canary.example\n  credential:\n    token: " + overlayToken + "\n"
+	if err := os.WriteFile(basePath, []byte(base), 0o600); err != nil {
+		fmt.Println(err)
+		return
+	}
+	if err := os.WriteFile(overlayPath, []byte(overlay), 0o600); err != nil {
+		fmt.Println(err)
+		return
+	}
+	output, err := consumers.CompareRolloutOverlay(basePath, "canary")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Print(output)
+	// Output:
+	// /service/credential/token: left="'[REDACTED]'\n" right="'[REDACTED]'\n" hidden-change
+	// /service/endpoint/host: left="base.example\n" right="canary.example\n"
+	// /service/endpoint/url: left="https://base.example:8443\n" right="https://canary.example:8443\n"
+}
+
+func TestCompareFilesUsesCallerSelectedSourcesAndSafePresence(t *testing.T) {
+	directory := t.TempDir()
+	leftPath := filepath.Join(directory, "before.yml")
+	rightPath := filepath.Join(directory, "after.yml")
+	writeConfiguration(t, leftPath, "name: before\nentries: {}\n")
+	writeConfiguration(t, rightPath, "name: after\nentries:\n  added: null\n")
+
+	output, err := consumers.CompareFiles(leftPath, rightPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := "/entries/added: left=<absent> right=\"null\\n\"\n" +
+		"/name: left=\"before\\n\" right=\"after\\n\"\n"
+	if output != want {
+		t.Fatalf("comparison output = %q, want %q", output, want)
+	}
+	if again, err := consumers.CompareFiles(leftPath, rightPath); err != nil || again != output {
+		t.Fatalf("repeat output = %q, %v", again, err)
+	}
+}
+
+func TestCompareFilesReturnsEachLoadError(t *testing.T) {
+	directory := t.TempDir()
+	leftPath := filepath.Join(directory, "before.yml")
+	rightPath := filepath.Join(directory, "after.yml")
+	writeConfiguration(t, leftPath, "name: before\n")
+	writeConfiguration(t, rightPath, "unknown: invalid\n")
+
+	output, err := consumers.CompareFiles(leftPath, rightPath)
+	if err == nil || output != "" || !strings.Contains(err.Error(), "load right configuration") {
+		t.Fatalf("right load failure = %q, %v", output, err)
+	}
+	if _, err := consumers.CompareFiles(filepath.Join(directory, "missing.yml"), rightPath); err == nil || !strings.Contains(err.Error(), "load left configuration") {
+		t.Fatalf("left load failure = %v", err)
+	}
+}
+
+func TestCompareRolloutOverlayShowsResolvedSafeChangesAndRetainsSiblings(t *testing.T) {
+	t.Setenv("CONFIGKIT_DIFF_BASE_TOKEN", "disposable-base-credential")
+	t.Setenv("CONFIGKIT_DIFF_OVERLAY_TOKEN", "disposable-overlay-credential")
+	directory := t.TempDir()
+	basePath := filepath.Join(directory, "config.yml")
+	overlayPath := filepath.Join(directory, "overlays", "canary.yml")
+	if err := os.MkdirAll(filepath.Dir(overlayPath), 0o700); err != nil {
+		t.Fatal(err)
+	}
+	writeConfiguration(t, basePath, "service:\n  endpoint:\n    host: base.example\n    port: 8443\n  credential:\n    token: CONFIGKIT_DIFF_BASE_TOKEN\n")
+	writeConfiguration(t, overlayPath, "service:\n  endpoint:\n    host: canary.example\n  credential:\n    token: CONFIGKIT_DIFF_OVERLAY_TOKEN\n")
+
+	base, err := consumers.LoadRollout(basePath, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	withOverlay, err := consumers.LoadRollout(basePath, "canary")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if base.Config.Service.Endpoint.Port != 8443 || withOverlay.Config.Service.Endpoint.Port != 8443 {
+		t.Fatalf("lower-priority port was not retained: base=%#v overlay=%#v", base.Config.Service.Endpoint, withOverlay.Config.Service.Endpoint)
+	}
+	urlInfo, found := withOverlay.Metadata().Lookup(configkit.Keys("service", "endpoint", "url"))
+	if !found || urlInfo.Origin.Layer != configkit.LayerResolution || withOverlay.Config.Service.Endpoint.URL != "https://canary.example:8443" {
+		t.Fatalf("resolved endpoint = %#v, metadata=%#v, %v", withOverlay.Config.Service.Endpoint, urlInfo, found)
+	}
+
+	differences, err := configkit.Diff(base, withOverlay)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(differences) != 3 {
+		t.Fatalf("differences = %#v", differences)
+	}
+	wantPaths := []string{"/service/credential/token", "/service/endpoint/host", "/service/endpoint/url"}
+	for index, difference := range differences {
+		if got := difference.Path.String(); got != wantPaths[index] {
+			t.Errorf("path[%d] = %q, want %q", index, got, wantPaths[index])
+		}
+	}
+	secret := differences[0]
+	if !secret.Left.Redacted || !secret.Right.Redacted || !secret.HiddenChanged || secret.Left.YAML != "'[REDACTED]'\n" || secret.Right.YAML != "'[REDACTED]'\n" {
+		t.Fatalf("classified credential difference = %#v", secret)
+	}
+	if strings.Contains(consumers.FormatDifferences(differences), "disposable-") {
+		t.Fatal("formatted differences exposed credential contents")
+	}
+
+	output, err := consumers.CompareRolloutOverlay(basePath, "canary")
+	if err != nil || output != consumers.FormatDifferences(differences) {
+		t.Fatalf("formatted base/overlay comparison = %q, %v", output, err)
+	}
+}
+
+func TestFormatDifferencesUsesRecordMembershipForNoChange(t *testing.T) {
+	if got := consumers.FormatDifferences(nil); got != "No effective changes.\n" {
+		t.Fatalf("no-change output = %q", got)
+	}
+}
+
+func writeConfiguration(t *testing.T, filename, contents string) {
+	t.Helper()
+	if err := os.WriteFile(filename, []byte(contents), 0o600); err != nil {
+		t.Fatal(err)
+	}
+}

facade_diff_test.go

@@ -0,0 +1,327 @@
+package configkit_test
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+type facadeDiffConfig struct {
+	Value   string         `yaml:"value"`
+	Count   int            `yaml:"count"`
+	Items   []string       `yaml:"items"`
+	Dynamic map[string]any `yaml:"dynamic"`
+}
+
+type facadeDiffSecretConfig struct {
+	Secret configkit.Secret `yaml:"secret"`
+}
+
+func TestFacadeDiffKeepsPublicSequenceChangesWithHistoricalDescendants(t *testing.T) {
+	type configuration struct {
+		Items []any `yaml:"items"`
+	}
+	load := func(public string) *configkit.Result[configuration] {
+		t.Helper()
+		result, err := configkit.Load(configkit.Bytes("historical-sequence.yml", []byte("items: [{secret: disposable-canary}, "+public+"]\n")),
+			configkit.Options[configuration]{Definition: configkit.Definition[configuration]{
+				Secret: func(path configkit.Path) bool { return path.String() == "/items/0/secret" },
+				Resolve: func(current *configuration, resolution *configkit.Resolution) error {
+					current.Items[0] = "public scalar"
+					resolution.Record(configkit.Keys("items"), configkit.ChangeNormalization, "normalize first item")
+					return nil
+				},
+			}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return result
+	}
+	left, right := load("1"), load("2")
+	history, ok := left.Explain(configkit.Keys("items").Index(0).Key("secret"))
+	if !ok || history.Effective.Present || len(history.History) == 0 {
+		t.Fatalf("removed historical secret = %#v, known=%v", history, ok)
+	}
+	maskedHistory := false
+	for _, change := range history.History {
+		maskedHistory = maskedHistory || change.Before.Redacted || change.After.Redacted
+	}
+	if !maskedHistory {
+		t.Fatal("historical sensitivity was not retained")
+	}
+	differences, err := configkit.Diff(left, right)
+	if err != nil || len(differences) != 1 || differences[0].Path.String() != "/items" {
+		t.Fatalf("sequence difference = %#v, %v", differences, err)
+	}
+	difference := differences[0]
+	if !difference.Left.Present || !difference.Right.Present || difference.Left.Redacted || difference.Right.Redacted || difference.HiddenChanged {
+		t.Fatalf("public sequence change was concealed: %#v", difference)
+	}
+	if difference.Left.YAML != "- public scalar\n- 1\n" || difference.Right.YAML != "- public scalar\n- 2\n" {
+		t.Fatalf("public sequence snapshots = %#v", difference)
+	}
+}
+
+func TestFacadeDiffKeepsPublicScalarAcrossHistoricalAbsence(t *testing.T) {
+	type configuration struct {
+		Dynamic map[string]any `yaml:"dynamic"`
+	}
+	options := configkit.Options[configuration]{Definition: configkit.Definition[configuration]{
+		Secret: func(path configkit.Path) bool { return path.String() == "/dynamic/entry/token" },
+		Resolve: func(current *configuration, resolution *configkit.Resolution) error {
+			delete(current.Dynamic, "entry")
+			resolution.Record(configkit.Keys("dynamic", "entry"), configkit.ChangeNormalization, "remove entry")
+			return nil
+		},
+	}}
+	absent, err := configkit.Load(configkit.Bytes("removed-entry.yml", []byte("dynamic: {entry: {token: disposable-canary}}\n")), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	options.Definition.Resolve = nil
+	present, err := configkit.Load(configkit.Bytes("public-entry.yml", []byte("dynamic: {entry: public}\n")), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, test := range []struct {
+		name        string
+		left, right *configkit.Result[configuration]
+		leftPresent bool
+	}{
+		{name: "addition", left: absent, right: present},
+		{name: "removal", left: present, right: absent, leftPresent: true},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			differences, err := configkit.Diff(test.left, test.right)
+			if err != nil || len(differences) != 1 || differences[0].Path.String() != "/dynamic/entry" {
+				t.Fatalf("entry difference = %#v, %v", differences, err)
+			}
+			difference := differences[0]
+			if difference.Left.Present != test.leftPresent || difference.Right.Present == test.leftPresent ||
+				difference.Left.Redacted || difference.Right.Redacted || difference.HiddenChanged {
+				t.Fatalf("public presence change was concealed: %#v", difference)
+			}
+			wantLeft, wantRight := "", "public\n"
+			if test.leftPresent {
+				wantLeft, wantRight = wantRight, wantLeft
+			}
+			if difference.Left.YAML != wantLeft || difference.Right.YAML != wantRight {
+				t.Fatalf("entry snapshots = %#v", difference)
+			}
+		})
+	}
+}
+
+func TestFacadeDiffReturnsDetachedCanonicalRecords(t *testing.T) {
+	left, err := configkit.Load[facadeDiffConfig](configkit.Bytes("left.yml", []byte("value: before\ncount: 0\nitems: [one, two]\ndynamic: {}\n")))
+	if err != nil {
+		t.Fatalf("load left: %v", err)
+	}
+	right, err := configkit.Load[facadeDiffConfig](configkit.Bytes("right.yml", []byte("value: after\ncount: 0\nitems: [one, three]\ndynamic:\n  added: null\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	differences, err := configkit.Diff(left, right)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantPaths := []string{"/dynamic/added", "/items", "/value"}
+	if len(differences) != len(wantPaths) {
+		t.Fatalf("differences = %#v", differences)
+	}
+	for index, difference := range differences {
+		if got := difference.Path.String(); got != wantPaths[index] {
+			t.Errorf("path[%d] = %q, want %q", index, got, wantPaths[index])
+		}
+	}
+	if differences[0].Left.Present || !differences[0].Right.Present || differences[0].Right.YAML != "null\n" {
+		t.Errorf("null/absence snapshots = %#v / %#v", differences[0].Left, differences[0].Right)
+	}
+	if differences[1].Left.YAML != "- one\n- two\n" || differences[1].Right.YAML != "- one\n- three\n" {
+		t.Errorf("sequence snapshots = %#v / %#v", differences[1].Left, differences[1].Right)
+	}
+
+	left.Config.Value = "caller mutation"
+	left.Config.Items[0] = "caller mutation"
+	right.Config.Dynamic["added"] = "caller mutation"
+	differences[2].Left.YAML = "record mutation"
+	differences[2].Path = configkit.Keys("rewritten")
+
+	again, err := configkit.Diff(left, right)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if again[2].Path.String() != "/value" || again[2].Left.YAML != "before\n" || again[1].Left.YAML != "- one\n- two\n" {
+		t.Fatalf("repeat diff changed = %#v", again)
+	}
+	explanation, ok := left.Explain(configkit.Keys("value"))
+	if !ok || explanation.Effective.YAML != "before\n" {
+		t.Fatalf("frozen explanation = %#v, %v", explanation, ok)
+	}
+}
+
+func TestFacadeDiffRejectsUnavailableResults(t *testing.T) {
+	type config struct {
+		Value string `yaml:"value"`
+	}
+	loaded, err := configkit.Load[config](configkit.Bytes("valid.yml", []byte("value: valid\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var nilResult *configkit.Result[config]
+	zeroResult := &configkit.Result[config]{Config: config{Value: "must not be inspected"}}
+	for name, left := range map[string]*configkit.Result[config]{"nil": nilResult, "zero": zeroResult} {
+		t.Run(name, func(t *testing.T) {
+			if records, err := configkit.Diff(left, loaded); err == nil || records != nil {
+				t.Fatalf("Diff = %#v, %v; want nil records and error", records, err)
+			}
+		})
+	}
+	if records, err := configkit.Diff(loaded, nilResult); err == nil || records != nil {
+		t.Fatalf("right nil Diff = %#v, %v", records, err)
+	}
+}
+
+func TestFacadeDiffIgnoresSourceAndResolutionHistory(t *testing.T) {
+	type config struct {
+		Count int `yaml:"count"`
+	}
+	defaults := configkit.Options[config]{Definition: configkit.Definition[config]{
+		Defaults: func() config { return config{Count: 7} },
+	}}
+	defaulted, err := configkit.Load[config](configkit.NoSource(), defaults)
+	if err != nil {
+		t.Fatal(err)
+	}
+	explicit, err := configkit.Load[config](configkit.Bytes("explicit.yml", []byte("count: 7\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if differences, err := configkit.Diff(defaulted, explicit); err != nil || len(differences) != 0 {
+		t.Fatalf("default/source difference = %#v, %v", differences, err)
+	}
+
+	zeroDefault, err := configkit.Load[config](configkit.NoSource(), configkit.Options[config]{Definition: configkit.Definition[config]{Defaults: func() config { return config{} }}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	explicitZero, err := configkit.Load[config](configkit.Bytes("explicit-zero.yml", []byte("count: 0\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if differences, err := configkit.Diff(zeroDefault, explicitZero); err != nil || len(differences) != 0 {
+		t.Fatalf("explicit/defaulted zero difference = %#v, %v", differences, err)
+	}
+
+	resolve := func(value string) configkit.Options[config] {
+		return configkit.Options[config]{Definition: configkit.Definition[config]{Resolve: func(current *config, resolution *configkit.Resolution) error {
+			current.Count = len(value) + 8
+			resolution.Record(configkit.Keys("count"), configkit.ChangeNormalization, "set effective count")
+			return nil
+		}}}
+	}
+	resolvedA, err := configkit.Load[config](configkit.Bytes("a.yml", []byte("{}\n")), resolve("a"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	resolvedB, err := configkit.Load[config](configkit.Bytes("b.yml", []byte("{}\n")), resolve("b"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if differences, err := configkit.Diff(resolvedA, resolvedB); err != nil || len(differences) != 0 {
+		t.Fatalf("equal resolved values = %#v, %v", differences, err)
+	}
+}
+
+func TestFacadeDiffUsesFrozenFilesAndRunsCallbacksOnlyDuringLoad(t *testing.T) {
+	type config struct {
+		Value string `yaml:"value"`
+	}
+	calls := 0
+	options := configkit.Options[config]{Definition: configkit.Definition[config]{Defaults: func() config {
+		calls++
+		return config{}
+	}}}
+	dir := t.TempDir()
+	paths := []string{filepath.Join(dir, "left.yml"), filepath.Join(dir, "right.yml")}
+	for index, contents := range []string{"value: left\n", "value: right\n"} {
+		if err := os.WriteFile(paths[index], []byte(contents), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	left, err := configkit.Load[config](configkit.File(paths[0]), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	right, err := configkit.Load[config](configkit.File(paths[1]), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if calls != 2 {
+		t.Fatalf("defaults calls after loads = %d", calls)
+	}
+	for _, path := range paths {
+		if err := os.Remove(path); err != nil {
+			t.Fatal(err)
+		}
+	}
+	differences, err := configkit.Diff(left, right)
+	if err != nil || len(differences) != 1 || differences[0].Path.String() != "/value" {
+		t.Fatalf("Diff after removing files = %#v, %v", differences, err)
+	}
+	if calls != 2 {
+		t.Fatalf("defaults reran during Diff: %d calls", calls)
+	}
+}
+
+func TestFacadeDiffCombinesSecretSensitivityAndLoadErrors(t *testing.T) {
+	t.Setenv("FACADE_DIFF_SECRET", "credential-one")
+	secretOptions := configkit.Options[facadeDiffSecretConfig]{Definition: configkit.Definition[facadeDiffSecretConfig]{Secret: func(path configkit.Path) bool {
+		return path.String() == "/secret"
+	}}}
+	left, err := configkit.Load[facadeDiffSecretConfig](configkit.Bytes("left.yml", []byte("secret: FACADE_DIFF_SECRET\n")), secretOptions)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("FACADE_DIFF_SECRET", "credential-two")
+	right, err := configkit.Load[facadeDiffSecretConfig](configkit.Bytes("right.yml", []byte("secret: FACADE_DIFF_SECRET\n")), secretOptions)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if differences, err := configkit.Diff(left, right); err != nil || len(differences) != 0 {
+		t.Fatalf("credential rotation = %#v, %v", differences, err)
+	}
+	t.Setenv("OTHER_FACADE_DIFF_SECRET", "other-credential")
+	otherReference, err := configkit.Load[facadeDiffSecretConfig](configkit.Bytes("other.yml", []byte("secret: OTHER_FACADE_DIFF_SECRET\n")), secretOptions)
+	if err != nil {
+		t.Fatal(err)
+	}
+	differences, err := configkit.Diff(left, otherReference)
+	if err != nil || len(differences) != 1 || !differences[0].HiddenChanged || !differences[0].Left.Redacted || !differences[0].Right.Redacted {
+		t.Fatalf("reference change = %#v, %v", differences, err)
+	}
+	if strings.Contains(differences[0].Left.YAML+differences[0].Right.YAML, "credential") {
+		t.Fatalf("credential leaked: %#v", differences)
+	}
+
+	invalidLeft, leftErr := configkit.Load[facadeDiffSecretConfig](configkit.Bytes("invalid-left.yml", []byte("unknown: true\n")))
+	if invalidLeft != nil || leftErr == nil {
+		t.Fatalf("invalid left load = %#v, %v", invalidLeft, leftErr)
+	}
+	var loadError *configkit.LoadError
+	if !errors.As(leftErr, &loadError) {
+		t.Fatalf("left load error = %T, want *configkit.LoadError", leftErr)
+	}
+	invalidRight, rightErr := configkit.Load[facadeDiffSecretConfig](configkit.Bytes("invalid-right.yml", []byte("unknown: true\n")))
+	if invalidRight != nil || rightErr == nil {
+		t.Fatalf("invalid right load = %#v, %v", invalidRight, rightErr)
+	}
+	if !errors.As(rightErr, &loadError) {
+		t.Fatalf("right load error = %T, want *configkit.LoadError", rightErr)
+	}
+}

go.mod

@@ -1,5 +1,13 @@
 module gitea.maximumdirect.net/eric/ConfigKit
 
-go 1.25.0
+go 1.26.0
 
 require go.yaml.in/yaml/v4 v4.0.0-rc.6
+
+require (
+	gitea.maximumdirect.net/eric/ReleaseKit v0.4.1 // indirect
+	github.com/yuin/goldmark/v2 v2.1.6 // indirect
+	golang.org/x/mod v0.40.0 // indirect
+)
+
+tool gitea.maximumdirect.net/eric/ReleaseKit/cmd/releasekit

go.sum

@@ -1,2 +1,8 @@
+gitea.maximumdirect.net/eric/ReleaseKit v0.4.1 h1:Qn+mdebYOzCVCEXgCbuGSO/WHmJtItwaQ8e3XwY3qtI=
+gitea.maximumdirect.net/eric/ReleaseKit v0.4.1/go.mod h1:LVodqNQ3OIKv9NBq+fFeyMByd1lHY25YOmmpah/NaNI=
+github.com/yuin/goldmark/v2 v2.1.6 h1:igy0q9JcqovoFXFx/XjtU8sHVhcUHavPj2sA3EoKJUE=
+github.com/yuin/goldmark/v2 v2.1.6/go.mod h1:G6M4/qOFtfn01/o14BU1UR2Lo5N3S9Qo7xCuz/sHjGQ=
 go.yaml.in/yaml/v4 v4.0.0-rc.6 h1:1h7H1ohdUh93/FyE4YaDa1Zh64K6VVbjF4K6WUxMtH4=
 go.yaml.in/yaml/v4 v4.0.0-rc.6/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=
+golang.org/x/mod v0.40.0 h1:hUv+3cXcdRHz08UmSiOob7sadHig73uo5bkXxQ/tvUs=
+golang.org/x/mod v0.40.0/go.mod h1:0/weTWkPWGBikyTWAX3dkjVztMmBA5hM0DH6BElSupE=

internal/engine/diagnostic.go

@@ -85,15 +85,28 @@ func canonicalDiagnostics(diagnostics []Diagnostic) []Diagnostic {
 	for i := range canonical {
 		slices.SortFunc(canonical[i].Related, compareLocation)
 	}
-	slices.SortFunc(canonical, compareDiagnostic)
+	type orderedDiagnostic struct {
+		diagnostic Diagnostic
+		pointer    string
+	}
+	ordered := make([]orderedDiagnostic, len(canonical))
+	for i, diagnostic := range canonical {
+		ordered[i] = orderedDiagnostic{diagnostic: diagnostic, pointer: diagnostic.Path.String()}
+	}
+	slices.SortFunc(ordered, func(left, right orderedDiagnostic) int {
+		return compareDiagnosticWithPaths(left.diagnostic, right.diagnostic, left.pointer, right.pointer)
+	})
+	for i, item := range ordered {
+		canonical[i] = item.diagnostic
+	}
 	return canonical
 }
 
-func compareDiagnostic(left, right Diagnostic) int {
+func compareDiagnosticWithPaths(left, right Diagnostic, leftPath, rightPath string) int {
 	if order := compareOptionalLocation(left.Primary, right.Primary); order != 0 {
 		return order
 	}
-	if order := cmp.Compare(left.Path.String(), right.Path.String()); order != 0 {
+	if order := cmp.Compare(leftPath, rightPath); order != 0 {
 		return order
 	}
 	if order := cmp.Compare(left.Code, right.Code); order != 0 {

internal/engine/diagnostic_test.go

@@ -90,6 +90,26 @@ func TestDiagnosticsAreCanonicalAndDetached(t *testing.T) {
 	}
 }
 
+func TestCanonicalDiagnosticsSortEscapedPaths(t *testing.T) {
+	primary := &Location{SourceID: "source-1", Line: 1, Column: 1}
+	diagnostics := []Diagnostic{
+		{Code: "same", Severity: SeverityError, Path: Keys("a/b"), Message: "same", Primary: primary},
+		{Code: "same", Severity: SeverityError, Path: Keys("a~b"), Message: "same", Primary: primary},
+		{Code: "z", Severity: SeverityError, Path: Keys("same"), Message: "same", Primary: primary},
+		{Code: "a", Severity: SeverityError, Path: Keys("same"), Message: "same", Primary: primary},
+	}
+	canonical := canonicalDiagnostics(diagnostics)
+	want := []string{"/a~0b", "/a~1b", "/same", "/same"}
+	for i, diagnostic := range canonical {
+		if got := diagnostic.Path.String(); got != want[i] {
+			t.Fatalf("diagnostic[%d] path = %q, want %q", i, got, want[i])
+		}
+	}
+	if canonical[2].Code != "a" || canonical[3].Code != "z" {
+		t.Fatalf("same-path code order = %q, %q", canonical[2].Code, canonical[3].Code)
+	}
+}
+
 func TestWriteDiagnosticsEscapesControls(t *testing.T) {
 	t.Parallel()
 

internal/engine/diff.go

@@ -0,0 +1,98 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"io"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+	yamladapter "gitea.maximumdirect.net/eric/ConfigKit/internal/yaml"
+)
+
+var errDiffInspectionUnavailable = errors.New("configkit: diff inspection unavailable")
+var errDiffSnapshotUnavailable = errors.New("configkit: diff snapshot unavailable")
+
+// Difference describes one canonical changed region with safe snapshots.
+type Difference struct {
+	Path          Path
+	Left          ValueSnapshot
+	Right         ValueSnapshot
+	HiddenChanged bool
+}
+
+type diffRegion struct {
+	path  Path
+	left  *document.Node
+	right *document.Node
+}
+
+func prepareDiffRegions(left, right *Inspection) ([]diffRegion, error) {
+	if left == nil || left.final == nil || right == nil || right.final == nil {
+		return nil, errDiffInspectionUnavailable
+	}
+
+	deltas := compareConfigurationValues(left.final, right.final)
+	regions := make([]diffRegion, 0, len(deltas))
+	for _, delta := range deltas {
+		leftNode, leftPresent := documentAtPathWithLookup(left.final, delta.path, left.immutableLookup)
+		if !leftPresent {
+			leftNode = nil
+		}
+		rightNode, rightPresent := documentAtPathWithLookup(right.final, delta.path, right.immutableLookup)
+		if !rightPresent {
+			rightNode = nil
+		}
+		regions = append(regions, diffRegion{path: delta.path, left: leftNode, right: rightNode})
+	}
+	return regions, nil
+}
+
+// Diff compares the final frozen values retained by two successful inspections.
+// Values are serialized only after applying the combined sensitivity of both loads.
+func Diff(left, right *Inspection) ([]Difference, error) {
+	regions, err := prepareDiffRegions(left, right)
+	if err != nil {
+		return nil, err
+	}
+	sensitivity := newDiffSensitivity(left.secrets, right.secrets)
+	differences := make([]Difference, 0, len(regions))
+	for _, region := range regions {
+		paired, supported := preparePairedDiffSnapshot(region.left, region.right, region.path, sensitivity)
+		if !supported {
+			return nil, errDiffSnapshotUnavailable
+		}
+		leftSnapshot, err := serializeDiffSnapshot(paired.left, paired.leftRedacted)
+		if err != nil {
+			return nil, errDiffSnapshotUnavailable
+		}
+		rightSnapshot, err := serializeDiffSnapshot(paired.right, paired.rightRedacted)
+		if err != nil {
+			return nil, errDiffSnapshotUnavailable
+		}
+		differences = append(differences, Difference{
+			Path:          region.path,
+			Left:          leftSnapshot,
+			Right:         rightSnapshot,
+			HiddenChanged: paired.hiddenChanged,
+		})
+	}
+	return differences, nil
+}
+
+func serializeDiffSnapshot(node *document.Node, redacted bool) (ValueSnapshot, error) {
+	if node == nil {
+		return ValueSnapshot{}, nil
+	}
+	var output bytes.Buffer
+	if err := writeDiffDocument(&output, node); err != nil {
+		return ValueSnapshot{}, errDiffSnapshotUnavailable
+	}
+	return ValueSnapshot{Present: true, Redacted: redacted, YAML: output.String()}, nil
+}
+
+func writeDiffDocument(output io.Writer, node *document.Node) error {
+	if err := yamladapter.Write(output, node); err != nil {
+		return errDiffSnapshotUnavailable
+	}
+	return nil
+}

internal/engine/diff_hidden_test.go

@@ -0,0 +1,130 @@
+package engine
+
+import (
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestPreparePairedDiffSnapshotReportsWhollyMaskedChanges(t *testing.T) {
+	left := &document.Node{Kind: document.String, Text: "private-before"}
+	right := &document.Node{Kind: document.String, Text: "private-after"}
+	paired, supported := preparePairedDiffSnapshot(
+		left, right, Keys("credential"), newDiffSensitivity(nil, map[string]bool{"/credential": true}),
+	)
+	if !supported || !paired.hiddenChanged || !paired.leftRedacted || !paired.rightRedacted {
+		t.Fatalf("masked change = %#v, supported=%v", paired, supported)
+	}
+	assertDiffStringNode(t, paired.left, "[REDACTED]")
+	assertDiffStringNode(t, paired.right, "[REDACTED]")
+}
+
+func TestPreparePairedDiffSnapshotDetectsRawChangesBehindIdenticalMarkers(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "token: old-canary\n")
+	right := parseCompositionDocument(t, "right", "token: new-canary\n")
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "token"), mappingValue(t, right, "token"), Keys("token"),
+		newDiffSensitivity(map[string]bool{"/token": true}, nil),
+	)
+	if !supported || !paired.hiddenChanged || paired.left.Text != paired.right.Text {
+		t.Fatalf("identically rendered masked values lost raw change: %#v, supported=%v", paired, supported)
+	}
+}
+
+func TestPreparePairedDiffSnapshotCombinesPublicAndHiddenChanges(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "public: before\ntoken: old\n")
+	right := parseCompositionDocument(t, "right", "public: after\ntoken: new\n")
+	paired, supported := preparePairedDiffSnapshot(
+		left, right, Path{}, newDiffSensitivity(nil, map[string]bool{"/token": true}),
+	)
+	if !supported || !paired.hiddenChanged {
+		t.Fatalf("mixed public and hidden change = %#v, supported=%v", paired, supported)
+	}
+	assertDiffStringNode(t, mappingValue(t, paired.left, "public"), "before")
+	assertDiffStringNode(t, mappingValue(t, paired.right, "public"), "after")
+	assertDiffStringNode(t, mappingValue(t, paired.left, "token"), "[REDACTED]")
+	assertDiffStringNode(t, mappingValue(t, paired.right, "token"), "[REDACTED]")
+}
+
+func TestPreparePairedDiffSnapshotDoesNotFlagUnchangedMaskedValues(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "public: before\ntoken: unchanged\n")
+	right := parseCompositionDocument(t, "right", "public: after\ntoken: unchanged\n")
+	regions, err := prepareDiffRegions(diffTestInspection(left), diffTestInspection(right))
+	if err != nil || len(regions) != 1 || regions[0].path.String() != "/public" {
+		t.Fatalf("changed regions = %#v, err = %v; want only /public", regions, err)
+	}
+	paired, supported := preparePairedDiffSnapshot(
+		left, right, Path{}, newDiffSensitivity(map[string]bool{"/token": true}, nil),
+	)
+	if !supported || !paired.leftRedacted || !paired.rightRedacted || paired.hiddenChanged {
+		t.Fatalf("unchanged masked values affected hidden-change state: %#v, supported=%v", paired, supported)
+	}
+
+	leftSequence := parseCompositionDocument(t, "left-sequence", "items: [unchanged, before]\n")
+	rightSequence := parseCompositionDocument(t, "right-sequence", "items: [unchanged, after]\n")
+	sequence, supported := preparePairedDiffSnapshot(
+		mappingValue(t, leftSequence, "items"), mappingValue(t, rightSequence, "items"), Keys("items"),
+		newDiffSensitivity(nil, map[string]bool{"/items/0": true}),
+	)
+	if !supported || !sequence.leftRedacted || !sequence.rightRedacted || sequence.hiddenChanged {
+		t.Fatalf("unchanged masked sequence member affected hidden-change state: %#v, supported=%v", sequence, supported)
+	}
+}
+
+func TestPreparePairedDiffSnapshotReportsMaskedAdditionAndRemoval(t *testing.T) {
+	value := &document.Node{Kind: document.String, Text: "private"}
+	tests := []struct {
+		name        string
+		left, right *document.Node
+		leftHidden  bool
+		rightHidden bool
+	}{
+		{name: "addition", right: value, rightHidden: true},
+		{name: "removal", left: value, leftHidden: true},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			paired, supported := preparePairedDiffSnapshot(
+				test.left, test.right, Keys("token"), newDiffSensitivity(nil, map[string]bool{"/token": true}),
+			)
+			if !supported || !paired.hiddenChanged || paired.leftRedacted != test.leftHidden || paired.rightRedacted != test.rightHidden {
+				t.Fatalf("masked presence change = %#v, supported=%v", paired, supported)
+			}
+			if test.left == nil && paired.left != nil || test.right == nil && paired.right != nil {
+				t.Fatalf("absence became a value: %#v", paired)
+			}
+		})
+	}
+}
+
+func TestPreparePairedDiffSnapshotReportsHiddenSequenceLengthChange(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "items: [public]\n")
+	right := parseCompositionDocument(t, "right", "items: [public, private]\n")
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "items"), mappingValue(t, right, "items"), Keys("items"),
+		newDiffSensitivity(nil, map[string]bool{"/items/1": true}),
+	)
+	if !supported || !paired.hiddenChanged || paired.leftRedacted || !paired.rightRedacted {
+		t.Fatalf("masked sequence length change = %#v, supported=%v", paired, supported)
+	}
+	if len(paired.left.Sequence) != 1 || len(paired.right.Sequence) != 2 {
+		t.Fatalf("safe sequence lengths = %d, %d; want 1, 2", len(paired.left.Sequence), len(paired.right.Sequence))
+	}
+	assertDiffStringNode(t, paired.right.Sequence[1], "[REDACTED]")
+}
+
+func TestPreparePairedDiffSnapshotClassificationAloneDoesNotCreateHiddenChange(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "token: same\n")
+	right := parseCompositionDocument(t, "right", "token: same\n")
+	regions, err := prepareDiffRegions(diffTestInspection(left), diffTestInspection(right))
+	if err != nil || len(regions) != 0 {
+		t.Fatalf("classification-independent changed regions = %#v, err = %v", regions, err)
+	}
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "token"), mappingValue(t, right, "token"), Keys("token"),
+		newDiffSensitivity(map[string]bool{"/token": true}, nil),
+	)
+	if !supported || !paired.leftRedacted || !paired.rightRedacted || paired.hiddenChanged {
+		t.Fatalf("classification alone reported hidden change: %#v, supported=%v", paired, supported)
+	}
+}

internal/engine/diff_operation_test.go

@@ -0,0 +1,282 @@
+package engine
+
+import (
+	"bytes"
+	"errors"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type diffIntegrationConfig struct {
+	Defaulted  string         `yaml:"defaulted"`
+	Dynamic    map[string]any `yaml:"dynamic"`
+	Credential Secret         `yaml:"credential" configkit:"secret"`
+	Derived    string         `yaml:"derived"`
+}
+
+type diffOptionalSecretConfig struct {
+	Optional *Secret `yaml:"optional" configkit:"secret"`
+}
+
+func TestDiffUsesFinalValuesAndDependencyDerivedSensitivity(t *testing.T) {
+	var resolveCalls int
+	options := Options[diffIntegrationConfig]{Definition: Definition[diffIntegrationConfig]{
+		Defaults: func() diffIntegrationConfig {
+			return diffIntegrationConfig{Defaulted: "from-default", Dynamic: map[string]any{"defaulted": "retained"}}
+		},
+		Resolve: func(configuration *diffIntegrationConfig, resolution *Resolution) error {
+			resolveCalls++
+			configuration.Derived = configuration.Dynamic["visible"].(string)
+			resolution.Record(Keys("derived"), ChangeNormalization, "derive from effective values", Keys("credential"))
+			return nil
+		},
+	}}
+	input := func(value string) Source {
+		return Bytes("effective.yml", []byte("dynamic: {visible: "+value+"}\ncredential: DIFF_ENGINE_SECRET\n"))
+	}
+	t.Setenv("DIFF_ENGINE_SECRET", "credential-left-canary")
+	left, err := testLoad(input("before"), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("DIFF_ENGINE_SECRET", "credential-right-canary")
+	right, err := testLoad(input("after"), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if left.Config.Defaulted != "from-default" || right.Config.Defaulted != "from-default" {
+		t.Fatalf("defaulted values = %q, %q", left.Config.Defaulted, right.Config.Defaulted)
+	}
+	if !left.Inspection.secrets["/credential"] || !left.Inspection.secrets["/derived"] ||
+		!right.Inspection.secrets["/credential"] || !right.Inspection.secrets["/derived"] {
+		t.Fatalf("typed or dependency-derived sensitivity was not retained: left=%#v right=%#v", left.Inspection.secrets, right.Inspection.secrets)
+	}
+	if node, present := documentAtPathWithLookup(left.Inspection.final, Keys("derived"), left.Inspection.immutableLookup); !present || node.Text != "before" {
+		t.Fatalf("left frozen derived value = %#v, present=%v", node, present)
+	}
+
+	differences, err := Diff(left.Inspection, right.Inspection)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(differences) != 2 || differences[0].Path.String() != "/derived" || differences[1].Path.String() != "/dynamic/visible" {
+		t.Fatalf("differences = %#v", differences)
+	}
+	if !differences[0].Left.Redacted || !differences[0].Right.Redacted || !differences[0].HiddenChanged ||
+		differences[0].Left.YAML != "'[REDACTED]'\n" || differences[0].Right.YAML != "'[REDACTED]'\n" {
+		t.Fatalf("dependency-derived difference = %#v", differences[0])
+	}
+	if differences[1].Left.Redacted || differences[1].Right.Redacted || differences[1].HiddenChanged ||
+		differences[1].Left.YAML != "before\n" || differences[1].Right.YAML != "after\n" {
+		t.Fatalf("public dynamic difference = %#v", differences[1])
+	}
+	for _, value := range differences {
+		if strings.Contains(value.Left.YAML+value.Right.YAML, "credential-") {
+			t.Fatal("diff snapshot exposed a resolved credential")
+		}
+	}
+
+	var effective bytes.Buffer
+	if err := left.Inspection.WriteEffective(&effective); err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(effective.String(), "credential-left-canary") {
+		t.Fatal("standalone effective rendering exposed a credential after diff")
+	}
+	explanation, ok := left.Inspection.Explain(Keys("derived"))
+	if !ok || !explanation.Effective.Redacted || explanation.Effective.YAML != "'[REDACTED]'\n" {
+		t.Fatalf("explanation changed after diff: %#v, ok=%v", explanation, ok)
+	}
+	if _, ok := left.Inspection.Metadata().Lookup(Keys("dynamic", "visible")); !ok {
+		t.Fatal("metadata lookup failed after diff")
+	}
+	if resolveCalls != 2 {
+		t.Fatalf("resolution callbacks ran during diff: %d calls", resolveCalls)
+	}
+
+	// Returned records can be modified without affecting a later comparison.
+	differences[0].Path.segments[0].key = "changed-by-caller"
+	differences[0].Left.YAML = "changed-by-caller"
+	t.Setenv("DIFF_ENGINE_SECRET", "credential-after-load-canary")
+	repeated, err := Diff(left.Inspection, right.Inspection)
+	if err != nil || len(repeated) != 2 || repeated[0].Path.String() != "/derived" || repeated[0].Left.YAML != "'[REDACTED]'\n" {
+		t.Fatalf("repeated diff = %#v, err = %v", repeated, err)
+	}
+	if resolveCalls != 2 {
+		t.Fatalf("repeated diff reran resolution: %d calls", resolveCalls)
+	}
+
+	independent, err := testLoad(input("before"), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resolveCalls != 3 {
+		t.Fatalf("independent load did not retain normal resolution behavior: %d calls", resolveCalls)
+	}
+	if _, err := Diff(left.Inspection, independent.Inspection); err != nil {
+		t.Fatalf("independent load comparison = %v", err)
+	}
+}
+
+func TestDiffUsesReferenceNamesAndFrozenSecretState(t *testing.T) {
+	loadReference := func(name string) *testResult[diffOptionalSecretConfig] {
+		t.Helper()
+		result, err := testLoad[diffOptionalSecretConfig](Bytes("secret-reference.yml", []byte("optional: "+name+"\n")))
+		if err != nil {
+			t.Fatal(err)
+		}
+		return result
+	}
+	t.Setenv("DIFF_ROTATING_SECRET", "first-credential-canary")
+	left := loadReference("DIFF_ROTATING_SECRET")
+	t.Setenv("DIFF_ROTATING_SECRET", "second-credential-canary")
+	right := loadReference("DIFF_ROTATING_SECRET")
+	t.Setenv("DIFF_ROTATING_SECRET", "changed-after-load-canary")
+	differences, err := Diff(left.Inspection, right.Inspection)
+	if err != nil || len(differences) != 0 {
+		t.Fatalf("credential rotation behind one reference = %#v, err = %v", differences, err)
+	}
+	if node, present := documentAtPathWithLookup(left.Inspection.final, Keys("optional"), left.Inspection.immutableLookup); !present || node.Text != "DIFF_ROTATING_SECRET" {
+		t.Fatalf("frozen reference = %#v, present=%v", node, present)
+	}
+	if node, present := documentAtPathWithLookup(right.Inspection.final, Keys("optional"), right.Inspection.immutableLookup); !present || node.Text != "DIFF_ROTATING_SECRET" {
+		t.Fatalf("right frozen reference = %#v, present=%v", node, present)
+	}
+
+	t.Setenv("DIFF_OTHER_SECRET", "other-credential-canary")
+	other := loadReference("DIFF_OTHER_SECRET")
+	differences, err = Diff(left.Inspection, other.Inspection)
+	if err != nil || len(differences) != 1 || differences[0].Path.String() != "/optional" {
+		t.Fatalf("reference-name change = %#v, err = %v", differences, err)
+	}
+	if !differences[0].Left.Present || !differences[0].Right.Present || !differences[0].Left.Redacted ||
+		!differences[0].Right.Redacted || !differences[0].HiddenChanged ||
+		differences[0].Left.YAML != "'[REDACTED]'\n" || differences[0].Right.YAML != "'[REDACTED]'\n" {
+		t.Fatalf("classified reference-name diff = %#v", differences[0])
+	}
+
+	absent, err := testLoad[diffOptionalSecretConfig](Bytes("absent-secret.yml", []byte("{}\n")))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if absent.Config.Optional != nil {
+		t.Fatalf("missing optional reference decoded as %#v", absent.Config.Optional)
+	}
+	if node, present := documentAtPathWithLookup(absent.Inspection.final, Keys("optional"), absent.Inspection.immutableLookup); !present || node.Kind != document.Null {
+		t.Fatalf("optional nil projection = %#v, present=%v", node, present)
+	}
+	differences, err = Diff(absent.Inspection, left.Inspection)
+	if err != nil || len(differences) != 1 || differences[0].Path.String() != "/optional" {
+		t.Fatalf("optional absence diff = %#v, err = %v", differences, err)
+	}
+	if !differences[0].Left.Present || !differences[0].Left.Redacted ||
+		!differences[0].Right.Present || !differences[0].Right.Redacted || !differences[0].HiddenChanged {
+		t.Fatalf("optional reference change snapshots = %#v", differences[0])
+	}
+	for _, value := range differences {
+		if strings.Contains(value.Left.YAML+value.Right.YAML, "credential-canary") {
+			t.Fatal("reference diff exposed a resolved credential")
+		}
+	}
+}
+
+func TestDiffProtectsHistoricalSensitiveRemovalAndReplacement(t *testing.T) {
+	type configuration struct {
+		Dynamic map[string]any `yaml:"dynamic"`
+	}
+	secretPath := Keys("dynamic", "token")
+	secretSelector := func(path Path) bool { return path.String() == secretPath.String() }
+	load := func(input string, resolve func(*configuration, *Resolution) error) *testResult[configuration] {
+		t.Helper()
+		result, err := testLoad(Bytes("historical-secret.yml", []byte(input)), Options[configuration]{Definition: Definition[configuration]{
+			Secret:  secretSelector,
+			Resolve: resolve,
+		}})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return result
+	}
+
+	t.Run("removed historical value", func(t *testing.T) {
+		left := load("dynamic: {token: removed-canary}\n", func(configuration *configuration, resolution *Resolution) error {
+			delete(configuration.Dynamic, "token")
+			resolution.Record(secretPath, ChangeNormalization, "remove token")
+			return nil
+		})
+		right := load("dynamic: {token: current-canary}\n", nil)
+		if !left.Inspection.secrets[secretPath.String()] {
+			t.Fatal("removed historical selector was not retained")
+		}
+		if _, present := documentAtPathWithLookup(left.Inspection.final, secretPath, left.Inspection.immutableLookup); present {
+			t.Fatal("removed token remains in the effective left tree")
+		}
+		differences, err := Diff(left.Inspection, right.Inspection)
+		if err != nil || len(differences) != 1 || differences[0].Path.String() != secretPath.String() {
+			t.Fatalf("historical removal diff = %#v, err = %v", differences, err)
+		}
+		if differences[0].Left.Present || !differences[0].Right.Present || !differences[0].Right.Redacted || !differences[0].HiddenChanged {
+			t.Fatalf("historical removal snapshots = %#v", differences[0])
+		}
+		if strings.Contains(differences[0].Left.YAML+differences[0].Right.YAML, "canary") {
+			t.Fatal("historical removal diff exposed a sensitive value")
+		}
+	})
+
+	t.Run("replaced historical value", func(t *testing.T) {
+		left := load("dynamic: {token: original-canary}\n", func(configuration *configuration, resolution *Resolution) error {
+			configuration.Dynamic["token"] = "replacement-canary"
+			resolution.Record(secretPath, ChangeNormalization, "replace token")
+			return nil
+		})
+		right := load("dynamic: {token: other-canary}\n", nil)
+		if !left.Inspection.secrets[secretPath.String()] {
+			t.Fatal("replaced historical selector was not retained")
+		}
+		differences, err := Diff(left.Inspection, right.Inspection)
+		if err != nil || len(differences) != 1 || differences[0].Path.String() != secretPath.String() {
+			t.Fatalf("historical replacement diff = %#v, err = %v", differences, err)
+		}
+		if !differences[0].Left.Present || !differences[0].Right.Present || !differences[0].Left.Redacted ||
+			!differences[0].Right.Redacted || !differences[0].HiddenChanged {
+			t.Fatalf("historical replacement snapshots = %#v", differences[0])
+		}
+		if strings.Contains(differences[0].Left.YAML+differences[0].Right.YAML, "canary") {
+			t.Fatal("historical replacement diff exposed a sensitive value")
+		}
+	})
+}
+
+func TestDiffReturnsSafeErrorsWithoutRecords(t *testing.T) {
+	valid := diffTestInspection(&document.Node{Kind: document.String, Text: "safe"})
+	for _, test := range []struct {
+		name        string
+		left, right *Inspection
+	}{
+		{name: "nil left", right: valid},
+		{name: "nil right", left: valid},
+		{name: "missing final tree", left: &Inspection{}, right: valid},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			differences, err := Diff(test.left, test.right)
+			if differences != nil || err == nil || err != errDiffInspectionUnavailable || strings.Contains(err.Error(), "safe") {
+				t.Fatalf("differences, err = %#v, %v", differences, err)
+			}
+		})
+	}
+}
+
+func TestDiffSerializationErrorDoesNotExposeWriterDetails(t *testing.T) {
+	err := writeDiffDocument(diffErrorWriter{}, &document.Node{Kind: document.String, Text: "safe"})
+	if err != errDiffSnapshotUnavailable || strings.Contains(err.Error(), "CANARY") {
+		t.Fatalf("serialization error = %v", err)
+	}
+}
+
+type diffErrorWriter struct{}
+
+func (diffErrorWriter) Write([]byte) (int, error) {
+	return 0, errors.New("CANARY_WRITER_ERROR")
+}

internal/engine/diff_sensitivity.go

@@ -0,0 +1,48 @@
+package engine
+
+type diffSensitivity struct {
+	prefixes pathPrefixIndex
+	pointers []string
+}
+
+func newDiffSensitivity(left, right map[string]bool) *diffSensitivity {
+	sensitivity := &diffSensitivity{}
+	seen := make(map[string]struct{}, len(left)+len(right))
+	for _, classifications := range []map[string]bool{left, right} {
+		for pointer, classified := range classifications {
+			if !classified {
+				continue
+			}
+			if _, found := seen[pointer]; found {
+				continue
+			}
+			seen[pointer] = struct{}{}
+			id := len(sensitivity.pointers)
+			sensitivity.pointers = append(sensitivity.pointers, pointer)
+			sensitivity.prefixes.insert(pointer, id)
+		}
+	}
+	return sensitivity
+}
+
+func (sensitivity *diffSensitivity) isSensitiveAtOrAbove(pointer string) bool {
+	if sensitivity == nil {
+		return false
+	}
+	found := false
+	sensitivity.prefixes.visitAncestors(pointer, func(int) { found = true })
+	return found
+}
+
+func (sensitivity *diffSensitivity) hasStrictDescendant(pointer string) bool {
+	if sensitivity == nil {
+		return false
+	}
+	found := false
+	sensitivity.prefixes.visitDescendants(pointer, func(id int) {
+		if sensitivity.pointers[id] != pointer {
+			found = true
+		}
+	})
+	return found
+}

internal/engine/diff_sensitivity_test.go

@@ -0,0 +1,90 @@
+package engine
+
+import (
+	"maps"
+	"testing"
+)
+
+func TestDiffSensitivityCombinesClassificationsWithoutMutation(t *testing.T) {
+	left := map[string]bool{
+		"/a":                  true,
+		"/a/b":                true,
+		"/historical/removed": true,
+		"/cross~1key":         true,
+		"/literal~01slash":    true,
+		"/items/01":           true,
+		"/items/+1":           false,
+		"/false-left":         false,
+	}
+	right := map[string]bool{
+		"/a/b":         true,
+		"/right-only":  true,
+		"/false-right": false,
+	}
+	leftBefore, rightBefore := maps.Clone(left), maps.Clone(right)
+	sensitivity := newDiffSensitivity(left, right)
+
+	for _, test := range []struct {
+		pointer string
+		want    bool
+	}{
+		{pointer: "/a", want: true},
+		{pointer: "/a/b", want: true},
+		{pointer: "/a/b/c", want: true},
+		{pointer: "/ab", want: false},
+		{pointer: "/ab/c", want: false},
+		{pointer: "/historical/removed", want: true},
+		{pointer: "/historical/removed/child", want: true},
+		{pointer: "/historical", want: false},
+		{pointer: "/right-only", want: true},
+		{pointer: "/false-left", want: false},
+		{pointer: "/false-right", want: false},
+		{pointer: "/cross~1key", want: true},
+		{pointer: "/cross/key", want: false},
+		{pointer: "/literal~01slash", want: true},
+		{pointer: "/literal~1slash", want: false},
+		{pointer: "/items/01", want: true},
+		{pointer: "/items/1", want: false},
+		{pointer: "/items/+1", want: false},
+	} {
+		if got := sensitivity.isSensitiveAtOrAbove(test.pointer); got != test.want {
+			t.Errorf("isSensitiveAtOrAbove(%q) = %v, want %v", test.pointer, got, test.want)
+		}
+	}
+
+	for _, test := range []struct {
+		pointer string
+		want    bool
+	}{
+		{pointer: "", want: true},
+		{pointer: "/a", want: true},
+		{pointer: "/a/b", want: false},
+		{pointer: "/ab", want: false},
+		{pointer: "/historical", want: true},
+		{pointer: "/right-only", want: false},
+		{pointer: "/cross~1key", want: false},
+	} {
+		if got := sensitivity.hasStrictDescendant(test.pointer); got != test.want {
+			t.Errorf("hasStrictDescendant(%q) = %v, want %v", test.pointer, got, test.want)
+		}
+	}
+
+	if !maps.Equal(left, leftBefore) || !maps.Equal(right, rightBefore) {
+		t.Fatal("classification maps were modified")
+	}
+}
+
+func TestDiffSensitivityDistinguishesRootAndEmptyKey(t *testing.T) {
+	root := newDiffSensitivity(map[string]bool{"": true}, nil)
+	if !root.isSensitiveAtOrAbove("") || !root.isSensitiveAtOrAbove("/empty") ||
+		root.hasStrictDescendant("") {
+		t.Fatal("root classification did not remain distinct from strict descendants")
+	}
+
+	emptyKey := newDiffSensitivity(map[string]bool{"/": true}, nil)
+	if emptyKey.isSensitiveAtOrAbove("") || !emptyKey.isSensitiveAtOrAbove("/") ||
+		emptyKey.isSensitiveAtOrAbove("/other") || !emptyKey.hasStrictDescendant("") ||
+		emptyKey.hasStrictDescendant("/") {
+		t.Fatal("empty-key classification was treated as the root or an unrelated path")
+	}
+}

internal/engine/diff_snapshot.go

@@ -0,0 +1,195 @@
+package engine
+
+import (
+	"sort"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type pairedDiffSnapshot struct {
+	left             *document.Node
+	right            *document.Node
+	leftRedacted     bool
+	rightRedacted    bool
+	requiresFallback bool
+	hiddenChanged    bool
+}
+
+func preparePairedDiffSnapshot(left, right *document.Node, path Path, sensitivity *diffSensitivity) (pairedDiffSnapshot, bool) {
+	paired, supported := preparePairedDiffNodes(left, right, path, sensitivity)
+	if !supported || !paired.requiresFallback {
+		return paired, supported
+	}
+	return pairedDiffSnapshot{
+		left:          redactedDiffNode(left),
+		right:         redactedDiffNode(right),
+		leftRedacted:  left != nil,
+		rightRedacted: right != nil,
+		hiddenChanged: true,
+	}, true
+}
+
+func preparePairedDiffNodes(left, right *document.Node, path Path, sensitivity *diffSensitivity) (pairedDiffSnapshot, bool) {
+	if left == nil && right == nil {
+		return pairedDiffSnapshot{}, true
+	}
+	if sensitivity.isSensitiveAtOrAbove(path.String()) {
+		return pairedDiffSnapshot{
+			left:          redactedDiffNode(left),
+			right:         redactedDiffNode(right),
+			leftRedacted:  left != nil,
+			rightRedacted: right != nil,
+			hiddenChanged: !configurationValuesEqual(left, right),
+		}, true
+	}
+	if left != nil && right != nil && left.Kind != right.Kind {
+		if sensitivity.hasStrictDescendant(path.String()) {
+			return pairedDiffSnapshot{requiresFallback: true}, true
+		}
+		return pairedDiffSnapshot{left: left, right: right}, true
+	}
+
+	kind := document.Null
+	if left != nil {
+		kind = left.Kind
+	} else if right != nil {
+		kind = right.Kind
+	}
+	switch kind {
+	case document.Mapping:
+		return preparePairedDiffMapping(left, right, path, sensitivity)
+	case document.Sequence:
+		return preparePairedDiffSequence(left, right, path, sensitivity)
+	default:
+		return pairedDiffSnapshot{left: left, right: right}, true
+	}
+}
+
+func preparePairedDiffMapping(left, right *document.Node, path Path, sensitivity *diffSensitivity) (pairedDiffSnapshot, bool) {
+	leftEntries := diffMappingEntries(left)
+	rightEntries := diffMappingEntries(right)
+	keys := make([]string, 0, len(leftEntries)+len(rightEntries))
+	seen := make(map[string]struct{}, len(leftEntries)+len(rightEntries))
+	for key := range leftEntries {
+		seen[key] = struct{}{}
+		keys = append(keys, key)
+	}
+	for key := range rightEntries {
+		if _, found := seen[key]; found {
+			continue
+		}
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+
+	var leftCopy, rightCopy *document.Node
+	if left != nil {
+		copy := *left
+		copy.Mapping = make([]document.Entry, 0, len(left.Mapping))
+		leftCopy = &copy
+	}
+	if right != nil {
+		copy := *right
+		copy.Mapping = make([]document.Entry, 0, len(right.Mapping))
+		rightCopy = &copy
+	}
+	redacted := pairedDiffSnapshot{}
+	for _, key := range keys {
+		leftEntry, leftPresent := leftEntries[key]
+		rightEntry, rightPresent := rightEntries[key]
+		var leftChild, rightChild *document.Node
+		if leftPresent {
+			leftChild = leftEntry.Value
+		}
+		if rightPresent {
+			rightChild = rightEntry.Value
+		}
+		child, supported := preparePairedDiffNodes(leftChild, rightChild, path.Key(key), sensitivity)
+		if !supported {
+			return pairedDiffSnapshot{}, false
+		}
+		if child.requiresFallback {
+			return pairedDiffSnapshot{requiresFallback: true}, true
+		}
+		if leftPresent {
+			leftEntry.Value = child.left
+			leftCopy.Mapping = append(leftCopy.Mapping, leftEntry)
+		}
+		if rightPresent {
+			rightEntry.Value = child.right
+			rightCopy.Mapping = append(rightCopy.Mapping, rightEntry)
+		}
+		redacted.leftRedacted = redacted.leftRedacted || child.leftRedacted
+		redacted.rightRedacted = redacted.rightRedacted || child.rightRedacted
+		redacted.hiddenChanged = redacted.hiddenChanged || child.hiddenChanged
+	}
+	redacted.left = leftCopy
+	redacted.right = rightCopy
+	return redacted, true
+}
+
+func preparePairedDiffSequence(left, right *document.Node, path Path, sensitivity *diffSensitivity) (pairedDiffSnapshot, bool) {
+	var leftCopy, rightCopy *document.Node
+	if left != nil {
+		copy := *left
+		copy.Sequence = make([]*document.Node, len(left.Sequence))
+		leftCopy = &copy
+	}
+	if right != nil {
+		copy := *right
+		copy.Sequence = make([]*document.Node, len(right.Sequence))
+		rightCopy = &copy
+	}
+	length := 0
+	if left != nil {
+		length = len(left.Sequence)
+	}
+	if right != nil && len(right.Sequence) > length {
+		length = len(right.Sequence)
+	}
+	result := pairedDiffSnapshot{left: leftCopy, right: rightCopy}
+	for index := 0; index < length; index++ {
+		var leftChild, rightChild *document.Node
+		if left != nil && index < len(left.Sequence) {
+			leftChild = left.Sequence[index]
+		}
+		if right != nil && index < len(right.Sequence) {
+			rightChild = right.Sequence[index]
+		}
+		child, supported := preparePairedDiffNodes(leftChild, rightChild, path.Index(index), sensitivity)
+		if !supported {
+			return pairedDiffSnapshot{}, false
+		}
+		if child.requiresFallback {
+			return pairedDiffSnapshot{requiresFallback: true}, true
+		}
+		if left != nil && index < len(left.Sequence) {
+			leftCopy.Sequence[index] = child.left
+		}
+		if right != nil && index < len(right.Sequence) {
+			rightCopy.Sequence[index] = child.right
+		}
+		result.leftRedacted = result.leftRedacted || child.leftRedacted
+		result.rightRedacted = result.rightRedacted || child.rightRedacted
+		result.hiddenChanged = result.hiddenChanged || child.hiddenChanged
+	}
+	return result, true
+}
+
+func diffMappingEntries(node *document.Node) map[string]document.Entry {
+	entries := make(map[string]document.Entry)
+	if node == nil {
+		return entries
+	}
+	for _, entry := range node.Mapping {
+		entries[entry.Key] = entry
+	}
+	return entries
+}
+
+func redactedDiffNode(node *document.Node) *document.Node {
+	if node == nil {
+		return nil
+	}
+	return &document.Node{Kind: document.String, Text: "[REDACTED]"}
+}

internal/engine/diff_snapshot_test.go

@@ -0,0 +1,351 @@
+package engine
+
+import (
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestPreparePairedDiffSnapshotRedactsAlignedMappingFromEitherSide(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "credential: alpha\npublic: before\n")
+	right := parseCompositionDocument(t, "right", "credential: bravo\npublic: after\n")
+	sensitivity := newDiffSensitivity(map[string]bool{"/credential": true}, nil)
+
+	paired, supported := preparePairedDiffSnapshot(left, right, Path{}, sensitivity)
+	if !supported {
+		t.Fatal("compatible mappings were not supported")
+	}
+	if !paired.leftRedacted || !paired.rightRedacted {
+		t.Fatalf("redacted flags = %v, %v; want true on both sides", paired.leftRedacted, paired.rightRedacted)
+	}
+	assertDiffStringNode(t, mappingValue(t, paired.left, "credential"), "[REDACTED]")
+	assertDiffStringNode(t, mappingValue(t, paired.right, "credential"), "[REDACTED]")
+	assertDiffStringNode(t, mappingValue(t, paired.left, "public"), "before")
+	assertDiffStringNode(t, mappingValue(t, paired.right, "public"), "after")
+	assertDiffStringNode(t, mappingValue(t, left, "credential"), "alpha")
+	assertDiffStringNode(t, mappingValue(t, right, "credential"), "bravo")
+	if paired.left == left || paired.right == right || &paired.left.Mapping[0] == &left.Mapping[0] {
+		t.Fatal("safe mapping containers or entries share mutable storage with retained trees")
+	}
+}
+
+func TestPreparePairedDiffSnapshotPreservesSequencePositionsAndLengths(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "items: [left-public, hidden, old-tail]\n")
+	right := parseCompositionDocument(t, "right", "items: [right-public, hidden, old-tail, extra]\n")
+	sensitivity := newDiffSensitivity(nil, map[string]bool{"/items/1": true})
+
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "items"), mappingValue(t, right, "items"), Keys("items"), sensitivity,
+	)
+	if !supported {
+		t.Fatal("compatible sequences were not supported")
+	}
+	if !paired.leftRedacted || !paired.rightRedacted {
+		t.Fatalf("redacted flags = %v, %v; want true on both sides", paired.leftRedacted, paired.rightRedacted)
+	}
+	if len(paired.left.Sequence) != 3 || len(paired.right.Sequence) != 4 {
+		t.Fatalf("sequence lengths = %d, %d; want 3, 4", len(paired.left.Sequence), len(paired.right.Sequence))
+	}
+	assertDiffStringNode(t, paired.left.Sequence[0], "left-public")
+	assertDiffStringNode(t, paired.right.Sequence[0], "right-public")
+	assertDiffStringNode(t, paired.left.Sequence[1], "[REDACTED]")
+	assertDiffStringNode(t, paired.right.Sequence[1], "[REDACTED]")
+	assertDiffStringNode(t, paired.right.Sequence[3], "extra")
+	assertDiffStringNode(t, mappingValue(t, left, "items").Sequence[1], "hidden")
+	if &paired.left.Sequence[0] == &mappingValue(t, left, "items").Sequence[0] {
+		t.Fatal("safe sequence shares mutable storage with retained tree")
+	}
+}
+
+func TestPreparePairedDiffSnapshotMasksSensitiveDescendantsOfAbsentSubtrees(t *testing.T) {
+	tests := []struct {
+		name        string
+		left, right string
+		absentSide  string
+	}{
+		{
+			name:       "removed subtree",
+			left:       "removed: {token: old-secret, public: retained}\n",
+			right:      "other: value\n",
+			absentSide: "right",
+		},
+		{
+			name:       "added subtree",
+			left:       "other: value\n",
+			right:      "added: {token: new-secret, public: retained}\n",
+			absentSide: "left",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			left := parseCompositionDocument(t, "left", test.left)
+			right := parseCompositionDocument(t, "right", test.right)
+			paired, supported := preparePairedDiffSnapshot(
+				mappingValueIfPresent(left, "removed", "added"),
+				mappingValueIfPresent(right, "removed", "added"),
+				Keys("subtree"),
+				newDiffSensitivity(map[string]bool{"/subtree/token": true}, nil),
+			)
+			if !supported {
+				t.Fatal("compatible subtree and absence were not supported")
+			}
+			if test.absentSide == "left" {
+				if paired.left != nil || paired.leftRedacted || !paired.rightRedacted {
+					t.Fatalf("paired absence/redaction = %#v", paired)
+				}
+				assertDiffStringNode(t, mappingValue(t, paired.right, "token"), "[REDACTED]")
+				assertDiffStringNode(t, mappingValue(t, paired.right, "public"), "retained")
+			} else {
+				if paired.right != nil || paired.rightRedacted || !paired.leftRedacted {
+					t.Fatalf("paired absence/redaction = %#v", paired)
+				}
+				assertDiffStringNode(t, mappingValue(t, paired.left, "token"), "[REDACTED]")
+				assertDiffStringNode(t, mappingValue(t, paired.left, "public"), "retained")
+			}
+		})
+	}
+}
+
+func TestPreparePairedDiffSnapshotMasksSelectedRootAndContainer(t *testing.T) {
+	tests := []struct {
+		name        string
+		left, right *document.Node
+		path        Path
+		selector    string
+	}{
+		{
+			name:     "root",
+			left:     parseCompositionDocument(t, "left", "token: old\n"),
+			right:    parseCompositionDocument(t, "right", "token: new\n"),
+			path:     Path{},
+			selector: "",
+		},
+		{
+			name:     "container",
+			left:     parseCompositionDocument(t, "left", "group: {public: old}\n"),
+			right:    parseCompositionDocument(t, "right", "group: {public: new}\n"),
+			path:     Keys("group"),
+			selector: "/group",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			paired, supported := preparePairedDiffSnapshot(
+				test.left, test.right, test.path,
+				newDiffSensitivity(map[string]bool{test.selector: true}, nil),
+			)
+			if !supported {
+				t.Fatal("selected nodes were not supported")
+			}
+			if !paired.leftRedacted || !paired.rightRedacted {
+				t.Fatalf("redacted flags = %v, %v; want true on both sides", paired.leftRedacted, paired.rightRedacted)
+			}
+			assertDiffStringNode(t, paired.left, "[REDACTED]")
+			assertDiffStringNode(t, paired.right, "[REDACTED]")
+		})
+	}
+}
+
+func TestPreparePairedDiffSnapshotDoesNotInterpretMarkerLookingInput(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "label: '[REDACTED]'\n")
+	right := parseCompositionDocument(t, "right", "label: '[REDACTED]'\n")
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "label"), mappingValue(t, right, "label"), Keys("label"),
+		newDiffSensitivity(nil, nil),
+	)
+	if !supported {
+		t.Fatal("ordinary scalar values were not supported")
+	}
+	if paired.leftRedacted || paired.rightRedacted {
+		t.Fatalf("redacted flags = %v, %v; want false", paired.leftRedacted, paired.rightRedacted)
+	}
+	if paired.left != mappingValue(t, left, "label") || paired.right != mappingValue(t, right, "label") {
+		t.Fatal("unselected scalar nodes should remain borrowed immutable nodes")
+	}
+	assertDiffStringNode(t, paired.left, "[REDACTED]")
+	assertDiffStringNode(t, paired.right, "[REDACTED]")
+}
+
+func TestPreparePairedDiffSnapshotMasksSensitiveStructuralReplacements(t *testing.T) {
+	tests := []struct {
+		name        string
+		left, right string
+		path        Path
+		selector    string
+	}{
+		{
+			name:     "mapping to scalar",
+			left:     "changed: {token: old-secret, public: old}\n",
+			right:    "changed: new-scalar\n",
+			path:     Keys("changed"),
+			selector: "/changed/token",
+		},
+		{
+			name:     "mapping to scalar with historical-only descendant",
+			left:     "changed: {public: old}\n",
+			right:    "changed: new-scalar\n",
+			path:     Keys("changed"),
+			selector: "/changed/removed/secret",
+		},
+		{
+			name:     "scalar to mapping",
+			left:     "changed: old-scalar\n",
+			right:    "changed: {token: new-secret, public: new}\n",
+			path:     Keys("changed"),
+			selector: "/changed/token",
+		},
+		{
+			name:     "mapping to sequence with numeric paths",
+			left:     "changed: {'0': {token: old-secret}}\n",
+			right:    "changed: [{token: new-secret}]\n",
+			path:     Keys("changed"),
+			selector: "/changed/0/token",
+		},
+		{
+			name:     "sequence to mapping with numeric paths",
+			left:     "changed: [{token: old-secret}]\n",
+			right:    "changed: {'0': {token: new-secret}}\n",
+			path:     Keys("changed"),
+			selector: "/changed/0/token",
+		},
+		{
+			name:     "null to container",
+			left:     "changed: null\n",
+			right:    "changed: {token: new-secret}\n",
+			path:     Keys("changed"),
+			selector: "/changed/token",
+		},
+		{
+			name:     "container to null",
+			left:     "changed: {token: old-secret}\n",
+			right:    "changed: null\n",
+			path:     Keys("changed"),
+			selector: "/changed/token",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			leftRoot := parseCompositionDocument(t, "left", test.left)
+			rightRoot := parseCompositionDocument(t, "right", test.right)
+			left := mappingValue(t, leftRoot, test.path.segments[0].key)
+			right := mappingValue(t, rightRoot, test.path.segments[0].key)
+			paired, supported := preparePairedDiffSnapshot(
+				left, right, test.path, newDiffSensitivity(nil, map[string]bool{test.selector: true}),
+			)
+			assertWholeRegionFallback(t, paired, supported, left, right)
+		})
+	}
+}
+
+func TestPreparePairedDiffSnapshotMasksOriginalRegionForNestedSequenceMismatch(t *testing.T) {
+	leftRoot := parseCompositionDocument(t, "left", "items: [{branch: {token: old-secret, public: old}}]\n")
+	rightRoot := parseCompositionDocument(t, "right", "items: [{branch: new-scalar}]\n")
+	left := mappingValue(t, leftRoot, "items")
+	right := mappingValue(t, rightRoot, "items")
+	paired, supported := preparePairedDiffSnapshot(
+		left, right, Keys("items"), newDiffSensitivity(nil, map[string]bool{"/items/0/branch/token": true}),
+	)
+	assertWholeRegionFallback(t, paired, supported, left, right)
+}
+
+func TestPreparePairedDiffSnapshotKeepsPublicScalarsWithHistoricalDescendants(t *testing.T) {
+	leftRoot := parseCompositionDocument(t, "left", "changed: before\n")
+	rightRoot := parseCompositionDocument(t, "right", "changed: after\n")
+	left := mappingValue(t, leftRoot, "changed")
+	right := mappingValue(t, rightRoot, "changed")
+	paired, supported := preparePairedDiffSnapshot(
+		left, right, Keys("changed"), newDiffSensitivity(map[string]bool{"/changed/removed/secret": true}, nil),
+	)
+	if !supported || paired.leftRedacted || paired.rightRedacted || paired.hiddenChanged {
+		t.Fatalf("public scalar replacement = %#v, supported=%v", paired, supported)
+	}
+	assertDiffStringNode(t, paired.left, "before")
+	assertDiffStringNode(t, paired.right, "after")
+}
+
+func TestPreparePairedDiffSnapshotKeepsPublicContentAcrossAbsence(t *testing.T) {
+	right := parseCompositionDocument(t, "right", "branch: scalar\n")
+	paired, supported := preparePairedDiffSnapshot(
+		nil, right, Keys("added"), newDiffSensitivity(nil, map[string]bool{"/added/branch/secret": true}),
+	)
+	if !supported || paired.left != nil || paired.leftRedacted || paired.rightRedacted || paired.hiddenChanged {
+		t.Fatalf("public addition presence/redaction = %#v, supported=%v", paired, supported)
+	}
+	assertDiffStringNode(t, mappingValue(t, paired.right, "branch"), "scalar")
+}
+
+func TestPreparePairedDiffSnapshotPreservesPublicReplacementBesideSensitiveSibling(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "child: before\n")
+	right := &document.Node{Kind: document.String, Text: "after"}
+	paired, supported := preparePairedDiffSnapshot(
+		mappingValue(t, left, "child"), right, Keys("public"),
+		newDiffSensitivity(nil, map[string]bool{"/private/token": true}),
+	)
+	if !supported || paired.left != mappingValue(t, left, "child") || paired.right != right || paired.leftRedacted || paired.rightRedacted {
+		t.Fatalf("unrelated classification changed public replacement: %#v, supported=%v", paired, supported)
+	}
+}
+
+func TestPreparePairedDiffSnapshotTargetsRedactionAcrossAbsence(t *testing.T) {
+	left := parseCompositionDocument(t, "left", "items: []\n")
+	right := parseCompositionDocument(t, "right", "items: [{token: new-secret, public: visible}]\n")
+	leftItems := mappingValue(t, left, "items")
+	rightItems := mappingValue(t, right, "items")
+	paired, supported := preparePairedDiffSnapshot(
+		leftItems, rightItems, Keys("items"), newDiffSensitivity(nil, map[string]bool{"/items/0/token": true}),
+	)
+	if !supported || paired.left == nil || paired.right == nil || paired.leftRedacted || !paired.rightRedacted {
+		t.Fatalf("targeted sequence redaction = %#v, supported=%v", paired, supported)
+	}
+	if len(paired.left.Sequence) != 0 || len(paired.right.Sequence) != 1 {
+		t.Fatalf("sequence lengths = %d, %d; want 0, 1", len(paired.left.Sequence), len(paired.right.Sequence))
+	}
+	assertDiffStringNode(t, mappingValue(t, paired.right.Sequence[0], "token"), "[REDACTED]")
+	assertDiffStringNode(t, mappingValue(t, paired.right.Sequence[0], "public"), "visible")
+}
+
+func assertWholeRegionFallback(t *testing.T, paired pairedDiffSnapshot, supported bool, left, right *document.Node) {
+	t.Helper()
+	if !supported {
+		t.Fatal("sensitive incompatible shape was not handled")
+	}
+	if !paired.hiddenChanged {
+		t.Fatal("fallback for a changed reported region did not mark hidden change")
+	}
+	if (left == nil) != (paired.left == nil) || (right == nil) != (paired.right == nil) {
+		t.Fatalf("fallback changed root presence: %#v", paired)
+	}
+	if left != nil {
+		assertDiffStringNode(t, paired.left, "[REDACTED]")
+		if !paired.leftRedacted {
+			t.Fatal("present left region was not marked redacted")
+		}
+	}
+	if right != nil {
+		assertDiffStringNode(t, paired.right, "[REDACTED]")
+		if !paired.rightRedacted {
+			t.Fatal("present right region was not marked redacted")
+		}
+	}
+}
+
+func mappingValueIfPresent(node *document.Node, keys ...string) *document.Node {
+	if node == nil {
+		return nil
+	}
+	for _, key := range keys {
+		for _, entry := range node.Mapping {
+			if entry.Key == key {
+				return entry.Value
+			}
+		}
+	}
+	return nil
+}
+
+func assertDiffStringNode(t *testing.T, node *document.Node, want string) {
+	t.Helper()
+	if node == nil || node.Kind != document.String || node.Text != want {
+		t.Fatalf("node = %#v, want string %q", node, want)
+	}
+}

internal/engine/diff_test.go

@@ -0,0 +1,144 @@
+package engine
+
+import (
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestPrepareDiffRegionsUsesCanonicalConfigurationComparison(t *testing.T) {
+	tests := []struct {
+		name  string
+		left  string
+		right string
+		want  []expectedDiffRegion
+	}{
+		{
+			name:  "mapping order is ignored for equal values",
+			left:  "first: 1\nsecond: true\n",
+			right: "second: true\nfirst: 1\n",
+		},
+		{
+			name:  "addition removal null and empty values",
+			left:  "removed: null\n",
+			right: "added: null\nempty_map: {}\nempty_sequence: []\n",
+			want: []expectedDiffRegion{
+				{path: "/added", rightKind: document.Null, rightPresent: true},
+				{path: "/empty_map", rightKind: document.Mapping, rightPresent: true},
+				{path: "/empty_sequence", rightKind: document.Sequence, rightPresent: true},
+				{path: "/removed", leftKind: document.Null, leftPresent: true},
+			},
+		},
+		{
+			name:  "scalar kinds and atomic sequences",
+			left:  "scalar: 1\nitems: [one, two]\n",
+			right: "scalar: '1'\nitems: [one, changed]\n",
+			want: []expectedDiffRegion{
+				{path: "/items", leftKind: document.Sequence, rightKind: document.Sequence, leftPresent: true, rightPresent: true},
+				{path: "/scalar", leftKind: document.Number, rightKind: document.String, leftPresent: true, rightPresent: true},
+			},
+		},
+		{
+			name:  "escaped empty and numeric mapping keys sort by pointer",
+			left:  `"": old` + "\n'0': old\n'01': old\n'a/b': old\n'a~b': old\n",
+			right: `"": new` + "\n'0': new\n'01': new\n'a/b': new\n'a~b': new\n",
+			want: []expectedDiffRegion{
+				{path: "/", leftKind: document.String, rightKind: document.String, leftPresent: true, rightPresent: true},
+				{path: "/0", leftKind: document.String, rightKind: document.String, leftPresent: true, rightPresent: true},
+				{path: "/01", leftKind: document.String, rightKind: document.String, leftPresent: true, rightPresent: true},
+				{path: "/a~0b", leftKind: document.String, rightKind: document.String, leftPresent: true, rightPresent: true},
+				{path: "/a~1b", leftKind: document.String, rightKind: document.String, leftPresent: true, rightPresent: true},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			leftRoot := parseCompositionDocument(t, "left", test.left)
+			rightRoot := parseCompositionDocument(t, "right", test.right)
+			regions, err := prepareDiffRegions(diffTestInspection(leftRoot), diffTestInspection(rightRoot))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(regions) != len(test.want) {
+				t.Fatalf("regions = %#v, want %#v", regions, test.want)
+			}
+			for index, want := range test.want {
+				region := regions[index]
+				if region.path.String() != want.path {
+					t.Fatalf("region[%d].path = %q, want %q", index, region.path.String(), want.path)
+				}
+				assertDiffRegionNode(t, "left", region.left, want.leftPresent, want.leftKind)
+				assertDiffRegionNode(t, "right", region.right, want.rightPresent, want.rightKind)
+			}
+		})
+	}
+}
+
+func TestPrepareDiffRegionsHandlesRootReplacementAndBorrowsNodes(t *testing.T) {
+	leftRoot := &document.Node{Kind: document.String, Text: "before"}
+	rightRoot := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{
+		Key: "value", Value: &document.Node{Kind: document.Number, Text: "1"},
+	}}}
+	regions, err := prepareDiffRegions(diffTestInspection(leftRoot), diffTestInspection(rightRoot))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(regions) != 1 || regions[0].path.String() != "" || regions[0].left != leftRoot || regions[0].right != rightRoot {
+		t.Fatalf("root region = %#v", regions)
+	}
+
+	leftRoot = parseCompositionDocument(t, "left-child", "value: before\n")
+	rightRoot = parseCompositionDocument(t, "right-child", "value: after\n")
+	regions, err = prepareDiffRegions(diffTestInspection(leftRoot), diffTestInspection(rightRoot))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(regions) != 1 || regions[0].left != mappingValue(t, leftRoot, "value") || regions[0].right != mappingValue(t, rightRoot, "value") {
+		t.Fatalf("child nodes were not borrowed from the frozen trees: %#v", regions)
+	}
+}
+
+func TestPrepareDiffRegionsRejectsUnavailableInspections(t *testing.T) {
+	valid := diffTestInspection(&document.Node{Kind: document.String, Text: "safe"})
+	tests := []struct {
+		name        string
+		left, right *Inspection
+	}{
+		{name: "nil left", left: nil, right: valid},
+		{name: "nil right", left: valid, right: nil},
+		{name: "missing left tree", left: &Inspection{}, right: valid},
+		{name: "missing right tree", left: valid, right: &Inspection{}},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			regions, err := prepareDiffRegions(test.left, test.right)
+			if err == nil || regions != nil {
+				t.Fatalf("regions, err = %#v, %v", regions, err)
+			}
+		})
+	}
+}
+
+type expectedDiffRegion struct {
+	path                      string
+	leftKind, rightKind       document.Kind
+	leftPresent, rightPresent bool
+}
+
+func diffTestInspection(root *document.Node) *Inspection {
+	return &Inspection{final: root, immutableLookup: buildDocumentLookup(root)}
+}
+
+func assertDiffRegionNode(t *testing.T, side string, node *document.Node, wantPresent bool, wantKind document.Kind) {
+	t.Helper()
+	if !wantPresent {
+		if node != nil {
+			t.Fatalf("%s node = %#v, want absence", side, node)
+		}
+		return
+	}
+	if node == nil || node.Kind != wantKind {
+		t.Fatalf("%s node = %#v, want kind %v", side, node, wantKind)
+	}
+}

internal/engine/document_compare.go

@@ -24,12 +24,23 @@ type documentDelta struct {
 func compareConfigurationValues(before, after *document.Node) []documentDelta {
 	var deltas []documentDelta
 	compareConfigurationValue(before, after, Path{}, &deltas)
-	slices.SortFunc(deltas, func(left, right documentDelta) int {
+	type orderedDelta struct {
-		if order := cmp.Compare(left.path.String(), right.path.String()); order != 0 {
+		delta   documentDelta
+		pointer string
+	}
+	ordered := make([]orderedDelta, len(deltas))
+	for i, delta := range deltas {
+		ordered[i] = orderedDelta{delta: delta, pointer: delta.path.String()}
+	}
+	slices.SortFunc(ordered, func(left, right orderedDelta) int {
+		if order := cmp.Compare(left.pointer, right.pointer); order != 0 {
 			return order
 		}
-		return int(left.kind) - int(right.kind)
+		return int(left.delta.kind) - int(right.delta.kind)
 	})
+	for i, item := range ordered {
+		deltas[i] = item.delta
+	}
 	return deltas
 }
 

internal/engine/document_lookup.go

@@ -0,0 +1,54 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+// documentLookup contains read-only mapping positions for a completed document.
+type documentLookup struct {
+	byNode map[*document.Node]map[string]int
+}
+
+func buildDocumentLookup(roots ...*document.Node) *documentLookup {
+	lookup := &documentLookup{byNode: make(map[*document.Node]map[string]int)}
+	visited := make(map[*document.Node]struct{})
+	var visit func(*document.Node)
+	visit = func(node *document.Node) {
+		if node == nil {
+			return
+		}
+		if _, ok := visited[node]; ok {
+			return
+		}
+		visited[node] = struct{}{}
+		switch node.Kind {
+		case document.Mapping:
+			entries := make(map[string]int, len(node.Mapping))
+			for index, entry := range node.Mapping {
+				if _, exists := entries[entry.Key]; !exists {
+					entries[entry.Key] = index
+				}
+				visit(entry.Value)
+			}
+			lookup.byNode[node] = entries
+		case document.Sequence:
+			for _, child := range node.Sequence {
+				visit(child)
+			}
+		}
+	}
+	for _, root := range roots {
+		visit(root)
+	}
+	return lookup
+}
+
+func (lookup *documentLookup) find(node *document.Node, key string) int {
+	if lookup == nil {
+		return -1
+	}
+	if entries := lookup.byNode[node]; entries != nil {
+		if index, ok := entries[key]; ok {
+			return index
+		}
+	}
+	return -1
+}

internal/engine/document_walk.go

@@ -31,6 +31,10 @@ func indexDocument(node *document.Node, path Path, index map[string]*document.No
 }
 
 func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
+	return documentAtPathWithLookup(root, path, nil)
+}
+
+func documentAtPathWithLookup(root *document.Node, path Path, lookup *documentLookup) (*document.Node, bool) {
 	if root == nil || !path.valid() {
 		return nil, false
 	}
@@ -41,17 +45,21 @@ func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
 			if segment.kind == pathSegmentIndex {
 				return nil, false
 			}
-			found := false
+			entryIndex := -1
-			for _, entry := range current.Mapping {
+			if lookup != nil {
+				entryIndex = lookup.find(current, segment.key)
+			} else {
+				for index, entry := range current.Mapping {
 					if entry.Key == segment.key {
-					current = entry.Value
+						entryIndex = index
-					found = true
 						break
 					}
 				}
-			if !found {
+			}
+			if entryIndex < 0 || entryIndex >= len(current.Mapping) {
 				return nil, false
 			}
+			current = current.Mapping[entryIndex].Value
 		case document.Sequence:
 			index, ok := schemaIndex(segment)
 			if !ok || index >= len(current.Sequence) {

internal/engine/explain.go

@@ -40,7 +40,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	if r == nil || r.final == nil || r.baseline == nil || !r.metadata.hasHistoricalPath(path) {
 		return Explanation{}, false
 	}
-	explanation := Explanation{Path: path.clone(), Effective: valueSnapshot(r.final, path, r.secrets)}
+	explanation := Explanation{Path: path.clone(), Effective: valueSnapshotWithLookup(r.final, path, r.secrets, r.immutableLookup)}
 	if info, ok := r.metadata.Lookup(path); ok {
 		explanation.Origin = cloneOrigin(info.Origin)
 	}
@@ -53,7 +53,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	}
 	replayIndex := new(mappingIndex)
 	for _, application := range r.applications {
-		operationPath, relevant := applicationOperationPath(application, path)
+		operationPath, relevant := applicationOperationPath(application, path, r.immutableLookup)
 		var before ValueSnapshot
 		if relevant {
 			before = valueSnapshot(working, path, r.secrets)
@@ -69,7 +69,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 		explanation.History = append(explanation.History, ValueChange{
 			Before: before,
 			After:  after,
-			Origin: historyApplicationOrigin(application, operationPath),
+			Origin: historyApplicationOrigin(application, operationPath, r.immutableLookup),
 		})
 	}
 	appendInheritanceExplanation(&explanation, &working, path, r.inheritance, r.secrets)
@@ -78,20 +78,20 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	// decoding applies them to the final input tree. Show that reconciliation
 	// explicitly, including canonical scalar conversions, before domain changes.
 	replayed, _ := documentAtPath(working, path)
-	decoded, _ := documentAtPath(r.input, path)
+	decoded, _ := documentAtPathWithLookup(r.input, path, r.immutableLookup)
 	if !configurationValuesEqual(replayed, decoded) {
 		origin := cloneOrigin(r.inputOrigins[path.String()])
 		origin.Operation = ChangeDecoding
 		explanation.History = append(explanation.History, ValueChange{
 			Before:  valueSnapshot(working, path, r.secrets),
-			After:   valueSnapshot(r.input, path, r.secrets),
+			After:   valueSnapshotWithLookup(r.input, path, r.secrets, r.immutableLookup),
 			Origin:  origin,
 			Reasons: []string{"applied retained defaults and canonical typed decoding"},
 		})
 	}
 
 	working = document.Clone(r.input)
-	for _, snapshot := range coalescedResolutionSnapshots(r.resolution) {
+	for _, snapshot := range r.resolutionReplay {
 		relevant := pathsIntersect(snapshot.change.Path, path)
 		var before ValueSnapshot
 		if relevant {

internal/engine/explain_test.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
@@ -520,3 +521,95 @@ func TestExplanationReplaysResolutionAdditionsAndOverlappingIntent(t *testing.T)
 		})
 	}
 }
+
+func TestExplanationReplayDescriptorsRemainDetachedAcrossQueries(t *testing.T) {
+	type config struct {
+		Count int `yaml:"count"`
+	}
+	result, err := testLoad(Bytes("resolution-explanation.yml", []byte("count: 1\n")), Options[config]{
+		Definition: Definition[config]{Resolve: func(value *config, resolution *Resolution) error {
+			value.Count = 2
+			resolution.Record(Keys("count"), ChangeNormalization, "normalized", Keys("count"))
+			return nil
+		}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	first, ok := result.Explain(Keys("count"))
+	if !ok {
+		t.Fatal("missing explanation")
+	}
+	var firstResolution *ValueChange
+	for index := range first.History {
+		if first.History[index].Origin.Layer == LayerResolution {
+			firstResolution = &first.History[index]
+			break
+		}
+	}
+	if firstResolution == nil || len(firstResolution.Reasons) != 1 || len(firstResolution.Dependencies) != 1 {
+		t.Fatalf("resolution history = %#v", first.History)
+	}
+	firstResolution.Reasons[0] = "mutated"
+	firstResolution.Dependencies[0].segments[0].key = "mutated"
+
+	second, ok := result.Explain(Keys("count"))
+	if !ok {
+		t.Fatal("missing repeated explanation")
+	}
+	for _, change := range second.History {
+		if change.Origin.Layer == LayerResolution {
+			if !reflect.DeepEqual(change.Reasons, []string{"normalized"}) || len(change.Dependencies) != 1 || change.Dependencies[0].String() != "/count" {
+				t.Fatalf("repeated explanation observed caller mutation: %#v", change)
+			}
+			return
+		}
+	}
+	t.Fatalf("resolution change missing from repeated explanation: %#v", second.History)
+}
+
+func TestConcurrentReadOnlyInspectionQueries(t *testing.T) {
+	type config struct {
+		Group struct {
+			Value string `yaml:"value"`
+		} `yaml:"group"`
+	}
+	result, err := testLoad(Bytes("concurrent-inspection.yml", []byte("group: {value: input}\n")), Options[config]{
+		Definition: Definition[config]{Resolve: func(value *config, resolution *Resolution) error {
+			value.Group.Value = "resolved"
+			resolution.Record(Keys("group", "value"), ChangeNormalization, "normalized", Keys("group", "value"))
+			return nil
+		}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	paths := []Path{Keys("group"), Keys("group", "value")}
+	var wait sync.WaitGroup
+	errors := make(chan string, 8)
+	for worker := 0; worker < cap(errors); worker++ {
+		wait.Add(1)
+		go func() {
+			defer wait.Done()
+			for iteration := 0; iteration < 8; iteration++ {
+				for _, path := range paths {
+					explanation, found := result.Explain(path)
+					if !found || !explanation.Effective.Present {
+						errors <- "missing effective explanation for " + path.String()
+						return
+					}
+					metadata := result.Metadata()
+					if _, found := metadata.Lookup(path); !found || len(metadata.History(path)) == 0 {
+						errors <- "missing metadata for " + path.String()
+						return
+					}
+				}
+			}
+		}()
+	}
+	wait.Wait()
+	close(errors)
+	for message := range errors {
+		t.Error(message)
+	}
+}

internal/engine/history.go

@@ -65,7 +65,7 @@ func cloneHistoryApplications(values []historyApplication) []historyApplication
 	return cloned
 }
 
-func applicationOperationPath(application historyApplication, query Path) (Path, bool) {
+func applicationOperationPath(application historyApplication, query Path, lookup *documentLookup) (Path, bool) {
 	if !application.path.valid() || application.value == nil {
 		return Path{}, false
 	}
@@ -80,7 +80,7 @@ func applicationOperationPath(application historyApplication, query Path) (Path,
 	}
 	for length := 1; length <= len(query.segments); length++ {
 		prefix := Path{segments: clonePathSegments(query.segments[:length], 0)}
-		node, present := documentAtPath(application.value, prefix)
+		node, present := documentAtPathWithLookup(application.value, prefix, lookup)
 		if !present {
 			return Path{}, false
 		}
@@ -91,7 +91,7 @@ func applicationOperationPath(application historyApplication, query Path) (Path,
 	return Path{}, false
 }
 
-func historyApplicationOrigin(application historyApplication, operationPath Path) Origin {
+func historyApplicationOrigin(application historyApplication, operationPath Path, lookup *documentLookup) Origin {
 	if application.origin.Layer != "" {
 		return cloneOrigin(application.origin)
 	}
@@ -100,7 +100,7 @@ func historyApplicationOrigin(application historyApplication, operationPath Path
 	if !ok {
 		return origin
 	}
-	if node, present := documentAtPath(application.value, relative); present {
+	if node, present := documentAtPathWithLookup(application.value, relative, lookup); present {
 		origin.Locations = []Location{publicLocation(node.Location)}
 	}
 	return origin
@@ -179,28 +179,50 @@ func mergeHistoryAtPath(root **document.Node, path Path, incoming *document.Node
 // intent into that event rather than replay a child assignment a second time.
 func coalescedResolutionSnapshots(snapshots []resolutionSnapshot) []resolutionSnapshot {
 	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	reasons := make([]map[string]struct{}, 0, len(snapshots))
+	dependencies := make([]map[string]struct{}, 0, len(snapshots))
+	var coverage pathPrefixIndex
 	for _, snapshot := range snapshots {
-		merged := false
+		pointer := snapshot.change.Path.String()
-		for i := range groups {
+		groupIndex := -1
-			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
+		coverage.visitAncestors(pointer, func(id int) {
-				continue
+			if groupIndex < 0 || id < groupIndex {
+				groupIndex = id
 			}
+		})
+		if groupIndex >= 0 {
+			group := &groups[groupIndex]
 			for _, reason := range snapshot.change.Reasons {
-				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
+				if _, found := reasons[groupIndex][reason]; !found {
+					reasons[groupIndex][reason] = struct{}{}
+					group.change.Reasons = append(group.change.Reasons, reason)
+				}
 			}
 			for _, dependency := range snapshot.change.Dependencies {
-				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
+				dependencyPointer := dependency.String()
+				if _, found := dependencies[groupIndex][dependencyPointer]; !found {
+					dependencies[groupIndex][dependencyPointer] = struct{}{}
+					group.change.Dependencies = append(group.change.Dependencies, dependency.clone())
+				}
 			}
 			if snapshot.change.Origin.Operation == ChangeNormalization {
-				groups[i].change.Origin.Operation = ChangeNormalization
+				group.change.Origin.Operation = ChangeNormalization
 			}
-			merged = true
+			continue
-			break
 		}
-		if !merged {
 		snapshot.change = cloneChange(snapshot.change)
 		groups = append(groups, snapshot)
+		reasonSet := make(map[string]struct{}, len(snapshot.change.Reasons))
+		for _, reason := range snapshot.change.Reasons {
+			reasonSet[reason] = struct{}{}
 		}
+		reasons = append(reasons, reasonSet)
+		dependencySet := make(map[string]struct{}, len(snapshot.change.Dependencies))
+		for _, dependency := range snapshot.change.Dependencies {
+			dependencySet[dependency.String()] = struct{}{}
+		}
+		dependencies = append(dependencies, dependencySet)
+		coverage.insert(pointer, len(groups)-1)
 	}
 	return groups
 }

internal/engine/inheritance_history.go

@@ -1,6 +1,57 @@
 package engine
 
-import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+import (
+	"sort"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type inheritanceHistoryIndex struct {
+	paths pathPrefixIndex
+}
+
+func newInheritanceHistoryIndex(operations []inheritanceOperation) *inheritanceHistoryIndex {
+	if len(operations) == 0 {
+		return nil
+	}
+	index := &inheritanceHistoryIndex{}
+	for operationID, operation := range operations {
+		if operation.control != nil {
+			index.paths.insert(operation.control.path.String(), operationID)
+			continue
+		}
+		if operation.transfer != nil {
+			index.paths.insert(operation.transfer.to.String(), operationID)
+		}
+	}
+	return index
+}
+
+func (index *inheritanceHistoryIndex) matchingOperations(path Path, operations []inheritanceOperation) []inheritanceOperation {
+	if index == nil {
+		return operations
+	}
+	var ids []int
+	seen := make(map[int]struct{})
+	collect := func(id int) {
+		if _, found := seen[id]; found {
+			return
+		}
+		seen[id] = struct{}{}
+		ids = append(ids, id)
+	}
+	pointer := path.String()
+	index.paths.visitAncestors(pointer, collect)
+	index.paths.visitDescendants(pointer, collect)
+	sort.Ints(ids)
+	matching := make([]inheritanceOperation, 0, len(ids))
+	for _, id := range ids {
+		if id >= 0 && id < len(operations) {
+			matching = append(matching, operations[id])
+		}
+	}
+	return matching
+}
 
 // Retain source history at original paths. Structural operations are held once
 // per relationship and projected onto a requested destination path only when

internal/engine/inheritance_history_test.go

@@ -2,6 +2,7 @@ package engine
 
 import (
 	"bytes"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -311,6 +312,51 @@ func TestInheritanceHistoryRetainsControlsAndDisplacedPaths(t *testing.T) {
 	}
 }
 
+func TestIndexedInheritanceHistoryMatchesOperationScan(t *testing.T) {
+	inspection, _ := inheritanceInspectionForTest(t,
+		parseCompositionDocument(t, "source-1", "parent: {branch: {detail: inherited, retained: present}}\n"),
+		parseCompositionDocument(t, "source-2", "child: {extends: parent, branch: replaced}\n"),
+		parseCompositionDocument(t, "source-3", "sibling: {extends: parent}\n"))
+	metadata := inspection.Metadata()
+	if len(metadata.inheritance) < 4 {
+		t.Fatalf("inheritance operations = %d, want multiple control and transfer scopes", len(metadata.inheritance))
+	}
+	queries := []Path{
+		Keys("child"),
+		Keys("child", inheritanceKey),
+		Keys("child", "branch", "detail"),
+		Keys("child", "branch"),
+		Keys("sibling", "branch", "detail"),
+		Path{},
+	}
+	for _, path := range queries {
+		if !metadata.hasHistoricalPath(path) {
+			continue
+		}
+		stored := metadata.history[path.String()]
+		want := historyWithInheritance(path, stored, metadata.inheritance)
+		if got := metadata.History(path); !reflect.DeepEqual(got, want) {
+			t.Errorf("indexed history for %s differs from operation scan:\n got: %#v\nwant: %#v", path, got, want)
+		}
+		unprepared := Metadata{history: metadata.history, historicalPaths: metadata.historicalPaths, inheritance: metadata.inheritance}
+		if got := unprepared.History(path); !reflect.DeepEqual(got, want) {
+			t.Errorf("unprepared history for %s differs from operation scan:\n got: %#v\nwant: %#v", path, got, want)
+		}
+	}
+
+	removed := Keys("child", "branch", "detail")
+	first := metadata.History(removed)
+	if len(first) == 0 || len(first[0].Path.segments) == 0 {
+		t.Fatalf("removed-path history = %#v", first)
+	}
+	first[0].Path.segments[0].key = "mutated"
+	second := cloneMetadata(metadata).History(removed)
+	want := historyWithInheritance(removed, metadata.history[removed.String()], metadata.inheritance)
+	if !reflect.DeepEqual(second, want) {
+		t.Fatalf("returned history mutation affected a repeated or cloned query:\n got: %#v\nwant: %#v", second, want)
+	}
+}
+
 func TestInheritanceHistoryPrecedesApplicationResolution(t *testing.T) {
 	inspection, _ := inheritanceInspectionForTest(t,
 		parseCompositionDocument(t, "source-1", "parent: {value: original}\nchild: {extends: parent}\n"))
@@ -324,6 +370,7 @@ func TestInheritanceHistoryPrecedesApplicationResolution(t *testing.T) {
 	replaceHistoryPath(&final, path, replacement)
 	inspection.final = final
 	inspection.resolution = []resolutionSnapshot{snapshot}
+	inspection.resolutionReplay = coalescedResolutionSnapshots(inspection.resolution)
 	inspection.metadata.history[path.String()] = append(inspection.metadata.history[path.String()], snapshot.change)
 	inspection.metadata.fields[path.String()] = FieldInfo{Explicit: true, Origin: snapshot.change.Origin}
 	history := inspection.Metadata().History(path)

internal/engine/inheritance_load.go

@@ -3,14 +3,28 @@ package engine
 import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 
 func containsInheritanceDirective(root *document.Node) bool {
-	found := false
+	var visit func(*document.Node) bool
-	walkDocument(root, Path{}, func(path Path, _ *document.Node) {
+	visit = func(node *document.Node) bool {
-		if len(path.segments) != 0 && path.segments[len(path.segments)-1].kind == pathSegmentKey &&
+		if node == nil {
-			path.segments[len(path.segments)-1].key == inheritanceKey {
+			return false
-			found = true
 		}
-	})
+		switch node.Kind {
-	return found
+		case document.Mapping:
+			for _, entry := range node.Mapping {
+				if entry.Key == inheritanceKey || visit(entry.Value) {
+					return true
+				}
+			}
+		case document.Sequence:
+			for _, child := range node.Sequence {
+				if visit(child) {
+					return true
+				}
+			}
+		}
+		return false
+	}
+	return visit(root)
 }
 
 func inheritanceVersionDiagnostic(rule *VersionRule, expanded *inheritanceScope) *Diagnostic {

internal/engine/inheritance_origin.go

@@ -2,6 +2,7 @@ package engine
 
 import (
 	"slices"
+	"strconv"
 
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 )
@@ -74,10 +75,44 @@ func copyInheritanceSubtree(target, incoming map[string]Origin, node *document.N
 	})
 }
 
+type inheritanceStepKey struct {
+	from      string
+	to        string
+	reference string
+	locations string
+}
+
+func inheritanceStepKeyForPaths(from, to, reference Path, locations []Location) inheritanceStepKey {
+	return inheritanceStepKey{
+		from: from.String(), to: to.String(), reference: reference.String(),
+		locations: inheritanceLocationsKey(locations),
+	}
+}
+
+func inheritanceLocationsKey(locations []Location) string {
+	encoded := strconv.AppendInt(nil, int64(len(locations)), 10)
+	encoded = append(encoded, ';')
+	for _, location := range locations {
+		encoded = strconv.AppendInt(encoded, int64(len(location.SourceID)), 10)
+		encoded = append(encoded, ':')
+		encoded = append(encoded, location.SourceID...)
+		encoded = append(encoded, ';')
+		encoded = strconv.AppendInt(encoded, int64(location.Line), 10)
+		encoded = append(encoded, ';')
+		encoded = strconv.AppendInt(encoded, int64(location.Column), 10)
+		encoded = append(encoded, ';')
+	}
+	return string(encoded)
+}
+
 // Materialize concrete steps only for an inspection record. The linked private
 // traces remain compact when one parent supplies many descendant values.
 func projectInheritanceSteps(origin Origin) []InheritanceStep {
 	steps := cloneInheritanceSteps(origin.Inheritance)
+	seen := make(map[inheritanceStepKey]struct{}, len(steps))
+	for _, step := range steps {
+		seen[inheritanceStepKeyForPaths(step.From, step.To, step.Reference, step.Locations)] = struct{}{}
+	}
 	for _, contributor := range origin.contributors {
 		var reverse []*inheritanceTrace
 		for link := contributor.trace; link != nil; link = link.previous {
@@ -91,17 +126,13 @@ func projectInheritanceSteps(origin Origin) []InheritanceStep {
 				continue
 			}
 			next := appendInheritancePath(transfer.to, relative)
-			step := InheritanceStep{
+			key := inheritanceStepKeyForPaths(current, next, transfer.reference, transfer.locations)
+			if _, found := seen[key]; !found {
+				seen[key] = struct{}{}
+				steps = append(steps, InheritanceStep{
 					From: current.clone(), To: next.clone(), Reference: transfer.reference.clone(),
 					Locations: cloneLocations(transfer.locations),
-			}
+				})
-			if !slices.ContainsFunc(steps, func(existing InheritanceStep) bool {
-				return existing.From.String() == step.From.String() &&
-					existing.To.String() == step.To.String() &&
-					existing.Reference.String() == step.Reference.String() &&
-					slices.Equal(existing.Locations, step.Locations)
-			}) {
-				steps = append(steps, step)
 			}
 			current = next
 		}

internal/engine/inheritance_origin_test.go

@@ -2,6 +2,8 @@ package engine
 
 import (
 	"io/fs"
+	"reflect"
+	"slices"
 	"testing"
 	"testing/fstest"
 
@@ -85,6 +87,165 @@ func TestInheritedOriginsKeepSourcePathsPresenceAndIndependentReplacement(t *tes
 	}
 }
 
+func TestOriginMembershipPreservesLocationAndSourceCoverageRules(t *testing.T) {
+	location := Location{SourceID: "source", Line: 4, Column: 2}
+	otherCoordinates := location
+	otherCoordinates.Line++
+
+	container := Origin{
+		Layer:     LayerOverlay,
+		Operation: ChangeNormalization,
+		Locations: []Location{location},
+	}
+	if !originContainedBy(container, container) {
+		t.Fatal("identical location evidence was not contained")
+	}
+	coordinateDifference := container
+	coordinateDifference.Locations = []Location{otherCoordinates}
+	if originContainedBy(coordinateDifference, container) {
+		t.Fatal("location containment ignored differing coordinates")
+	}
+
+	parent := Keys("parent")
+	child := parent.Key("child")
+	change := Change{Path: parent, Origin: container}
+	descendantOrigin := Origin{
+		Layer:     container.Layer,
+		Operation: container.Operation,
+		Locations: []Location{otherCoordinates},
+	}
+	if !originRepresentedByChange(child, descendantOrigin, change) {
+		t.Fatal("descendant source coverage rejected matching SourceID with different coordinates")
+	}
+	descendantOrigin.Locations[0].SourceID = "another-source"
+	if originRepresentedByChange(child, descendantOrigin, change) {
+		t.Fatal("descendant source coverage accepted an unrecorded SourceID")
+	}
+
+	withContributor := container
+	withContributor.contributors = []inheritanceContributor{{source: parent, location: location}}
+	if originContainedBy(withContributor, container) {
+		t.Fatal("exact location containment ignored the contributor-empty mismatch")
+	}
+	if !originRepresentedByChange(child, withContributor, change) {
+		t.Fatal("descendant source coverage was conflated with contributor containment")
+	}
+}
+
+func TestProjectedInheritanceStepsMatchScanAndRetainOwnership(t *testing.T) {
+	sourcePath := Keys("source", "a/b", "01")
+	firstLocations := []Location{{SourceID: "first;:source", Line: -1, Column: 2}}
+	secondLocations := []Location{
+		{SourceID: "second:;source", Line: 3, Column: -4},
+		{SourceID: "", Line: -5, Column: 6},
+	}
+	firstTransfer := inheritanceTransfer{
+		from: Keys("source"), to: Keys("middle"), reference: Keys("middle", "extends"), locations: firstLocations,
+	}
+	secondTransfer := inheritanceTransfer{
+		from: Keys("middle"), to: Keys("target"), reference: Keys("target", "extends"), locations: secondLocations,
+	}
+	firstTrace := &inheritanceTrace{transfer: &firstTransfer}
+	chain := &inheritanceTrace{previous: firstTrace, transfer: &secondTransfer}
+	firstStep := InheritanceStep{
+		From: sourcePath, To: Keys("middle", "a/b", "01"), Reference: firstTransfer.reference, Locations: firstLocations,
+	}
+
+	duplicateFirstTransfer := firstTransfer
+	duplicateSecondTransfer := secondTransfer
+	duplicateChain := &inheritanceTrace{
+		previous: &inheritanceTrace{transfer: &duplicateFirstTransfer},
+		transfer: &duplicateSecondTransfer,
+	}
+	reversedLocations := []Location{secondLocations[1], secondLocations[0]}
+	reorderedSecondTransfer := secondTransfer
+	reorderedSecondTransfer.locations = reversedLocations
+	reorderedChain := &inheritanceTrace{
+		previous: &inheritanceTrace{transfer: &duplicateFirstTransfer},
+		transfer: &reorderedSecondTransfer,
+	}
+	origin := Origin{
+		Inheritance: []InheritanceStep{firstStep, firstStep},
+		contributors: []inheritanceContributor{
+			{source: sourcePath, trace: chain},
+			{source: sourcePath, trace: duplicateChain},
+			{source: sourcePath, trace: reorderedChain},
+			{source: sourcePath, trace: chain},
+		},
+	}
+
+	want := projectInheritanceStepsByScan(origin)
+	got := projectInheritanceSteps(origin)
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("projected steps differ from ordered scan:\n got: %#v\nwant: %#v", got, want)
+	}
+	if len(got) != 4 || got[0].From.String() != "/source/a~1b/01" || got[0].To.String() != "/middle/a~1b/01" ||
+		!reflect.DeepEqual(got[0], got[1]) || got[2].To.String() != "/target/a~1b/01" ||
+		!reflect.DeepEqual(got[2].Locations, secondLocations) || !reflect.DeepEqual(got[3].Locations, reversedLocations) {
+		t.Fatalf("unexpected duplicate/order/escape projection: %#v", got)
+	}
+
+	got[0].From.segments[0].key = "mutated"
+	got[2].Locations[0].SourceID = "mutated"
+	if repeated := projectInheritanceSteps(origin); !reflect.DeepEqual(repeated, want) {
+		t.Fatalf("returned steps mutated retained evidence:\n got: %#v\nwant: %#v", repeated, want)
+	}
+}
+
+func TestInheritanceLocationsKeyEncodesOrderedLengthPrefixedValues(t *testing.T) {
+	if inheritanceLocationsKey(nil) != inheritanceLocationsKey([]Location{}) {
+		t.Fatal("nil and empty location lists should encode equally")
+	}
+	values := [][]Location{
+		{{SourceID: "a;1;-2;", Line: -3, Column: 4}},
+		{{SourceID: "a", Line: 1, Column: -2}, {SourceID: ";1;-2;", Line: -3, Column: 4}},
+		{{SourceID: ";1;-2;", Line: -3, Column: 4}, {SourceID: "a", Line: 1, Column: -2}},
+		{{SourceID: "é", Line: -3, Column: 4}},
+		{{SourceID: "e", Line: -3, Column: 4}},
+	}
+	keys := make(map[string]int, len(values))
+	for index, locations := range values {
+		key := inheritanceLocationsKey(locations)
+		if previous, found := keys[key]; found {
+			t.Fatalf("location lists %d and %d encoded identically", previous, index)
+		}
+		keys[key] = index
+	}
+}
+
+func projectInheritanceStepsByScan(origin Origin) []InheritanceStep {
+	steps := cloneInheritanceSteps(origin.Inheritance)
+	for _, contributor := range origin.contributors {
+		var reverse []*inheritanceTrace
+		for link := contributor.trace; link != nil; link = link.previous {
+			reverse = append(reverse, link)
+		}
+		current := contributor.source
+		for index := len(reverse) - 1; index >= 0; index-- {
+			transfer := reverse[index].transfer
+			relative, ok := relativeHistoryPath(transfer.from, current)
+			if !ok {
+				continue
+			}
+			next := appendInheritancePath(transfer.to, relative)
+			step := InheritanceStep{
+				From: current.clone(), To: next.clone(), Reference: transfer.reference.clone(),
+				Locations: cloneLocations(transfer.locations),
+			}
+			if !slices.ContainsFunc(steps, func(existing InheritanceStep) bool {
+				return existing.From.String() == step.From.String() &&
+					existing.To.String() == step.To.String() &&
+					existing.Reference.String() == step.Reference.String() &&
+					slices.Equal(existing.Locations, step.Locations)
+			}) {
+				steps = append(steps, step)
+			}
+			current = next
+		}
+	}
+	return steps
+}
+
 func TestInheritedOriginsRetainChainsAndNestedDestinations(t *testing.T) {
 	first := parseCompositionDocument(t, "source-1", `first:
   enabled: false

internal/engine/inheritance_test.go

@@ -121,6 +121,24 @@ func TestSiblingInheritanceRejectsInvalidRelationships(t *testing.T) {
 	}
 }
 
+func TestLoadDetectsInvalidInheritanceInsideSequence(t *testing.T) {
+	input := []byte(`items:
+  - child: {extends: true}
+`)
+	result, err := testLoad[map[string]any](Bytes("nested-inheritance.yml", input), Options[map[string]any]{})
+	if result != nil || err == nil {
+		t.Fatalf("result, err = %#v, %v; want invalid nested inheritance", result, err)
+	}
+	loadError, ok := err.(*LoadError)
+	if !ok {
+		t.Fatalf("error type = %T, want *LoadError", err)
+	}
+	diagnostics := loadError.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeInheritanceInvalid || diagnostics[0].Path.String() != "/items/0/child/extends" {
+		t.Fatalf("diagnostics = %#v", diagnostics)
+	}
+}
+
 func TestSiblingInheritanceDetectsDeepCycleWithoutRecursiveDependencyWalk(t *testing.T) {
 	const count = 2048
 	entries := make([]document.Entry, count)

internal/engine/load.go

@@ -84,7 +84,9 @@ type Inspection struct {
 	input            *document.Node
 	inputOrigins     map[string]Origin
 	final            *document.Node
+	immutableLookup  *documentLookup
 	resolution       []resolutionSnapshot
+	resolutionReplay []resolutionSnapshot
 	applications     []historyApplication
 	inheritance      []inheritanceOperation
 	secrets          map[string]bool

internal/engine/load_metadata.go

@@ -157,15 +157,12 @@ func originRepresentedByChange(path Path, origin Origin, change Change) bool {
 	// A subtree replacement already records its descendants' contributions.
 	// Their coordinates differ from the container's, but their sources must be
 	// covered by the operation; matching only the precedence role is insufficient.
-	for _, location := range origin.Locations {
+	recordedSources := make(map[string]struct{}, len(change.Origin.Locations))
-		found := false
 	for _, recorded := range change.Origin.Locations {
-			if location.SourceID == recorded.SourceID {
+		recordedSources[recorded.SourceID] = struct{}{}
-				found = true
-				break
 	}
-		}
+	for _, location := range origin.Locations {
-		if !found {
+		if _, found := recordedSources[location.SourceID]; !found {
 			return false
 		}
 	}
@@ -189,15 +186,12 @@ func originContainedBy(candidate, container Origin) bool {
 	if candidate.Layer != container.Layer || candidate.Operation != container.Operation {
 		return false
 	}
+	availableLocations := make(map[Location]struct{}, len(container.Locations))
+	for _, location := range container.Locations {
+		availableLocations[location] = struct{}{}
+	}
 	for _, location := range candidate.Locations {
-		found := false
+		if _, found := availableLocations[location]; !found {
-		for _, available := range container.Locations {
-			if location == available {
-				found = true
-				break
-			}
-		}
-		if !found {
 			return false
 		}
 	}
@@ -257,6 +251,7 @@ func cloneMetadata(metadata Metadata) Metadata {
 		fields:           make(map[string]FieldInfo, len(metadata.fields)),
 		history:          make(map[string][]Change, len(metadata.history)),
 		inheritance:      append([]inheritanceOperation(nil), metadata.inheritance...),
+		inheritanceIndex: metadata.inheritanceIndex,
 	}
 	cloned.effectivePaths = make(map[string]Path, len(metadata.effectivePaths))
 	for pointer, path := range metadata.effectivePaths {
@@ -280,8 +275,23 @@ func cloneMetadata(metadata Metadata) Metadata {
 }
 
 func applyResolutionMetadata(metadata *Metadata, resolved resolutionResult) {
-	for _, snapshot := range resolved.snapshots {
+	finalPaths := make(map[string]*document.Node)
-		pointer := snapshot.change.Path.String()
+	indexDocument(resolved.final, Path{}, finalPaths)
+	snapshotCoverage, snapshotPointers := newResolutionCoverageIndexFromSnapshots(resolved.snapshots)
+	var deltaCoverage pathPrefixIndex
+	snapshotIDs := make([]int, len(resolved.deltas))
+	for id, delta := range resolved.deltas {
+		if delta.path.valid() {
+			deltaCoverage.insert(delta.path.String(), id)
+		}
+		snapshotIDs[id] = -1
+		if snapshotID, ok := snapshotCoverage.deepestCoveringID(delta.path); ok {
+			snapshotIDs[id] = snapshotID
+		}
+	}
+
+	for snapshotID, snapshot := range resolved.snapshots {
+		pointer := snapshotPointers[snapshotID]
 		change := cloneChange(snapshot.change)
 		if info, ok := metadata.fields[pointer]; ok {
 			change.Previous = []Origin{cloneOrigin(info.Origin)}
@@ -290,52 +300,40 @@ func applyResolutionMetadata(metadata *Metadata, resolved resolutionResult) {
 		}
 		metadata.history[pointer] = append(metadata.history[pointer], change)
 	}
-	appendResolutionDescendantHistory(metadata, resolved)
+
-	for _, delta := range resolved.deltas {
+	appendResolutionDescendantHistory(metadata, resolved.snapshots, snapshotPointers, finalPaths, &deltaCoverage, snapshotIDs)
-		record := coveringResolutionSnapshot(resolved.snapshots, delta.path)
+	applyResolutionFieldOrigins(metadata.fields, resolved.snapshots, &deltaCoverage, snapshotIDs)
-		if record == nil {
+	refreshResolutionFields(metadata.fields, finalPaths, resolved.snapshots, snapshotCoverage)
-			continue
-		}
-		for pointer, info := range metadata.fields {
-			path, err := ParsePath(pointer)
-			if err != nil || !pathContains(delta.path, path) {
-				continue
-			}
-			info.Origin = cloneOrigin(record.change.Origin)
-			metadata.fields[pointer] = info
-		}
-	}
-	refreshResolutionFields(metadata.fields, resolved.final, resolved.snapshots)
 }
 
-func appendResolutionDescendantHistory(metadata *Metadata, resolved resolutionResult) {
+func appendResolutionDescendantHistory(metadata *Metadata, snapshots []resolutionSnapshot, snapshotPointers []string, finalPaths map[string]*document.Node, deltaIndex *pathPrefixIndex, snapshotIDs []int) {
-	finalPaths := make(map[string]*document.Node)
+	allPointers := make(map[string]struct{}, len(metadata.history)+len(finalPaths))
-	indexDocument(resolved.final, Path{}, finalPaths)
-	for _, delta := range resolved.deltas {
-		record := coveringResolutionSnapshot(resolved.snapshots, delta.path)
-		if record == nil {
-			continue
-		}
-		affected := make(map[string]bool)
 	for pointer := range metadata.history {
-			if path, err := ParsePath(pointer); err == nil && pathContains(delta.path, path) {
+		if _, err := ParsePath(pointer); err == nil {
-				affected[pointer] = true
+			allPointers[pointer] = struct{}{}
 		}
 	}
 	for pointer := range finalPaths {
-			if path, err := ParsePath(pointer); err == nil && pathContains(delta.path, path) {
+		allPointers[pointer] = struct{}{}
-				affected[pointer] = true
 	}
+	buckets := make([][]string, len(snapshotIDs))
+	for pointer := range allPointers {
+		deltaIndex.visitAncestors(pointer, func(deltaID int) {
+			snapshotID := snapshotIDs[deltaID]
+			if snapshotID < 0 || pointer == snapshotPointers[snapshotID] {
+				return
 			}
-		pointers := make([]string, 0, len(affected))
+			buckets[deltaID] = append(buckets[deltaID], pointer)
-		for pointer := range affected {
+		})
-			if pointer != record.change.Path.String() {
-				pointers = append(pointers, pointer)
 	}
+	for deltaID, pointers := range buckets {
+		snapshotID := snapshotIDs[deltaID]
+		if snapshotID < 0 {
+			continue
 		}
 		slices.Sort(pointers)
 		for _, pointer := range pointers {
-			change := cloneChange(record.change)
+			change := cloneChange(snapshots[snapshotID].change)
 			if info, ok := metadata.fields[pointer]; ok {
 				change.Previous = []Origin{cloneOrigin(info.Origin)}
 			}
@@ -344,20 +342,33 @@ func appendResolutionDescendantHistory(metadata *Metadata, resolved resolutionRe
 	}
 }
 
-func coveringResolutionSnapshot(snapshots []resolutionSnapshot, path Path) *resolutionSnapshot {
+func applyResolutionFieldOrigins(fields map[string]FieldInfo, snapshots []resolutionSnapshot, deltaIndex *pathPrefixIndex, snapshotIDs []int) {
-	var covering *resolutionSnapshot
+	buckets := make([][]string, len(snapshotIDs))
-	for index := range snapshots {
+	for pointer := range fields {
-		snapshot := &snapshots[index]
+		if _, err := ParsePath(pointer); err != nil {
-		if pathContains(snapshot.change.Path, path) && (covering == nil || len(snapshot.change.Path.segments) > len(covering.change.Path.segments)) {
+			continue
-			covering = snapshot
+		}
+		deltaIndex.visitAncestors(pointer, func(deltaID int) {
+			if snapshotIDs[deltaID] >= 0 {
+				buckets[deltaID] = append(buckets[deltaID], pointer)
+			}
+		})
+	}
+	for deltaID, pointers := range buckets {
+		snapshotID := snapshotIDs[deltaID]
+		if snapshotID < 0 {
+			continue
+		}
+		origin := snapshots[snapshotID].change.Origin
+		for _, pointer := range pointers {
+			info := fields[pointer]
+			info.Origin = cloneOrigin(origin)
+			fields[pointer] = info
 		}
 	}
-	return covering
 }
 
-func refreshResolutionFields(fields map[string]FieldInfo, final *document.Node, snapshots []resolutionSnapshot) {
+func refreshResolutionFields(fields map[string]FieldInfo, finalPaths map[string]*document.Node, snapshots []resolutionSnapshot, snapshotCoverage *resolutionCoverageIndex) {
-	finalPaths := make(map[string]*document.Node)
-	indexDocument(final, Path{}, finalPaths)
 	for pointer := range fields {
 		if _, ok := finalPaths[pointer]; !ok {
 			delete(fields, pointer)
@@ -370,10 +381,8 @@ func refreshResolutionFields(fields map[string]FieldInfo, final *document.Node,
 			continue
 		}
 		origin := Origin{Layer: LayerResolution}
-		if path, err := ParsePath(pointer); err == nil {
+		if snapshotID, ok := snapshotCoverage.deepestCoveringPointerID(pointer); ok {
-			if covering := coveringResolutionSnapshot(snapshots, path); covering != nil {
+			origin = cloneOrigin(snapshots[snapshotID].change.Origin)
-				origin = cloneOrigin(covering.change.Origin)
-			}
 		}
 		fields[pointer] = FieldInfo{Null: node.Kind == document.Null, Origin: origin}
 	}

internal/engine/load_result.go

@@ -98,6 +98,11 @@ 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)
+	retainedTrees := make([]*document.Node, 0, len(applications)+2)
+	retainedTrees = append(retainedTrees, decoded.final, final)
+	for _, application := range applications {
+		retainedTrees = append(retainedTrees, application.value)
+	}
 	inspection := &Inspection{
 		metadata:         metadata,
 		sources:          cloneSourceInfos(accumulator.sources),
@@ -107,7 +112,9 @@ func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T]
 		input:            decoded.final,
 		inputOrigins:     cloneOriginIndex(decoded.origins),
 		final:            final,
+		immutableLookup:  buildDocumentLookup(retainedTrees...),
 		resolution:       resolutionSnapshots,
+		resolutionReplay: coalescedResolutionSnapshots(resolutionSnapshots),
 		applications:     applications,
 		inheritance:      inheritanceOperations(resolved.inheritance),
 		secrets:          secrets,

internal/engine/metadata.go

@@ -14,15 +14,13 @@ type Metadata struct {
 	fields           map[string]FieldInfo
 	history          map[string][]Change
 	inheritance      []inheritanceOperation
+	inheritanceIndex *inheritanceHistoryIndex
 }
 
 // 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()]) {
+	info, ok := m.effectiveField(path)
-		return FieldInfo{}, false
-	}
-	info, ok := m.fields[path.String()]
 	if !ok {
 		return FieldInfo{}, false
 	}
@@ -34,10 +32,23 @@ func (m Metadata) Lookup(path Path) (FieldInfo, bool) {
 // IsExplicit reports whether a surviving input contribution, including one
 // inherited from a sibling, explicitly defined path.
 func (m Metadata) IsExplicit(path Path) bool {
-	info, ok := m.Lookup(path)
+	info, ok := m.effectiveField(path)
 	return ok && info.Explicit
 }
 
+func (m Metadata) effectiveField(path Path) (FieldInfo, bool) {
+	if !path.valid() {
+		return FieldInfo{}, false
+	}
+	pointer := path.String()
+	candidate, ok := m.effectivePaths[pointer]
+	if !ok || !matchesPathShape(path, candidate) {
+		return FieldInfo{}, false
+	}
+	info, ok := m.fields[pointer]
+	return info, ok
+}
+
 // History returns detached definition, inheritance, 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.
@@ -47,7 +58,11 @@ func (m Metadata) History(path Path) []Change {
 		return nil
 	}
 	history := m.history[path.String()]
-	return historyWithInheritance(path, history, m.inheritance)
+	operations := m.inheritance
+	if m.inheritanceIndex != nil {
+		operations = m.inheritanceIndex.matchingOperations(path, m.inheritance)
+	}
+	return historyWithInheritance(path, history, operations)
 }
 
 // HistoricalPaths returns the paths observed during loading, including effective
@@ -79,11 +94,14 @@ func (m Metadata) HistoricalPaths() []Path {
 // 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) {
+	if !query.valid() || len(query.segments) != len(candidate.segments) {
 		return false
 	}
 	for i, segment := range query.segments {
 		actual := candidate.segments[i]
+		if !pathTokenSpellingEqual(segment, actual) {
+			return false
+		}
 		if actual.kind == pathSegmentIndex {
 			index, ok := schemaIndex(segment)
 			if !ok || index != actual.index {
@@ -109,10 +127,9 @@ func (m Metadata) hasHistoricalPath(path Path) bool {
 }
 
 func finalizeMetadataPaths(m *Metadata, final *document.Node, applications []historyApplication, earlier ...*document.Node) {
-	m.effectivePaths = effectivePathIndex(final)
+	m.effectivePaths = make(map[string]Path)
 	m.historicalPaths = make(map[string][]Path)
-	add := func(path Path, _ *document.Node) {
+	addHistorical := func(path Path, pointer string) {
-		pointer := path.String()
 		for _, prior := range m.historicalPaths[pointer] {
 			if matchesPathShape(path, prior) {
 				return
@@ -120,7 +137,14 @@ func finalizeMetadataPaths(m *Metadata, final *document.Node, applications []his
 		}
 		m.historicalPaths[pointer] = append(m.historicalPaths[pointer], path.clone())
 	}
-	walkDocument(final, Path{}, add)
+	walkDocument(final, Path{}, func(path Path, _ *document.Node) {
+		pointer := path.String()
+		m.effectivePaths[pointer] = path.clone()
+		addHistorical(path, pointer)
+	})
+	add := func(path Path, _ *document.Node) {
+		addHistorical(path, path.String())
+	}
 	for _, tree := range earlier {
 		walkDocument(tree, Path{}, add)
 	}
@@ -142,6 +166,7 @@ func finalizeMetadataPaths(m *Metadata, final *document.Node, applications []his
 			walkDocument(operation.effective, operation.transfer.to, add)
 		}
 	}
+	m.inheritanceIndex = newInheritanceHistoryIndex(m.inheritance)
 }
 
 // effectivePathIndex records document-derived paths with their contextual segment

internal/engine/metadata_test.go

@@ -47,6 +47,60 @@ func TestMetadataHistoricalPaths(t *testing.T) {
 	}
 }
 
+func TestMetadataPathIndexesOwnIndependentSegments(t *testing.T) {
+	t.Parallel()
+
+	final := parseDocumentForDecode(t, "service: {workers: [1]}\n")
+	var metadata Metadata
+	finalizeMetadataPaths(&metadata, final, nil)
+	pointer := "/service/workers/0"
+	effective := metadata.effectivePaths[pointer]
+	historical := metadata.historicalPaths[pointer]
+	if effective.String() != pointer || len(historical) != 1 || historical[0].String() != pointer {
+		t.Fatalf("path indexes = %#v, %#v", effective, historical)
+	}
+
+	effective.segments[0].key = "effective"
+	if historical[0].String() != pointer {
+		t.Fatal("effective path mutation changed historical path")
+	}
+	historical[0].segments[2].index = 1
+	if effective.String() != "/effective/workers/0" {
+		t.Fatal("historical path mutation changed effective path")
+	}
+}
+
+func TestMetadataPathIndexesRetainDistinctHistoricalShapes(t *testing.T) {
+	t.Parallel()
+
+	final := parseDocumentForDecode(t, "shape: [replacement]\n")
+	earlier := parseDocumentForDecode(t, "shape: {'0': base}\n")
+	var metadata Metadata
+	// Repeated trees must not add duplicate shapes to the historical index.
+	finalizeMetadataPaths(&metadata, final, nil, earlier, earlier, final)
+	keyPath := Keys("shape", "0")
+	indexPath := Keys("shape").Index(0)
+	pointer := indexPath.String()
+	if !reflect.DeepEqual(metadata.effectivePaths[pointer], indexPath) {
+		t.Fatal("effective index does not reflect the final sequence")
+	}
+	historical := metadata.historicalPaths[pointer]
+	if len(historical) != 2 {
+		t.Fatalf("historical shapes = %#v, want one key and one index", historical)
+	}
+	for _, want := range []Path{keyPath, indexPath} {
+		found := false
+		for _, path := range historical {
+			if reflect.DeepEqual(path, want) {
+				found = true
+			}
+		}
+		if !found || !metadata.hasHistoricalPath(want) {
+			t.Fatalf("historical index lost shape %#v", want)
+		}
+	}
+}
+
 func TestHistoricalPathsExposeHiddenBaseOwnershipWithoutResolvingBaseSecrets(t *testing.T) {
 	t.Setenv("CONFIGKIT_HISTORY_UNUSED_PROD_KEY", "")
 	t.Setenv("CONFIGKIT_HISTORY_TEST_KEY", "synthetic-test-key")
@@ -231,6 +285,75 @@ func TestResolutionInputKeepsDetachedEntryMetadata(t *testing.T) {
 	}
 }
 
+func TestMetadataIsExplicitAgreesWithLookup(t *testing.T) {
+	t.Parallel()
+
+	type entry struct {
+		Kept    string `yaml:"kept"`
+		Set     string `yaml:"set"`
+		Enabled bool   `yaml:"enabled"`
+		Count   int    `yaml:"count"`
+	}
+	type config struct {
+		Nested   entry            `yaml:"nested"`
+		Nullable *string          `yaml:"nullable"`
+		Nodes    map[string]entry `yaml:"nodes"`
+	}
+
+	input := []byte(`nested: {set: configured, enabled: false, count: 0}
+nullable: null
+nodes:
+  base: {enabled: false, count: 0}
+  copy: {extends: base}
+`)
+	result, err := testLoad(Bytes("metadata-presence.yml", input), Options[config]{Definition: Definition[config]{
+		Defaults: func() config {
+			return config{
+				Nested: entry{Kept: "default", Set: "default", Enabled: true, Count: 7},
+				Nodes:  map[string]entry{"copy": {Kept: "node default"}},
+			}
+		},
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	metadata := result.Metadata()
+	tests := []struct {
+		name          string
+		path          Path
+		wantExplicit  bool
+		wantNull      bool
+		wantInherited bool
+	}{
+		{name: "default", path: Keys("nested", "kept")},
+		{name: "direct input", path: Keys("nested", "set"), wantExplicit: true},
+		{name: "explicit false", path: Keys("nested", "enabled"), wantExplicit: true},
+		{name: "explicit zero", path: Keys("nested", "count"), wantExplicit: true},
+		{name: "explicit null", path: Keys("nullable"), wantExplicit: true, wantNull: true},
+		{name: "inherited input", path: Keys("nodes", "copy", "enabled"), wantExplicit: true, wantInherited: true},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			info, found := metadata.Lookup(test.path)
+			if !found {
+				t.Fatalf("Lookup(%s) did not find an effective path", test.path)
+			}
+			if got := metadata.IsExplicit(test.path); got != info.Explicit || got != test.wantExplicit {
+				t.Fatalf("IsExplicit(%s) = %v, Lookup explicit = %v, want %v", test.path, got, info.Explicit, test.wantExplicit)
+			}
+			if info.Null != test.wantNull {
+				t.Fatalf("Lookup(%s).Null = %v, want %v", test.path, info.Null, test.wantNull)
+			}
+			if inherited := len(info.Origin.Inheritance) != 0; inherited != test.wantInherited {
+				t.Fatalf("Lookup(%s) inherited = %v, want %v", test.path, inherited, test.wantInherited)
+			}
+		})
+	}
+	if result.Config.Nested.Enabled || result.Config.Nested.Count != 0 || result.Config.Nullable != nil {
+		t.Fatalf("explicit values changed during loading: %#v", result.Config)
+	}
+}
+
 func TestQueriesRespectActualHistoricalAndEffectiveContainers(t *testing.T) {
 	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 {

internal/engine/overlay.go

@@ -131,9 +131,24 @@ func previousOrigins(origin Origin) []Origin {
 func displacedOrigins(node *document.Node, origins map[string]Origin, path Path) []displacedDefinition {
 	var displaced []displacedDefinition
 	collectDisplacedOrigins(&displaced, node, origins, path, Origin{})
-	slices.SortFunc(displaced, func(left, right displacedDefinition) int {
+	return sortDisplacedDefinitions(displaced)
-		return strings.Compare(left.path.String(), right.path.String())
+}
+
+func sortDisplacedDefinitions(displaced []displacedDefinition) []displacedDefinition {
+	type orderedDefinition struct {
+		definition displacedDefinition
+		pointer    string
+	}
+	ordered := make([]orderedDefinition, len(displaced))
+	for i, definition := range displaced {
+		ordered[i] = orderedDefinition{definition: definition, pointer: definition.path.String()}
+	}
+	slices.SortFunc(ordered, func(left, right orderedDefinition) int {
+		return strings.Compare(left.pointer, right.pointer)
 	})
+	for i, item := range ordered {
+		displaced[i] = item.definition
+	}
 	return displaced
 }
 

internal/engine/overlay_test.go

@@ -117,3 +117,26 @@ func TestOwnedOverlayKeepsCompositeContributorsAndAcquiredInputs(t *testing.T) {
 		t.Fatal("working tree mutation changed an acquired input")
 	}
 }
+
+func TestDisplacedOriginsSortEscapedPointers(t *testing.T) {
+	input := parseCompositionDocument(t, "source-1", `values:
+  z: old
+  a/b: slash
+  a~b: tilde
+  nested: {x: old}
+`)
+	composed, diagnostics := composeDocuments(input)
+	if len(diagnostics) != 0 {
+		t.Fatal(diagnostics)
+	}
+	displaced := displacedOrigins(composed.root, composed.origins, Path{})
+	want := []string{"", "/values", "/values/a~0b", "/values/a~1b", "/values/nested", "/values/nested/x", "/values/z"}
+	if len(displaced) != len(want) {
+		t.Fatalf("displaced definitions = %d, want %d", len(displaced), len(want))
+	}
+	for i, definition := range displaced {
+		if got := definition.path.String(); got != want[i] {
+			t.Fatalf("displaced[%d] path = %q, want %q", i, got, want[i])
+		}
+	}
+}

internal/engine/override.go

@@ -50,12 +50,16 @@ func prepareOverrides(base *composedDocument, sources []SourceInfo, overrides []
 	}
 
 	seen := make(map[string]int, len(overrides))
-	pathAccepted := make([]bool, len(overrides))
+	var acceptedPaths pathPrefixIndex
+	var baseLookup *documentLookup
+	if len(overrides) != 0 {
+		baseLookup = buildDocumentLookup(base.root)
+	}
 	var usedBytes int64
 	usedNodes := 0
 	for index, override := range overrides {
 		location := &Location{SourceID: prepared[index].source.ID}
-		if issue := validateOverridePath(override.Path, base.root); issue != nil {
+		if issue := validateOverridePath(override.Path, base.root, baseLookup); issue != nil {
 			issue.Primary = location
 			diagnostics = append(diagnostics, *issue)
 			continue
@@ -70,7 +74,7 @@ func prepareOverrides(base *composedDocument, sources []SourceInfo, overrides []
 			continue
 		}
 		seen[pointer] = index
-		if conflicting := overlappingOverride(overrides[:index], pathAccepted[:index], override.Path); conflicting >= 0 {
+		if conflicting, overlaps := acceptedPaths.earliestIntersectingID(pointer); overlaps {
 			diagnostics = append(diagnostics, Diagnostic{
 				Code: CodeOverrideOverlap, Severity: SeverityError, Path: override.Path.clone(),
 				Message: "configuration override paths overlap", Primary: location,
@@ -92,7 +96,7 @@ func prepareOverrides(base *composedDocument, sources []SourceInfo, overrides []
 			})
 			continue
 		}
-		pathAccepted[index] = true
+		acceptedPaths.insert(pointer, index)
 
 		builder := valueBuilder{sourceID: prepared[index].source.ID, active: make(map[valueVisit]bool)}
 		value, issue := builder.build(override.Value, override.Path, len(override.Path.segments))
@@ -150,7 +154,7 @@ func validOverrideLabel(label string) bool {
 	return true
 }
 
-func validateOverridePath(path Path, root *document.Node) *Diagnostic {
+func validateOverridePath(path Path, root *document.Node, lookup *documentLookup) *Diagnostic {
 	if !path.valid() || len(path.segments) == 0 {
 		return &Diagnostic{Code: CodeOverrideInvalidPath, Severity: SeverityError, Path: path.clone(), Message: "configuration override path must be a valid non-root mapping path"}
 	}
@@ -165,7 +169,7 @@ func validateOverridePath(path Path, root *document.Node) *Diagnostic {
 		if current.Kind != document.Mapping {
 			return &Diagnostic{Code: CodeOverrideInvalidPath, Severity: SeverityError, Path: path.clone(), Message: "configuration override path traverses a non-mapping value"}
 		}
-		position := documentEntryIndex(current.Mapping, segment.key)
+		position := lookup.find(current, segment.key)
 		if index == len(path.segments)-1 {
 			continue
 		}
@@ -178,15 +182,6 @@ func validateOverridePath(path Path, root *document.Node) *Diagnostic {
 	return nil
 }
 
-func overlappingOverride(previous []Override, valid []bool, path Path) int {
-	for index, override := range previous {
-		if valid[index] && (pathContains(override.Path, path) || pathContains(path, override.Path)) {
-			return index
-		}
-	}
-	return -1
-}
-
 func pathContainsDirective(path Path) bool {
 	for _, segment := range path.segments {
 		if segment.key == directiveKey {

internal/engine/override_apply.go

@@ -1,9 +1,6 @@
 package engine
 
 import (
-	"slices"
-	"strings"
-
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 )
 
@@ -86,8 +83,17 @@ func applyPreparedOverride(result *composedDocument, override preparedOverride,
 }
 
 func affectedOverrideOrigins(existing, incoming *document.Node, origins map[string]Origin, path Path, index *mappingIndex) []displacedDefinition {
-	displaced := []displacedDefinition{{path: path.clone(), origin: cloneOrigin(origins[path.String()])}}
+	var displaced []displacedDefinition
-	if existing.Kind == document.Mapping && incoming.Kind == document.Mapping {
+	collectAffectedOverrideOrigins(&displaced, existing, incoming, origins, path, index)
+	return sortDisplacedDefinitions(displaced)
+}
+
+func collectAffectedOverrideOrigins(displaced *[]displacedDefinition, existing, incoming *document.Node, origins map[string]Origin, path Path, index *mappingIndex) {
+	if existing.Kind != document.Mapping || incoming.Kind != document.Mapping {
+		collectDisplacedOrigins(displaced, existing, origins, path, Origin{})
+		return
+	}
+	*displaced = append(*displaced, displacedDefinition{path: path.clone(), origin: cloneOrigin(origins[path.String()])})
 	for _, entry := range incoming.Mapping {
 		position := index.find(existing, entry.Key)
 		if position < 0 {
@@ -96,16 +102,9 @@ func affectedOverrideOrigins(existing, incoming *document.Node, origins map[stri
 		childPath := path.Key(entry.Key)
 		childExisting := existing.Mapping[position].Value
 		if childExisting.Kind == document.Mapping && entry.Value.Kind == document.Mapping {
-				displaced = append(displaced, affectedOverrideOrigins(childExisting, entry.Value, origins, childPath, index)...)
+			collectAffectedOverrideOrigins(displaced, childExisting, entry.Value, origins, childPath, index)
 		} else {
-				displaced = append(displaced, displacedOrigins(childExisting, origins, childPath)...)
+			collectDisplacedOrigins(displaced, childExisting, origins, childPath, Origin{})
 		}
 	}
-	} else {
-		displaced = displacedOrigins(existing, origins, path)
-	}
-	slices.SortFunc(displaced, func(left, right displacedDefinition) int {
-		return strings.Compare(left.path.String(), right.path.String())
-	})
-	return displaced
 }

internal/engine/override_test.go

@@ -206,6 +206,132 @@ func TestOverrideValidationRejectsPathsOverlapValuesAndProtectedTargets(t *testi
 	}
 }
 
+func TestOverrideOverlapIndexPreservesFirstAcceptedSource(t *testing.T) {
+	type config struct {
+		Nested map[string]any `yaml:"nested"`
+	}
+	base := Bytes("override-overlap.yml", []byte("nested: {}\n"))
+	_, err := testLoad(base, Options[config]{Overrides: []Override{
+		{Path: Keys("nested"), Value: map[string]any{}, Flag: "--nested"},
+		{Path: Keys("nested", "first"), Value: "one", Flag: "--first"},
+		{Path: Keys("nested", "second"), Value: "two", Flag: "--second"},
+	}})
+	if err == nil {
+		t.Fatal("load succeeded with overlapping overrides")
+	}
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("error = %T %v, want *LoadError", err, err)
+	}
+	diagnostics := loadErr.Diagnostics()
+	var conflicts []Diagnostic
+	for _, diagnostic := range diagnostics {
+		if diagnostic.Code == CodeOverrideOverlap {
+			conflicts = append(conflicts, diagnostic)
+		}
+	}
+	if len(conflicts) != 2 {
+		t.Fatalf("overlap diagnostics = %#v, want two conflicts", diagnostics)
+	}
+	for index, path := range []string{"/nested/first", "/nested/second"} {
+		if conflicts[index].Path.String() != path || len(conflicts[index].Related) != 1 || conflicts[index].Related[0].SourceID != "source-2" {
+			t.Fatalf("conflict[%d] = %#v, want path %q related to first CLI source", index, conflicts[index], path)
+		}
+	}
+}
+
+func TestOverrideOverlapIndexIncludesAcceptedPathWithInvalidValue(t *testing.T) {
+	type config struct {
+		Nested map[string]any `yaml:"nested"`
+	}
+	base := Bytes("override-value-overlap.yml", []byte("nested: {}\n"))
+	_, err := testLoad(base, Options[config]{Overrides: []Override{
+		{Path: Keys("nested"), Value: time.Second, Flag: "--nested"},
+		{Path: Keys("nested", "child"), Value: "value", Flag: "--child"},
+	}})
+	if err == nil {
+		t.Fatal("load succeeded with an invalid value and overlapping path")
+	}
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("error = %T %v, want *LoadError", err, err)
+	}
+	var invalidValue, overlap bool
+	for _, diagnostic := range loadErr.Diagnostics() {
+		switch diagnostic.Code {
+		case CodeOverrideInvalidValue:
+			invalidValue = diagnostic.Path.String() == "/nested"
+		case CodeOverrideOverlap:
+			overlap = diagnostic.Path.String() == "/nested/child" && len(diagnostic.Related) == 1 && diagnostic.Related[0].SourceID == "source-2"
+		}
+	}
+	if !invalidValue || !overlap {
+		t.Fatalf("diagnostics = %#v, want invalid parent value and child overlap related to its source", loadErr.Diagnostics())
+	}
+}
+
+func TestRejectedOverridePathDoesNotCauseOverlap(t *testing.T) {
+	type config struct {
+		Scalar string `yaml:"scalar"`
+	}
+	base := Bytes("override-rejected-overlap.yml", []byte("scalar: value\n"))
+	_, err := testLoad(base, Options[config]{Overrides: []Override{
+		{Path: Keys("scalar", "child"), Value: "invalid", Flag: "--child"},
+		{Path: Keys("scalar"), Value: "valid", Flag: "--scalar"},
+	}})
+	if err == nil {
+		t.Fatal("load succeeded with a path traversing a scalar")
+	}
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("error = %T %v, want *LoadError", err, err)
+	}
+	diagnostics := loadErr.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideInvalidPath || diagnostics[0].Path.String() != "/scalar/child" {
+		t.Fatalf("diagnostics = %#v, want only the invalid descendant path", diagnostics)
+	}
+}
+
+func TestVersionRejectedOverridePathDoesNotCauseOverlap(t *testing.T) {
+	type config struct {
+		Nested map[string]any `yaml:"nested"`
+	}
+	base := Bytes("override-version-overlap.yml", []byte("nested: {}\n"))
+	version := &VersionRule{Path: Keys("nested", "locked"), Check: func(Version, *Validation) error { return nil }}
+	_, err := testLoad(base, Options[config]{
+		Definition: Definition[config]{Version: version},
+		Overrides: []Override{
+			{Path: Keys("nested"), Value: map[string]any{}, Flag: "--nested"},
+			{Path: Keys("nested", "other"), Value: "allowed", Flag: "--other"},
+		},
+	})
+	if err == nil {
+		t.Fatal("load succeeded despite an override of a schema-version ancestor")
+	}
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("error = %T %v, want *LoadError", err, err)
+	}
+	diagnostics := loadErr.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideVersion || diagnostics[0].Path.String() != "/nested" {
+		t.Fatalf("diagnostics = %#v, want only the protected ancestor path", diagnostics)
+	}
+}
+
+func TestEscapedOverrideKeysStayDistinctFromMultipleSegments(t *testing.T) {
+	type config struct {
+		Nested map[string]any `yaml:"nested"`
+	}
+	base := Bytes("override-escaped-keys.yml", []byte("nested: {}\n"))
+	_, err := testLoad(base, Options[config]{Overrides: []Override{
+		{Path: Keys("nested", "a/b"), Value: "single key", Flag: "--single"},
+		{Path: Keys("nested", "a", "b"), Value: "nested key", Flag: "--nested"},
+	}})
+	if err != nil {
+		t.Fatalf("load rejected distinct escaped path tokens: %v", err)
+	}
+}
+
 func TestOverrideCannotReplaceSchemaVersionAncestor(t *testing.T) {
 	type schemaConfig struct {
 		Version string `yaml:"version"`
@@ -271,6 +397,43 @@ func TestOverrideEqualReplacementStillAppearsInHistory(t *testing.T) {
 	}
 }
 
+func TestAffectedOverrideOriginsSortEscapedPointers(t *testing.T) {
+	existingInput := parseCompositionDocument(t, "source-1", `values:
+  z: old
+  a/b: slash
+  a~b: tilde
+  nested: {x: old}
+`)
+	existing, diagnostics := composeDocuments(existingInput)
+	if len(diagnostics) != 0 {
+		t.Fatal(diagnostics)
+	}
+	incoming := parseCompositionDocument(t, "source-2", `values:
+  z: new
+  a/b: new
+  a~b: new
+  nested: {x: new}
+`)
+	existingValues, ok := documentAtPath(existing.root, Keys("values"))
+	if !ok {
+		t.Fatal("existing values mapping is missing")
+	}
+	incomingValues, ok := documentAtPath(incoming, Keys("values"))
+	if !ok {
+		t.Fatal("incoming values mapping is missing")
+	}
+	displaced := affectedOverrideOrigins(existingValues, incomingValues, existing.origins, Keys("values"), &mappingIndex{})
+	want := []string{"/values", "/values/a~0b", "/values/a~1b", "/values/nested", "/values/nested/x", "/values/z"}
+	if len(displaced) != len(want) {
+		t.Fatalf("displaced definitions = %d, want %d", len(displaced), len(want))
+	}
+	for i, definition := range displaced {
+		if got := definition.path.String(); got != want[i] {
+			t.Fatalf("displaced[%d] path = %q, want %q", i, got, want[i])
+		}
+	}
+}
+
 func TestOverrideAggregateLimitsFailBeforeApplication(t *testing.T) {
 	base, diagnostics := composeDocuments(&document.Node{Kind: document.Mapping})
 	if len(diagnostics) != 0 {

internal/engine/path.go

@@ -86,7 +86,20 @@ func (p Path) String() string {
 		return ""
 	}
 
+	// Include each separator and the extra byte introduced by escaping a token.
+	// Use stack storage for sizing indexes without allocating another string.
+	size := len(p.segments)
+	var indexText [20]byte
+	for _, segment := range p.segments {
+		if segment.kind == pathSegmentIndex {
+			size += len(strconv.AppendInt(indexText[:0], int64(segment.index), 10))
+		} else {
+			size += len(segment.key) + strings.Count(segment.key, "~") + strings.Count(segment.key, "/")
+		}
+	}
+
 	var b strings.Builder
+	b.Grow(size)
 	for _, segment := range p.segments {
 		b.WriteByte('/')
 		if segment.kind == pathSegmentIndex {
@@ -115,6 +128,33 @@ func clonePathSegments(segments []pathSegment, extra int) []pathSegment {
 	return cloned
 }
 
+func pathTokenSpellingEqual(left, right pathSegment) bool {
+	switch {
+	case left.kind == pathSegmentIndex && right.kind == pathSegmentIndex:
+		return left.index == right.index
+	case left.kind == pathSegmentIndex:
+		return pathIndexSpellingEqual(left.index, right.key)
+	case right.kind == pathSegmentIndex:
+		return pathIndexSpellingEqual(right.index, left.key)
+	default:
+		return left.key == right.key
+	}
+}
+
+func pathIndexSpellingEqual(index int, token string) bool {
+	var scratch [20]byte
+	spelling := strconv.AppendInt(scratch[:0], int64(index), 10)
+	if len(spelling) != len(token) {
+		return false
+	}
+	for i, character := range spelling {
+		if character != token[i] {
+			return false
+		}
+	}
+	return true
+}
+
 func escapePathToken(token string) string {
 	token = strings.ReplaceAll(token, "~", "~0")
 	return strings.ReplaceAll(token, "/", "~1")

internal/engine/path_prefix.go

@@ -0,0 +1,138 @@
+package engine
+
+type pathPrefixIndex struct {
+	root pathPrefixNode
+}
+
+type pathPrefixNode struct {
+	children   map[string]*pathPrefixNode
+	ids        []int
+	minimumID  int
+	hasMinimum bool
+}
+
+func (node *pathPrefixNode) includeID(id int) {
+	if !node.hasMinimum || id < node.minimumID {
+		node.minimumID = id
+		node.hasMinimum = true
+	}
+}
+
+func (index *pathPrefixIndex) insert(pointer string, id int) {
+	node := &index.root
+	node.includeID(id)
+	visitCanonicalPointerTokens(pointer, func(token string) bool {
+		if node.children == nil {
+			node.children = make(map[string]*pathPrefixNode)
+		}
+		child := node.children[token]
+		if child == nil {
+			child = &pathPrefixNode{}
+			node.children[token] = child
+		}
+		node = child
+		node.includeID(id)
+		return true
+	})
+	node.ids = append(node.ids, id)
+}
+
+func (index *pathPrefixIndex) visitAncestors(pointer string, visit func(int)) {
+	node := &index.root
+	for _, id := range node.ids {
+		visit(id)
+	}
+	visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		for _, id := range node.ids {
+			visit(id)
+		}
+		return true
+	})
+}
+
+func (index *pathPrefixIndex) visitDescendants(pointer string, visit func(int)) {
+	root := index.nodeAt(pointer)
+	if root == nil {
+		return
+	}
+	var walk func(*pathPrefixNode)
+	walk = func(node *pathPrefixNode) {
+		for _, id := range node.ids {
+			visit(id)
+		}
+		for _, child := range node.children {
+			walk(child)
+		}
+	}
+	walk(root)
+}
+
+func (index *pathPrefixIndex) earliestIntersectingID(pointer string) (int, bool) {
+	bestID, found := 0, false
+	consider := func(id int) {
+		if !found || id < bestID {
+			bestID = id
+			found = true
+		}
+	}
+	node := &index.root
+	for _, id := range node.ids {
+		consider(id)
+	}
+	complete := visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		for _, id := range node.ids {
+			consider(id)
+		}
+		return true
+	})
+	if complete && node.hasMinimum {
+		consider(node.minimumID)
+	}
+	return bestID, found
+}
+
+func (index *pathPrefixIndex) nodeAt(pointer string) *pathPrefixNode {
+	node := &index.root
+	complete := visitCanonicalPointerTokens(pointer, func(token string) bool {
+		child := node.children[token]
+		if child == nil {
+			return false
+		}
+		node = child
+		return true
+	})
+	if !complete {
+		return nil
+	}
+	return node
+}
+
+func visitCanonicalPointerTokens(pointer string, visit func(string) bool) bool {
+	if pointer == "" {
+		return true
+	}
+	start := 1
+	for {
+		end := start
+		for end < len(pointer) && pointer[end] != '/' {
+			end++
+		}
+		if !visit(pointer[start:end]) {
+			return false
+		}
+		if end == len(pointer) {
+			return true
+		}
+		start = end + 1
+	}
+}

internal/engine/path_prefix_test.go

@@ -0,0 +1,81 @@
+package engine
+
+import (
+	"slices"
+	"strings"
+	"testing"
+)
+
+func TestPathPrefixIndexMatchesPointerScans(t *testing.T) {
+	entries := []struct {
+		pointer string
+		id      int
+	}{
+		{pointer: "", id: 12},
+		{pointer: "/", id: 9},
+		{pointer: "/a", id: 6},
+		{pointer: "/a", id: 2},
+		{pointer: "/a/b", id: 4},
+		{pointer: "/a/b/c", id: 0},
+		{pointer: "/a/bc", id: 10},
+		{pointer: "/a~1b", id: 3},
+		{pointer: "/a~0b", id: 1},
+		{pointer: "/a~01b", id: 5},
+		{pointer: "/items/0", id: 8},
+		{pointer: "/items/01", id: 7},
+		{pointer: "/items/+1", id: 11},
+	}
+	var index pathPrefixIndex
+	for _, entry := range entries {
+		index.insert(entry.pointer, entry.id)
+	}
+	queries := []string{
+		"", "/", "/a", "/a/b", "/a/b/c", "/a/b/c/d", "/a/bc", "/a/bc/d",
+		"/a~1b", "/a~0b", "/a~01b", "/items", "/items/0", "/items/01", "/items/1", "/missing",
+	}
+	for _, query := range queries {
+		gotAncestors := make([]int, 0)
+		index.visitAncestors(query, func(id int) { gotAncestors = append(gotAncestors, id) })
+		wantAncestors := make([]int, 0)
+		gotDescendants := make([]int, 0)
+		wantDescendants := make([]int, 0)
+		wantEarliest, foundEarliest := 0, false
+		for _, entry := range entries {
+			if pointerContainsByString(entry.pointer, query) {
+				wantAncestors = append(wantAncestors, entry.id)
+			}
+			if pointerContainsByString(query, entry.pointer) {
+				wantDescendants = append(wantDescendants, entry.id)
+			}
+			if pointerContainsByString(entry.pointer, query) || pointerContainsByString(query, entry.pointer) {
+				if !foundEarliest || entry.id < wantEarliest {
+					wantEarliest, foundEarliest = entry.id, true
+				}
+			}
+		}
+		index.visitDescendants(query, func(id int) { gotDescendants = append(gotDescendants, id) })
+		if !slices.Equal(sortedPrefixIDs(gotAncestors), sortedPrefixIDs(wantAncestors)) {
+			t.Errorf("ancestors(%q) = %v, want %v", query, sortedPrefixIDs(gotAncestors), sortedPrefixIDs(wantAncestors))
+		}
+		if !slices.Equal(sortedPrefixIDs(gotDescendants), sortedPrefixIDs(wantDescendants)) {
+			t.Errorf("descendants(%q) = %v, want %v", query, sortedPrefixIDs(gotDescendants), sortedPrefixIDs(wantDescendants))
+		}
+		gotEarliest, gotFound := index.earliestIntersectingID(query)
+		if gotEarliest != wantEarliest || gotFound != foundEarliest {
+			t.Errorf("earliestIntersectingID(%q) = %d, %v, want %d, %v", query, gotEarliest, gotFound, wantEarliest, foundEarliest)
+		}
+	}
+}
+
+func pointerContainsByString(container, descendant string) bool {
+	if container == "" {
+		return true
+	}
+	return descendant == container || strings.HasPrefix(descendant, container+"/")
+}
+
+func sortedPrefixIDs(ids []int) []int {
+	result := slices.Clone(ids)
+	slices.Sort(result)
+	return result
+}

internal/engine/path_test.go

@@ -1,6 +1,9 @@
 package engine
 
-import "testing"
+import (
+	"strconv"
+	"testing"
+)
 
 func TestPathRoundTripsSemanticKeys(t *testing.T) {
 	t.Parallel()
@@ -36,6 +39,73 @@ func TestPathRoundTripsSemanticKeys(t *testing.T) {
 	if got := Keys("items").Index(12).Key("name").String(); got != "/items/12/name" {
 		t.Fatalf("indexed path = %q", got)
 	}
+	maximum := int(^uint(0) >> 1)
+	for _, index := range []int{100, maximum, -1, -maximum - 1} {
+		want := "/items/" + strconv.Itoa(index)
+		if got := Keys("items").Index(index).String(); got != want {
+			t.Fatalf("indexed path = %q, want %q", got, want)
+		}
+	}
+}
+
+func TestPathContainmentMatchesPointerSpelling(t *testing.T) {
+	parse := func(pointer string) Path {
+		path, err := ParsePath(pointer)
+		if err != nil {
+			t.Fatalf("ParsePath(%q) error = %v", pointer, err)
+		}
+		return path
+	}
+	maximum := int(^uint(0) >> 1)
+	minimum := -maximum - 1
+	paths := []Path{
+		{},
+		Keys(""),
+		Keys("a"),
+		Keys("ab"),
+		Keys("a", "b"),
+		Keys("a/b"),
+		Keys("a~1b"),
+		Keys("~"),
+		Keys("0"),
+		Keys("01"),
+		Keys("+1"),
+		Keys("items").Index(0),
+		Keys("items").Index(maximum),
+		Keys("items").Index(minimum),
+		parse("/"),
+		parse("/a~1b"),
+		parse("/a~01b"),
+		parse("/~0"),
+		parse("/0"),
+		parse("/01"),
+		parse("/+1"),
+		parse("/items/0"),
+		parse("/items/" + strconv.Itoa(maximum)),
+		parse("/items/" + strconv.Itoa(minimum)),
+		Path{}.Index(-1),
+	}
+	for _, container := range paths {
+		for _, descendant := range paths {
+			got := pathContains(container, descendant)
+			want := pathContainsByPointer(container, descendant)
+			if got != want {
+				t.Errorf("pathContains(%q, %q) = %v, want %v", container.String(), descendant.String(), got, want)
+			}
+		}
+	}
+}
+
+func pathContainsByPointer(container, descendant Path) bool {
+	if !container.valid() || !descendant.valid() || len(container.segments) > len(descendant.segments) {
+		return false
+	}
+	prefix := container.String()
+	if prefix == "" {
+		return true
+	}
+	value := descendant.String()
+	return value == prefix || len(value) > len(prefix) && value[:len(prefix)] == prefix && value[len(prefix)] == '/'
 }
 
 func TestPathPreservesSegmentIntentAndImmutability(t *testing.T) {

internal/engine/projection_test.go

@@ -357,6 +357,21 @@ func TestCompareDocumentTreesTracksSemanticChanges(t *testing.T) {
 	}
 }
 
+func TestCompareConfigurationValuesSortEscapedPointers(t *testing.T) {
+	before := parseCompositionDocument(t, "before", `values: {z: old, 'a/b': old, 'a~b': old, nested: {x: old}}`)
+	after := parseCompositionDocument(t, "after", `values: {z: new, 'a/b': new, 'a~b': new, nested: {x: new}}`)
+	deltas := compareConfigurationValues(before, after)
+	want := []string{"/values/a~0b", "/values/a~1b", "/values/nested/x", "/values/z"}
+	if len(deltas) != len(want) {
+		t.Fatalf("deltas = %#v", deltas)
+	}
+	for i, delta := range deltas {
+		if got := delta.path.String(); got != want[i] {
+			t.Fatalf("delta[%d] path = %q, want %q", i, got, want[i])
+		}
+	}
+}
+
 func mustSchemaFor[T any](t *testing.T) *schemaDescriptor {
 	t.Helper()
 	schema, issue := testBuildSchema(reflect.TypeFor[T]())

internal/engine/resolution.go

@@ -26,6 +26,37 @@ type resolutionRecord struct {
 	reasons        []string
 	dependencies   []Path
 	helperExpected *document.Node
+	reasonSet      map[string]struct{}
+	dependencySet  map[string]struct{}
+}
+
+func (record *resolutionRecord) addReason(reason string) {
+	if record.reasonSet == nil {
+		record.reasonSet = make(map[string]struct{}, len(record.reasons)+1)
+		for _, existing := range record.reasons {
+			record.reasonSet[existing] = struct{}{}
+		}
+	}
+	if _, found := record.reasonSet[reason]; found {
+		return
+	}
+	record.reasonSet[reason] = struct{}{}
+	record.reasons = append(record.reasons, reason)
+}
+
+func (record *resolutionRecord) addDependency(path Path) {
+	pointer := path.String()
+	if record.dependencySet == nil {
+		record.dependencySet = make(map[string]struct{}, len(record.dependencies)+1)
+		for _, existing := range record.dependencies {
+			record.dependencySet[existing.String()] = struct{}{}
+		}
+	}
+	if _, found := record.dependencySet[pointer]; found {
+		return
+	}
+	record.dependencySet[pointer] = struct{}{}
+	record.dependencies = append(record.dependencies, path.clone())
 }
 
 type resolutionSnapshot struct {
@@ -207,9 +238,9 @@ func (state *resolutionState) addRecord(path Path, kind ChangeKind, reason strin
 	if kind == ChangeNormalization {
 		record.kind = ChangeNormalization
 	}
-	record.reasons = appendUniqueString(record.reasons, reason)
+	record.addReason(reason)
 	for _, dependency := range dependencies {
-		record.dependencies = appendUniquePath(record.dependencies, dependency)
+		record.addDependency(dependency)
 	}
 	if expected != nil {
 		record.helperExpected = document.Clone(expected)
@@ -272,14 +303,17 @@ func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error
 	}
 	deltas := compareConfigurationValues(decoded.final, after)
 	ordered := orderedResolutionRecords(state.records)
+	coverage := newResolutionCoverageIndexFromRecords(ordered)
+	beforeLookup := buildDocumentLookup(decoded.final)
+	afterLookup := buildDocumentLookup(after)
 	for _, delta := range deltas {
-		if coveringResolutionRecord(ordered, delta.path) == nil {
+		if _, ok := coverage.deepestCoveringID(delta.path); !ok {
 			state.addDiagnostic(CodeResolveUnrecordedChange, delta.path, "application resolution changed a value without a covering record")
 		}
 	}
 	for _, record := range ordered {
-		_, beforePresent := documentAtPath(decoded.final, record.path)
+		_, beforePresent := documentAtPathWithLookup(decoded.final, record.path, beforeLookup)
-		afterNode, afterPresent := documentAtPath(after, record.path)
+		afterNode, afterPresent := documentAtPathWithLookup(after, record.path, afterLookup)
 		if !beforePresent && !afterPresent {
 			state.addDiagnostic(CodeResolveInvalidRecord, record.path, "resolution record does not identify an existing or removed value")
 			continue
@@ -294,8 +328,8 @@ func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error
 
 	snapshots := make([]resolutionSnapshot, 0, len(ordered))
 	for _, record := range ordered {
-		beforeNode, _ := documentAtPath(decoded.final, record.path)
+		beforeNode, _ := documentAtPathWithLookup(decoded.final, record.path, beforeLookup)
-		afterNode, _ := documentAtPath(after, record.path)
+		afterNode, _ := documentAtPathWithLookup(after, record.path, afterLookup)
 		snapshots = append(snapshots, resolutionSnapshot{
 			change: Change{
 				Path:         record.path.clone(),
@@ -313,52 +347,82 @@ func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error
 }
 
 func orderedResolutionRecords(records map[string]*resolutionRecord) []*resolutionRecord {
-	ordered := make([]*resolutionRecord, 0, len(records))
+	type orderedRecord struct {
-	for _, record := range records {
+		record  *resolutionRecord
-		ordered = append(ordered, record)
+		pointer string
 	}
-	slices.SortFunc(ordered, func(left, right *resolutionRecord) int {
+	ordered := make([]orderedRecord, 0, len(records))
-		return strings.Compare(left.path.String(), right.path.String())
+	for _, record := range records {
+		ordered = append(ordered, orderedRecord{record: record, pointer: record.path.String()})
+	}
+	slices.SortFunc(ordered, func(left, right orderedRecord) int {
+		return strings.Compare(left.pointer, right.pointer)
 	})
-	return ordered
+	result := make([]*resolutionRecord, len(ordered))
+	for i, item := range ordered {
+		result[i] = item.record
+	}
+	return result
 }
 
-func coveringResolutionRecord(records []*resolutionRecord, path Path) *resolutionRecord {
+type resolutionCoverageIndex struct {
-	var covering *resolutionRecord
+	prefix pathPrefixIndex
-	for _, record := range records {
+	depths []int
-		if pathContains(record.path, path) && (covering == nil || len(record.path.segments) > len(covering.path.segments)) {
+}
-			covering = record
+
+func newResolutionCoverageIndexFromRecords(records []*resolutionRecord) *resolutionCoverageIndex {
+	index := &resolutionCoverageIndex{depths: make([]int, len(records))}
+	for id, record := range records {
+		index.depths[id] = len(record.path.segments)
+		if record.path.valid() {
+			index.prefix.insert(record.path.String(), id)
 		}
 	}
-	return covering
+	return index
+}
+
+func newResolutionCoverageIndexFromSnapshots(snapshots []resolutionSnapshot) (*resolutionCoverageIndex, []string) {
+	index := &resolutionCoverageIndex{depths: make([]int, len(snapshots))}
+	pointers := make([]string, len(snapshots))
+	for id, snapshot := range snapshots {
+		path := snapshot.change.Path
+		index.depths[id] = len(path.segments)
+		pointers[id] = path.String()
+		if path.valid() {
+			index.prefix.insert(pointers[id], id)
+		}
+	}
+	return index, pointers
+}
+
+func (index *resolutionCoverageIndex) deepestCoveringID(path Path) (int, bool) {
+	if !path.valid() {
+		return 0, false
+	}
+	return index.deepestCoveringPointerID(path.String())
+}
+
+func (index *resolutionCoverageIndex) deepestCoveringPointerID(pointer string) (int, bool) {
+	bestID, bestDepth, found := 0, -1, false
+	index.prefix.visitAncestors(pointer, func(id int) {
+		depth := index.depths[id]
+		if !found || depth > bestDepth || (depth == bestDepth && id < bestID) {
+			bestID, bestDepth, found = id, depth, true
+		}
+	})
+	return bestID, found
 }
 
 func pathContains(container, descendant Path) bool {
 	if !container.valid() || !descendant.valid() || len(container.segments) > len(descendant.segments) {
 		return false
 	}
-	if container.String() == "" {
+	for i, segment := range container.segments {
+		if !pathTokenSpellingEqual(segment, descendant.segments[i]) {
+			return false
+		}
+	}
 	return true
-	}
-	prefix := container.String()
-	value := descendant.String()
-	return value == prefix || strings.HasPrefix(value, prefix+"/")
-}
-
-func appendUniqueString(values []string, value string) []string {
-	if !slices.Contains(values, value) {
-		return append(values, value)
-	}
-	return values
-}
-
-func appendUniquePath(paths []Path, path Path) []Path {
-	for _, existing := range paths {
-		if existing.String() == path.String() {
-			return paths
-		}
-	}
-	return append(paths, path.clone())
 }
 
 func clonePaths(paths []Path) []Path {

internal/engine/resolution_index_test.go

@@ -0,0 +1,247 @@
+package engine
+
+import (
+	"reflect"
+	"slices"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestCoalescedResolutionSnapshotsMatchOrderedScan(t *testing.T) {
+	parsedDependency := parseOverrideTestPath(t, "/dependencies/item")
+	snapshots := []resolutionSnapshot{
+		{change: Change{Path: Keys("a", "b"), Reasons: []string{"child", "shared", "child"}, Dependencies: []Path{Keys("dependencies", "item")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "c"), Reasons: []string{"other"}, Dependencies: []Path{Keys("other")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a"), Reasons: []string{"parent"}, Dependencies: []Path{Keys("parent")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "b", "grand"), Reasons: []string{"deep", "shared"}, Dependencies: []Path{parsedDependency, Keys("deep")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Path{}, Reasons: []string{"root"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("outside"), Reasons: []string{"root child"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "b", "normalization"), Reasons: []string{"normalized"}, Origin: Origin{Operation: ChangeNormalization}}},
+		{change: Change{Path: Keys("a", "none"), Reasons: []string{"parent child"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+	}
+	want := coalescedResolutionSnapshotsByScan(snapshots)
+	got := coalescedResolutionSnapshots(snapshots)
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("coalesced snapshots differ from ordered scan:\n got: %#v\nwant: %#v", got, want)
+	}
+	if len(got) != 4 || got[0].change.Origin.Operation != ChangeNormalization ||
+		!reflect.DeepEqual(got[0].change.Reasons, []string{"child", "shared", "child", "deep", "normalized"}) ||
+		len(got[0].change.Dependencies) != 2 || got[3].change.Path.String() != "" {
+		t.Fatalf("coalesced ordering or unions changed: %#v", got)
+	}
+}
+
+func coalescedResolutionSnapshotsByScan(snapshots []resolutionSnapshot) []resolutionSnapshot {
+	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	for _, snapshot := range snapshots {
+		merged := false
+		for i := range groups {
+			if !pathContainsByPointer(groups[i].change.Path, snapshot.change.Path) {
+				continue
+			}
+			for _, reason := range snapshot.change.Reasons {
+				groups[i].change.Reasons = appendUniqueStringByScan(groups[i].change.Reasons, reason)
+			}
+			for _, dependency := range snapshot.change.Dependencies {
+				groups[i].change.Dependencies = appendUniquePathByPointer(groups[i].change.Dependencies, dependency)
+			}
+			if snapshot.change.Origin.Operation == ChangeNormalization {
+				groups[i].change.Origin.Operation = ChangeNormalization
+			}
+			merged = true
+			break
+		}
+		if !merged {
+			snapshot.change = cloneChange(snapshot.change)
+			groups = append(groups, snapshot)
+		}
+	}
+	return groups
+}
+
+func appendUniqueStringByScan(values []string, value string) []string {
+	if !slices.Contains(values, value) {
+		return append(values, value)
+	}
+	return values
+}
+
+func appendUniquePathByPointer(paths []Path, path Path) []Path {
+	for _, existing := range paths {
+		if existing.String() == path.String() {
+			return paths
+		}
+	}
+	return append(paths, path.clone())
+}
+
+func TestResolutionDependencyMembershipMatchesPointerSpelling(t *testing.T) {
+	parse := func(pointer string) Path {
+		path, err := ParsePath(pointer)
+		if err != nil {
+			t.Fatalf("ParsePath(%q) error = %v", pointer, err)
+		}
+		return path
+	}
+	paths := []Path{
+		Keys("a/b"), parse("/a~1b"),
+		Keys("a~1b"), parse("/a~01b"),
+		Keys("items").Index(0), parse("/items/0"), Keys("items", "0"),
+		Keys("items", "01"), parse("/items/01"),
+		Keys("-1"), parse("/-1"),
+		Keys("a", "b"), Keys("a/b"),
+	}
+	var record resolutionRecord
+	var want []Path
+	for _, path := range paths {
+		record.addDependency(path)
+		want = appendUniquePathByPointer(want, path)
+	}
+	if !reflect.DeepEqual(record.dependencies, want) {
+		t.Fatalf("resolution dependencies = %#v, want %#v", record.dependencies, want)
+	}
+}
+
+func TestResolutionCoverageIndexMatchesOrderedScan(t *testing.T) {
+	paths := []Path{
+		Keys("group"),
+		Keys("group", "field"),
+		Keys("group", "field"),
+		Keys("group", "field", "nested"),
+		Keys("other"),
+	}
+	records := make([]*resolutionRecord, len(paths))
+	snapshots := make([]resolutionSnapshot, len(paths))
+	for id, path := range paths {
+		records[id] = &resolutionRecord{path: path}
+		snapshots[id] = resolutionSnapshot{change: Change{Path: path}}
+	}
+	snapshotIndex, pointers := newResolutionCoverageIndexFromSnapshots(snapshots)
+	for id, pointer := range pointers {
+		if pointer != paths[id].String() {
+			t.Errorf("snapshot pointer %d = %q, want %q", id, pointer, paths[id].String())
+		}
+	}
+	queries := []Path{
+		Path{},
+		Keys("group"),
+		Keys("group", "field"),
+		Keys("group", "field", "nested", "leaf"),
+		Keys("group", "missing"),
+		Keys("other", "child"),
+		Keys("group").Index(-1),
+	}
+	for _, test := range []struct {
+		name  string
+		index *resolutionCoverageIndex
+	}{
+		{"records", newResolutionCoverageIndexFromRecords(records)},
+		{"snapshots", snapshotIndex},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			for _, query := range queries {
+				wantID, wantDepth, wantFound := 0, -1, false
+				for id, candidate := range paths {
+					if pathContainsByPointer(candidate, query) && (!wantFound || len(candidate.segments) > wantDepth) {
+						wantID, wantDepth, wantFound = id, len(candidate.segments), true
+					}
+				}
+				gotID, gotFound := test.index.deepestCoveringID(query)
+				if gotID != wantID || gotFound != wantFound {
+					t.Errorf("deepestCoveringID(%s) = %d, %v; want %d, %v", query.String(), gotID, gotFound, wantID, wantFound)
+				}
+			}
+		})
+	}
+}
+
+func TestDocumentLookupMatchesPathScan(t *testing.T) {
+	name := &document.Node{Kind: document.String, Text: "item"}
+	sequence := &document.Node{Kind: document.Sequence, Sequence: []*document.Node{
+		{Kind: document.String, Text: "zero"},
+		{Kind: document.Mapping, Mapping: []document.Entry{{Key: "name", Value: name}}},
+	}}
+	root := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{
+		{Key: "0", Value: &document.Node{Kind: document.String, Text: "numeric key"}},
+		{Key: "01", Value: &document.Node{Kind: document.String, Text: "leading zero key"}},
+		{Key: "items", Value: sequence},
+	}}
+	applicationRoot := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{
+		{Key: "shared", Value: sequence},
+		{Key: "application", Value: &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{Key: "value", Value: &document.Node{Kind: document.String, Text: "application"}}}}},
+	}}
+	lookup := buildDocumentLookup(root, applicationRoot)
+	paths := []Path{
+		Path{},
+		Keys("0"),
+		Keys("01"),
+		Keys("items"),
+		Keys("items").Index(0),
+		Keys("items").Index(1).Key("name"),
+		Keys("items").Index(2),
+		Keys("items").Key("name"),
+		Keys("missing"),
+		Keys("items").Index(-1),
+		(Path{}).Index(0),
+	}
+	for _, path := range paths {
+		wantNode, wantFound := documentAtPath(root, path)
+		gotNode, gotFound := documentAtPathWithLookup(root, path, lookup)
+		if gotNode != wantNode || gotFound != wantFound {
+			t.Errorf("indexed lookup %s = (%p, %v), want (%p, %v)", path.String(), gotNode, gotFound, wantNode, wantFound)
+		}
+	}
+	for _, path := range []Path{Path{}, Keys("shared"), Keys("shared").Index(1).Key("name"), Keys("application", "value")} {
+		wantNode, wantFound := documentAtPath(applicationRoot, path)
+		gotNode, gotFound := documentAtPathWithLookup(applicationRoot, path, lookup)
+		if gotNode != wantNode || gotFound != wantFound {
+			t.Errorf("indexed application lookup %s = (%p, %v), want (%p, %v)", path.String(), gotNode, gotFound, wantNode, wantFound)
+		}
+	}
+}
+
+func TestApplyResolutionMetadataPreservesOverlappingDeltaOrder(t *testing.T) {
+	oldOrigin := Origin{Layer: LayerBase}
+	parentOrigin := Origin{Layer: LayerResolution, Operation: ChangeNormalization}
+	childOrigin := Origin{Layer: LayerResolution, Operation: ChangeDerivedDefault}
+	leaf := &document.Node{Kind: document.String, Text: "value"}
+	final := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{
+		Key: "group",
+		Value: &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{
+			Key:   "item",
+			Value: &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{Key: "leaf", Value: leaf}}},
+		}}},
+	}}}
+	metadata := &Metadata{
+		fields:  map[string]FieldInfo{"/group/item/leaf": {Origin: oldOrigin}},
+		history: make(map[string][]Change),
+	}
+	resolved := resolutionResult{
+		final:  final,
+		deltas: []documentDelta{{path: Keys("group")}, {path: Keys("group", "item")}},
+		snapshots: []resolutionSnapshot{
+			{change: Change{Path: Keys("group"), Origin: parentOrigin}},
+			{change: Change{Path: Keys("group", "item"), Origin: childOrigin}},
+		},
+	}
+
+	applyResolutionMetadata(metadata, resolved)
+
+	field := metadata.fields["/group/item/leaf"]
+	if field.Origin.Operation != childOrigin.Operation {
+		t.Fatalf("final leaf origin operation = %q, want %q", field.Origin.Operation, childOrigin.Operation)
+	}
+	changes := metadata.history["/group/item/leaf"]
+	if len(changes) != 2 {
+		t.Fatalf("leaf history has %d entries, want 2: %#v", len(changes), changes)
+	}
+	if changes[0].Origin.Operation != parentOrigin.Operation || changes[1].Origin.Operation != childOrigin.Operation {
+		t.Fatalf("leaf history operations = %q, %q; want %q, %q", changes[0].Origin.Operation, changes[1].Origin.Operation, parentOrigin.Operation, childOrigin.Operation)
+	}
+	for index, change := range changes {
+		if len(change.Previous) != 1 || change.Previous[0].Layer != oldOrigin.Layer {
+			t.Errorf("leaf history[%d] Previous = %#v, want original origin", index, change.Previous)
+		}
+	}
+}

internal/engine/resolution_test.go

@@ -122,6 +122,11 @@ func TestResolutionPreservesExplicitNullAndZeroWhileReplacingAbsentBaseline(t *t
 func TestResolutionCoalescesEqualAndRepeatedHelperIntent(t *testing.T) {
 	t.Parallel()
 
+	parsedOther, err := ParsePath("/other")
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	type config struct {
 		Value int `yaml:"value"`
 		Other int `yaml:"other"`
@@ -130,8 +135,9 @@ func TestResolutionCoalescesEqualAndRepeatedHelperIntent(t *testing.T) {
 		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"))
-			Default(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", Keys("other"))
+			Default(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", parsedOther)
 			Normalize(resolution, Keys("value"), &configuration.Value, 7, "canonicalized value", Keys("other"))
+			Normalize(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", parsedOther)
 			return nil
 		},
 	}})
@@ -206,6 +212,31 @@ func TestResolutionSequenceReplacementUpdatesDescendantOrigins(t *testing.T) {
 	}
 }
 
+func TestOrderedResolutionRecordsSortEscapedPointers(t *testing.T) {
+	parsedIndex, err := ParsePath("/items/0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	records := map[string]*resolutionRecord{
+		"tilde":  {path: Keys("a~b")},
+		"slash":  {path: Keys("a/b")},
+		"nested": {path: Keys("a", "b")},
+		"index":  {path: Keys("items").Index(0)},
+		"parsed": {path: parsedIndex},
+		"last":   {path: Keys("z")},
+	}
+	ordered := orderedResolutionRecords(records)
+	want := []string{"/a/b", "/a~0b", "/a~1b", "/items/0", "/items/0", "/z"}
+	if len(ordered) != len(want) {
+		t.Fatalf("ordered records = %d, want %d", len(ordered), len(want))
+	}
+	for i, record := range ordered {
+		if got := record.path.String(); got != want[i] {
+			t.Fatalf("record[%d] path = %q, want %q", i, got, want[i])
+		}
+	}
+}
+
 func TestResolutionRejectsUnrecordedAndMismatchedMutations(t *testing.T) {
 	t.Parallel()
 

internal/engine/secret.go

@@ -9,17 +9,10 @@ type secretDependency struct {
 
 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)
+		walkDocument(application.value, application.path, func(path Path, _ *document.Node) {
-		indexDocument(application.value, application.path, applicationPaths)
+			addSecretPath(paths, path.String())
-		for pointer := range applicationPaths {
+		})
-			addSecretPath(paths, pointer)
-		}
 	}
 	var dependencies []secretDependency
 	for pointer, history := range metadata.history {
@@ -65,16 +58,19 @@ func classifySecretPaths(schema *schemaDescriptor, predicate func(Path) bool, me
 	}
 
 	secret := make(map[string]bool)
-	for _, tree := range append(projections, final) {
+	classifyProjection := func(tree *document.Node) {
-		projected := make(map[string]*document.Node)
+		walkDocument(tree, Path{}, func(path Path, node *document.Node) {
-		indexDocument(tree, Path{}, projected)
+			pointer := path.String()
-		for pointer, node := range projected {
 			addSecretPath(paths, pointer)
 			if node.Sensitive {
 				secret[pointer] = true
 			}
+		})
 	}
+	for _, tree := range projections {
+		classifyProjection(tree)
 	}
+	classifyProjection(final)
 	for pointer, path := range paths {
 		if root, ok := schemaSecretRoot(schema, path); ok {
 			secret[root.String()] = true
@@ -83,49 +79,29 @@ func classifySecretPaths(schema *schemaDescriptor, predicate func(Path) bool, me
 			secret[pointer] = true
 		}
 	}
-	for {
+	return closeSecretDependencies(paths, secret, dependencies, inherited)
-		changed := false
-		for _, dependency := range dependencies {
-			if secretIntersectsPath(paths, secret, dependency.dependency) && !secret[dependency.target.String()] {
-				secret[dependency.target.String()] = true
-				changed = true
-			}
-		}
-		for _, link := range inherited {
-			if pathIsSecret(secret, link.dependency) && !secret[link.target.String()] {
-				secret[link.target.String()] = true
-				changed = true
-			}
-			if pathIsSecret(secret, link.target) && !secret[link.dependency.String()] {
-				secret[link.dependency.String()] = true
-				changed = true
-			}
-		}
-		if !changed {
-			return secret
-		}
-	}
 }
 
 func addSecretPath(paths map[string]Path, pointer string) {
+	if existing, found := paths[pointer]; found && existing.valid() {
+		// Accumulator keys already match their paths' canonical spelling. History
+		// can install typed segments, which still need the parsed replacement.
+		parsed := true
+		for _, segment := range existing.segments {
+			if segment.kind != pathSegmentParsed {
+				parsed = false
+				break
+			}
+		}
+		if parsed {
+			return
+		}
+	}
 	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

internal/engine/secret_classification_test.go

@@ -0,0 +1,79 @@
+package engine
+
+import "testing"
+
+func TestSecretPathCollectionKeepsParsedContributions(t *testing.T) {
+	for _, pointer := range []string{"", "/", "/records/0", "/records/a~1b~0/01"} {
+		t.Run(pointer, func(t *testing.T) {
+			paths := make(map[string]Path)
+			for repeat := 0; repeat < 3; repeat++ {
+				addSecretPath(paths, pointer)
+				path, found := paths[pointer]
+				if !found || !path.valid() || path.String() != pointer {
+					t.Fatalf("collected path = %#v, found %v; want %q", path, found, pointer)
+				}
+				for _, segment := range path.segments {
+					if segment.kind != pathSegmentParsed {
+						t.Fatalf("collected path %q retained a typed segment: %#v", pointer, segment)
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestSecretClassificationParsesTypedHistoryAfterNumericShapeChanges(t *testing.T) {
+	tests := []struct {
+		name       string
+		earlier    string
+		final      string
+		historical Path
+	}{
+		{"mapping to sequence", "items: {'0': old}", "items: [new]", Keys("items", "0")},
+		{"sequence to mapping", "items: [old]", "items: {'0': new}", Keys("items").Index(0)},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			earlier := parseCompositionDocument(t, "earlier", test.earlier)
+			final := parseCompositionDocument(t, "final", test.final)
+			pointer := test.historical.String()
+			metadata := Metadata{history: map[string][]Change{pointer: {{Path: test.historical}}}}
+			seen := false
+			classified := classifySecretPaths(nil, func(path Path) bool {
+				if path.String() != pointer {
+					return false
+				}
+				seen = true
+				for _, segment := range path.segments {
+					if segment.kind != pathSegmentParsed {
+						t.Fatalf("predicate received typed history after final projection: %#v", path)
+					}
+				}
+				return true
+			}, metadata, final, []historyApplication{{value: earlier}}, earlier)
+			if !seen || !classified[pointer] {
+				t.Fatalf("historical/final numeric path was not classified: %#v", classified)
+			}
+		})
+	}
+}
+
+func TestSecretPredicateReceivesDetachedHistoricalPath(t *testing.T) {
+	path := Keys("records").Key("1")
+	metadata := Metadata{history: map[string][]Change{
+		path.String(): {{Path: path}},
+	}}
+	seen := false
+	classified := classifySecretPaths(nil, func(candidate Path) bool {
+		if candidate.String() != path.String() {
+			return false
+		}
+		seen = true
+		candidate.segments[0].key = "changed"
+		return true
+	}, metadata, nil, nil)
+
+	if !seen || !classified[path.String()] || classified["/changed/1"] {
+		t.Fatalf("classification after predicate mutation = %#v, predicate called: %v", classified, seen)
+	}
+}

internal/engine/secret_propagation.go

@@ -0,0 +1,69 @@
+package engine
+
+type secretTrigger struct {
+	target   string
+	ordinary bool
+}
+
+func closeSecretDependencies(paths map[string]Path, sensitive map[string]bool, dependencies, inherited []secretDependency) map[string]bool {
+	result := make(map[string]bool, len(sensitive))
+	queue := make([]string, 0, len(sensitive))
+	for pointer, classified := range sensitive {
+		if classified {
+			result[pointer] = true
+			queue = append(queue, pointer)
+		}
+	}
+
+	var triggers pathPrefixIndex
+	triggerValues := make([]secretTrigger, 0, len(dependencies)+2*len(inherited))
+	insert := func(dependency Path, target string, ordinary bool) {
+		if ordinary && !dependency.valid() {
+			return
+		}
+		id := len(triggerValues)
+		triggerValues = append(triggerValues, secretTrigger{target: target, ordinary: ordinary})
+		triggers.insert(dependency.String(), id)
+	}
+	for _, dependency := range dependencies {
+		insert(dependency.dependency, dependency.target.String(), true)
+	}
+	for _, link := range inherited {
+		insert(link.dependency, link.target.String(), false)
+		insert(link.target, link.dependency.String(), false)
+	}
+
+	fired := make([]bool, len(triggerValues))
+	activate := func(id int) {
+		if fired[id] {
+			return
+		}
+		fired[id] = true
+		target := triggerValues[id].target
+		if !result[target] {
+			result[target] = true
+			queue = append(queue, target)
+		}
+	}
+	for head := 0; head < len(queue); head++ {
+		pointer := queue[head]
+		if classified, ok := paths[pointer]; ok && classified.valid() {
+			triggers.visitAncestors(classified.String(), func(id int) {
+				if triggerValues[id].ordinary {
+					activate(id)
+				}
+			})
+			triggers.visitDescendants(classified.String(), func(id int) {
+				if triggerValues[id].ordinary {
+					activate(id)
+				}
+			})
+		}
+		triggers.visitDescendants(pointer, func(id int) {
+			if !triggerValues[id].ordinary {
+				activate(id)
+			}
+		})
+	}
+	return result
+}

internal/engine/secret_propagation_test.go

@@ -0,0 +1,147 @@
+package engine
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestSecretDependencyClosureMatchesFixedPointScan(t *testing.T) {
+	tests := []struct {
+		name            string
+		paths           map[string]Path
+		seed            map[string]bool
+		dependencies    []secretDependency
+		inherited       []secretDependency
+		wantSensitivity map[string]bool
+	}{
+		{
+			name:  "forward reverse chains and cycles",
+			paths: secretPaths(Keys("input"), Keys("derived"), Keys("output"), Keys("cycle")),
+			seed:  secretSet(Keys("input")),
+			dependencies: []secretDependency{
+				{dependency: Keys("input"), target: Keys("derived")},
+				{dependency: Keys("derived"), target: Keys("output")},
+				{dependency: Keys("output"), target: Keys("cycle")},
+				{dependency: Keys("cycle"), target: Keys("derived")},
+				{dependency: Keys("input"), target: Keys("derived")},
+			},
+		},
+		{
+			name:  "ordinary ancestor descendant and root relations",
+			paths: secretPaths(Path{}, Keys("branch", "leaf"), Keys("parent", "child")),
+			seed:  secretSet(Keys("branch", "leaf"), Keys("parent")),
+			dependencies: []secretDependency{
+				{dependency: Keys("branch"), target: Keys("from-descendant")},
+				{dependency: Keys("parent", "child"), target: Keys("from-ancestor")},
+				{dependency: Path{}, target: Keys("from-root")},
+			},
+		},
+		{
+			name:  "unindexed seed only activates inherited relations",
+			paths: secretPaths(Keys("ordinary"), Keys("copy")),
+			seed:  secretSet(Keys("untracked")),
+			dependencies: []secretDependency{
+				{dependency: Keys("untracked"), target: Keys("ordinary")},
+			},
+			inherited: []secretDependency{
+				{dependency: Keys("untracked"), target: Keys("copy")},
+			},
+			wantSensitivity: map[string]bool{"/copy": true, "/ordinary": false},
+		},
+		{
+			name:  "inheritance direction root escapes and numeric spellings",
+			paths: secretPaths(Path{}, Keys("a/b", "01"), Keys("source", "value")),
+			seed:  secretSet(Path{}),
+			dependencies: []secretDependency{
+				{dependency: Keys("a/b", "01"), target: Keys("ordinary-copy")},
+			},
+			inherited: []secretDependency{
+				{dependency: Keys("a/b", "01"), target: Keys("destination", "01")},
+				{dependency: Keys("source"), target: Keys("destination")},
+			},
+		},
+		{
+			name:  "inherited links do not trigger from classified descendants",
+			paths: secretPaths(Keys("parent", "secret", "nested")),
+			seed:  secretSet(Keys("parent", "secret", "nested")),
+			inherited: []secretDependency{
+				{dependency: Keys("parent", "secret"), target: Keys("child", "secret")},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			want := referenceSecretDependencyClosure(test.paths, test.seed, test.dependencies, test.inherited)
+			got := closeSecretDependencies(test.paths, test.seed, test.dependencies, test.inherited)
+			if !reflect.DeepEqual(got, want) {
+				t.Fatalf("closure = %#v, want %#v", got, want)
+			}
+			for pointer, sensitive := range test.wantSensitivity {
+				if got[pointer] != sensitive {
+					t.Errorf("sensitivity at %q = %v, want %v", pointer, got[pointer], sensitive)
+				}
+			}
+		})
+	}
+}
+
+func referenceSecretDependencyClosure(paths map[string]Path, seed map[string]bool, dependencies, inherited []secretDependency) map[string]bool {
+	secret := make(map[string]bool, len(seed))
+	for pointer, classified := range seed {
+		if classified {
+			secret[pointer] = true
+		}
+	}
+	for {
+		changed := false
+		for _, dependency := range dependencies {
+			if referenceSecretIntersectsPath(paths, secret, dependency.dependency) && !secret[dependency.target.String()] {
+				secret[dependency.target.String()] = true
+				changed = true
+			}
+		}
+		for _, link := range inherited {
+			if pathIsSecret(secret, link.dependency) && !secret[link.target.String()] {
+				secret[link.target.String()] = true
+				changed = true
+			}
+			if pathIsSecret(secret, link.target) && !secret[link.dependency.String()] {
+				secret[link.dependency.String()] = true
+				changed = true
+			}
+		}
+		if !changed {
+			return secret
+		}
+	}
+}
+
+func referenceSecretIntersectsPath(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 secretPaths(paths ...Path) map[string]Path {
+	result := make(map[string]Path, len(paths))
+	for _, path := range paths {
+		result[path.String()] = path
+	}
+	return result
+}
+
+func secretSet(paths ...Path) map[string]bool {
+	result := make(map[string]bool, len(paths))
+	for _, path := range paths {
+		result[path.String()] = true
+	}
+	return result
+}

internal/engine/snapshot.go

@@ -12,7 +12,11 @@ import (
 // Snapshot projection is the shared redaction boundary for effective YAML
 // and explanation values. It borrows frozen trees and returns a detached tree.
 func valueSnapshot(root *document.Node, path Path, secrets map[string]bool) ValueSnapshot {
-	node, present := documentAtPath(root, path)
+	return valueSnapshotWithLookup(root, path, secrets, nil)
+}
+
+func valueSnapshotWithLookup(root *document.Node, path Path, secrets map[string]bool, lookup *documentLookup) ValueSnapshot {
+	node, present := documentAtPathWithLookup(root, path, lookup)
 	if !present {
 		return ValueSnapshot{}
 	}

release_publish_test.go

@@ -1,359 +0,0 @@
-package configkit
-
-import (
-	"os"
-	"os/exec"
-	"path/filepath"
-	"strings"
-	"testing"
-)
-
-type releaseFixture struct {
-	t             *testing.T
-	root          string
-	remote        string
-	base          string
-	candidate     string
-	validationLog string
-	realGit       string
-}
-
-func newReleaseFixture(t *testing.T) *releaseFixture {
-	t.Helper()
-	realGit, err := exec.LookPath("git")
-	if err != nil {
-		t.Fatal(err)
-	}
-	f := &releaseFixture{
-		t:             t,
-		root:          t.TempDir(),
-		remote:        filepath.Join(t.TempDir(), "remote.git"),
-		validationLog: filepath.Join(t.TempDir(), "validator.log"),
-		realGit:       realGit,
-	}
-	f.git("init", "-q", "-b", "main")
-	f.git("init", "-q", "--bare", f.remote)
-	f.git("config", "user.name", "Test")
-	f.git("config", "user.email", "test@example.invalid")
-	f.git("config", "commit.gpgsign", "false")
-	f.git("config", "tag.gpgsign", "false")
-	f.git("config", "push.followTags", "true")
-	f.git("remote", "add", "origin", f.remote)
-	f.write(".gitignore", "ignored.log\n", 0600)
-	f.write("README.md", "fixture\n", 0600)
-	f.git("add", ".")
-	f.git("commit", "-qm", "Initial source")
-	f.base = f.git("rev-parse", "HEAD")
-	f.git("push", f.remote, "HEAD:refs/heads/main")
-
-	script, err := os.ReadFile("scripts/release.sh")
-	if err != nil {
-		t.Fatal(err)
-	}
-	// Only the fixture copy substitutes the authoritative endpoint.
-	local := strings.ReplaceAll(string(script), "https://gitea.maximumdirect.net/eric/ConfigKit.git", f.remote)
-	f.write("scripts/release.sh", local, 0700)
-	f.write("scripts/release-check.sh", `#!/bin/sh
-printf 'validate\n' >> "$CONFIGKIT_VALIDATION_LOG"
-case "${CONFIGKIT_VALIDATOR_ACTION-}" in
-  fail) exit 37 ;;
-  change) git commit --allow-empty -qm 'Changed during validation' ;;
-  dirty) printf 'changed\n' > unexpected.txt ;;
-  remote-tag) git --git-dir="$CONFIGKIT_REMOTE" update-ref refs/tags/v0.9.0 "$CONFIGKIT_BASE" ;;
-esac
-`, 0700)
-	f.write("docs/releases/v0.9.0.md", "# ConfigKit v0.9.0\n\nConfiguration loading fixes.\n\nCompatibility is unchanged.\n", 0600)
-	f.git("add", ".")
-	f.git("commit", "-qm", "Prepared source")
-	f.candidate = f.git("rev-parse", "HEAD")
-	return f
-}
-
-func (f *releaseFixture) write(path, contents string, mode os.FileMode) {
-	f.t.Helper()
-	target := filepath.Join(f.root, path)
-	if err := os.MkdirAll(filepath.Dir(target), 0700); err != nil {
-		f.t.Fatal(err)
-	}
-	if err := os.WriteFile(target, []byte(contents), mode); err != nil {
-		f.t.Fatal(err)
-	}
-}
-
-func (f *releaseFixture) git(args ...string) string {
-	f.t.Helper()
-	cmd := exec.Command(f.realGit, args...)
-	cmd.Dir = f.root
-	cmd.Env = append(os.Environ(), "GIT_ALLOW_PROTOCOL=file", "GIT_CONFIG_NOSYSTEM=1", "GIT_CONFIG_GLOBAL=/dev/null")
-	out, err := cmd.CombinedOutput()
-	if err != nil {
-		f.t.Fatalf("git %v: %v\n%s", args, err, out)
-	}
-	return strings.TrimSpace(string(out))
-}
-
-func (f *releaseFixture) gitResult(args ...string) (string, error) {
-	f.t.Helper()
-	cmd := exec.Command(f.realGit, args...)
-	cmd.Dir = f.root
-	cmd.Env = append(os.Environ(), "GIT_ALLOW_PROTOCOL=file", "GIT_CONFIG_NOSYSTEM=1", "GIT_CONFIG_GLOBAL=/dev/null")
-	out, err := cmd.CombinedOutput()
-	return strings.TrimSpace(string(out)), err
-}
-
-func (f *releaseFixture) run(version, behavior, validatorAction string) (string, error) {
-	f.t.Helper()
-	bin := f.t.TempDir()
-	wrapper := `#!/bin/sh
-if [ "${CONFIGKIT_GIT_BEHAVIOR-}" = main-unknown ] || [ "${CONFIGKIT_GIT_BEHAVIOR-}" = tag-unknown ]; then
-  if [ "${1-}" = ls-remote ] && [ -f "$CONFIGKIT_GIT_MARKER" ]; then exit 37; fi
-fi
-case "$*" in
-  push\ *|-c\ remote.origin.mirror=false\ push\ *)
-  case "$*" in
-    *refs/heads/main*)
-      case "${CONFIGKIT_GIT_BEHAVIOR-}" in
-        main-lost) "$CONFIGKIT_REAL_GIT" "$@" >/dev/null 2>&1; exit 37 ;;
-        main-reject) exit 37 ;;
-        main-unknown) : > "$CONFIGKIT_GIT_MARKER"; exit 37 ;;
-      esac ;;
-    *refs/tags/v0.9.0*)
-      case "${CONFIGKIT_GIT_BEHAVIOR-}" in
-        tag-lost) "$CONFIGKIT_REAL_GIT" "$@" >/dev/null 2>&1; exit 37 ;;
-        tag-reject) exit 37 ;;
-        tag-conflict)
-          "$CONFIGKIT_REAL_GIT" --git-dir="$CONFIGKIT_REMOTE" update-ref refs/tags/v0.9.0 "$CONFIGKIT_BASE"
-          exit 37 ;;
-        tag-unknown) : > "$CONFIGKIT_GIT_MARKER"; exit 37 ;;
-      esac ;;
-  esac
-  ;;
-esac
-exec "$CONFIGKIT_REAL_GIT" "$@"
-`
-	if err := os.WriteFile(filepath.Join(bin, "git"), []byte(wrapper), 0700); err != nil {
-		f.t.Fatal(err)
-	}
-	nested := filepath.Join(f.root, "nested")
-	if err := os.Mkdir(nested, 0700); err != nil {
-		f.t.Fatal(err)
-	}
-	cmd := exec.Command("/bin/bash", filepath.Join(f.root, "scripts", "release.sh"), version)
-	cmd.Dir = nested
-	cmd.Env = append(os.Environ(),
-		"PATH="+bin+string(os.PathListSeparator)+os.Getenv("PATH"),
-		"GIT_ALLOW_PROTOCOL=file", "GIT_CONFIG_NOSYSTEM=1", "GIT_CONFIG_GLOBAL=/dev/null",
-		"CONFIGKIT_VALIDATION_LOG="+f.validationLog,
-		"CONFIGKIT_VALIDATOR_ACTION="+validatorAction,
-		"CONFIGKIT_GIT_BEHAVIOR="+behavior,
-		"CONFIGKIT_GIT_MARKER="+filepath.Join(bin, "push-seen"),
-		"CONFIGKIT_REAL_GIT="+f.realGit,
-		"CONFIGKIT_REMOTE="+f.remote,
-		"CONFIGKIT_BASE="+f.base,
-	)
-	out, err := cmd.CombinedOutput()
-	return string(out), err
-}
-
-func (f *releaseFixture) validations() int {
-	f.t.Helper()
-	data, err := os.ReadFile(f.validationLog)
-	if os.IsNotExist(err) {
-		return 0
-	}
-	if err != nil {
-		f.t.Fatal(err)
-	}
-	return strings.Count(string(data), "validate\n")
-}
-
-func (f *releaseFixture) remoteRef(ref string) string {
-	f.t.Helper()
-	value, err := f.gitResult("--git-dir="+f.remote, "rev-parse", "--verify", ref)
-	if err != nil {
-		return ""
-	}
-	return value
-}
-
-func TestReleasePublicationGuards(t *testing.T) {
-	for _, scenario := range []string{
-		"success", "main-already-current", "ignored-file", "unrelated-tag",
-		"malformed-version", "wrong-branch", "wrong-destination", "multiple-destinations",
-		"dirty-worktree", "changed-candidate", "missing-note", "mismatched-note",
-		"local-tag", "remote-tag", "remote-tag-after-validation",
-		"dirty-after-validation", "remote-query-failure",
-		"failed-validation", "non-fast-forward",
-	} {
-		t.Run(scenario, func(t *testing.T) {
-			f := newReleaseFixture(t)
-			version := "v0.9.0"
-			validatorAction := ""
-			switch scenario {
-			case "main-already-current":
-				f.git("push", f.remote, "HEAD:refs/heads/main")
-			case "ignored-file":
-				f.write("ignored.log", "local only\n", 0600)
-			case "unrelated-tag":
-				f.git("tag", "-a", "-m", "Unrelated", "v0.8.0", f.base)
-			case "malformed-version":
-				version = "v00.9.0"
-			case "wrong-branch":
-				f.git("checkout", "-qb", "feature")
-			case "wrong-destination":
-				other := filepath.Join(t.TempDir(), "other.git")
-				f.git("init", "-q", "--bare", other)
-				f.git("remote", "set-url", "--push", "origin", other)
-			case "multiple-destinations":
-				f.git("remote", "set-url", "--push", "origin", f.remote)
-				f.git("remote", "set-url", "--add", "--push", "origin", filepath.Join(t.TempDir(), "other.git"))
-			case "dirty-worktree":
-				f.write("untracked.txt", "unexpected\n", 0600)
-			case "changed-candidate":
-				validatorAction = "change"
-			case "dirty-after-validation":
-				validatorAction = "dirty"
-			case "missing-note":
-				f.git("rm", "docs/releases/v0.9.0.md")
-				f.git("commit", "-qm", "Remove note")
-			case "mismatched-note":
-				f.write("docs/releases/v0.9.0.md", "# ConfigKit v0.9.1\n", 0600)
-				f.git("add", ".")
-				f.git("commit", "-qm", "Mismatch note")
-			case "local-tag":
-				f.git("tag", "v0.9.0")
-			case "remote-tag":
-				f.git("tag", "v0.9.0")
-				f.git("push", f.remote, "refs/tags/v0.9.0")
-				f.git("tag", "-d", "v0.9.0")
-			case "remote-tag-after-validation":
-				validatorAction = "remote-tag"
-			case "remote-query-failure":
-				if err := os.Rename(f.remote, f.remote+".unavailable"); err != nil {
-					t.Fatal(err)
-				}
-			case "failed-validation":
-				validatorAction = "fail"
-			case "non-fast-forward":
-				f.git("checkout", "-qb", "other", f.base)
-				f.git("commit", "--allow-empty", "-qm", "Divergent source")
-				f.git("push", f.remote, "HEAD:refs/heads/main")
-				f.git("checkout", "main")
-			}
-			out, err := f.run(version, "", validatorAction)
-			success := scenario == "success" || scenario == "main-already-current" ||
-				scenario == "ignored-file" || scenario == "unrelated-tag"
-			if success != (err == nil) {
-				t.Fatalf("unexpected publication result: %v\n%s", err, out)
-			}
-			wantChecks := 1
-			switch scenario {
-			case "malformed-version", "wrong-branch", "wrong-destination",
-				"multiple-destinations", "dirty-worktree", "missing-note",
-				"mismatched-note", "local-tag", "remote-tag", "remote-query-failure",
-				"non-fast-forward":
-				wantChecks = 0
-			}
-			if got := f.validations(); got != wantChecks {
-				t.Fatalf("validator ran %d times, want %d", got, wantChecks)
-			}
-			if success {
-				if got := f.remoteRef("refs/heads/main"); got != f.candidate {
-					t.Fatalf("published main %s, want %s", got, f.candidate)
-				}
-				if got := f.remoteRef("refs/tags/v0.9.0^{}"); got != f.candidate {
-					t.Fatalf("tag points to %s, want %s", got, f.candidate)
-				}
-				if f.remoteRef("refs/tags/v0.8.0") != "" {
-					t.Fatal("unrelated local tag was published")
-				}
-				tagData := f.git("--git-dir="+f.remote, "cat-file", "-p", "refs/tags/v0.9.0")
-				_, message, ok := strings.Cut(tagData, "\n\n")
-				if !ok || strings.TrimSpace(message) != strings.TrimSpace(f.git("show", f.candidate+":docs/releases/v0.9.0.md")) {
-					t.Fatal("annotated tag does not contain the checked-in note")
-				}
-			} else if scenario != "remote-tag" && scenario != "remote-tag-after-validation" &&
-				f.remoteRef("refs/tags/v0.9.0") != "" {
-				t.Fatal("failed guard published a tag")
-			}
-		})
-	}
-}
-
-func TestReleasePublicationRecovery(t *testing.T) {
-	for _, scenario := range []string{
-		"main-lost", "main-reject", "main-unknown",
-		"tag-lost", "tag-reject", "tag-conflict", "tag-unknown",
-	} {
-		t.Run(scenario, func(t *testing.T) {
-			f := newReleaseFixture(t)
-			out, err := f.run("v0.9.0", scenario, "")
-			success := scenario == "main-lost" || scenario == "tag-lost"
-			if success != (err == nil) {
-				t.Fatalf("unexpected publication result: %v\n%s", err, out)
-			}
-			if got := f.validations(); got != 1 {
-				t.Fatalf("validator ran %d times", got)
-			}
-			remoteMain := f.remoteRef("refs/heads/main")
-			remoteTag := f.remoteRef("refs/tags/v0.9.0")
-			localTag, localTagErr := f.gitResult("rev-parse", "--verify", "refs/tags/v0.9.0")
-			if localTagErr != nil {
-				localTag = ""
-			}
-			switch scenario {
-			case "main-lost", "tag-lost":
-				if remoteMain != f.candidate || remoteTag == "" || remoteTag != localTag {
-					t.Fatal("confirmed publication did not preserve exact refs")
-				}
-			case "main-reject", "main-unknown":
-				if remoteMain != f.base || remoteTag != "" || localTag != "" {
-					t.Fatal("failed main push created publication state")
-				}
-			case "tag-reject", "tag-unknown":
-				if remoteMain != f.candidate || remoteTag != "" || localTag == "" {
-					t.Fatal("failed tag push did not retain branch-only state")
-				}
-			case "tag-conflict":
-				if remoteMain != f.candidate || remoteTag != f.base || localTag == "" {
-					t.Fatal("conflicting remote tag was overwritten")
-				}
-			}
-		})
-	}
-}
-
-func TestReleasePublicationUsesValidatedDestination(t *testing.T) {
-	for _, behavior := range []string{"success", "main-lost", "tag-lost"} {
-		t.Run(behavior, func(t *testing.T) {
-			f := newReleaseFixture(t)
-			other := filepath.Join(t.TempDir(), "other.git")
-			f.git("init", "-q", "--bare", other)
-			f.git("remote", "set-url", "--push", "origin", f.remote)
-			f.git("config", "url."+other+".pushInsteadOf", f.remote)
-			// These defaults must not broaden the explicit release refspecs when
-			// publishing through the validated named remote.
-			f.git("config", "remote.origin.mirror", "true")
-			f.git("config", "remote.origin.push", "refs/heads/*:refs/heads/*")
-			f.git("branch", "unrelated", f.base)
-			f.git("tag", "-a", "-m", "Unrelated", "v0.8.0", f.base)
-			f.git("--git-dir="+f.remote, "update-ref", "refs/heads/keep", f.base)
-
-			out, err := f.run("v0.9.0", behavior, "")
-			if err != nil {
-				t.Fatalf("publish: %v\n%s", err, out)
-			}
-			if f.validations() != 1 || f.remoteRef("refs/heads/main") != f.candidate ||
-				f.remoteRef("refs/tags/v0.9.0") != f.git("rev-parse", "refs/tags/v0.9.0") {
-				t.Fatal("publication did not reach the validated destination")
-			}
-			if f.remoteRef("refs/heads/keep") != f.base ||
-				f.remoteRef("refs/heads/unrelated") != "" || f.remoteRef("refs/tags/v0.8.0") != "" {
-				t.Fatal("publication changed unrelated refs")
-			}
-			if refs := f.git("--git-dir="+other, "for-each-ref", "--format=%(refname)"); refs != "" {
-				t.Fatalf("publication reached the rewrite destination: %s", refs)
-			}
-		})
-	}
-}

releasekit.json

@@ -0,0 +1,12 @@
+{
+  "product": "ConfigKit",
+  "remote": "origin",
+  "expected_push_url": "https://gitea.maximumdirect.net/eric/ConfigKit.git",
+  "validation": {
+    "go": {
+      "race": true,
+      "full_vet": true,
+      "compile_targets": ["linux/amd64", "linux/arm64"]
+    }
+  }
+}

releasekit_profile_test.go

@@ -0,0 +1,57 @@
+package configkit
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestReleaseKitProfile(t *testing.T) {
+	data, err := os.ReadFile("releasekit.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var profile struct {
+		Product         string `json:"product"`
+		Remote          string `json:"remote"`
+		ExpectedPushURL string `json:"expected_push_url"`
+		Validation      struct {
+			Go struct {
+				Race           bool     `json:"race"`
+				FullVet        bool     `json:"full_vet"`
+				CompileTargets []string `json:"compile_targets"`
+			} `json:"go"`
+		} `json:"validation"`
+	}
+
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&profile); err != nil {
+		t.Fatalf("decode release profile: %v", err)
+	}
+
+	if profile.Product != "ConfigKit" {
+		t.Errorf("product = %q, want ConfigKit", profile.Product)
+	}
+	if profile.Remote != "origin" {
+		t.Errorf("remote = %q, want origin", profile.Remote)
+	}
+	wantPushURL := "https://gitea.maximumdirect.net/eric/ConfigKit.git"
+	if fixturePushURL := os.Getenv("CONFIGKIT_TEST_EXPECTED_PUSH_URL"); fixturePushURL != "" {
+		wantPushURL = fixturePushURL
+	}
+	if profile.ExpectedPushURL != wantPushURL {
+		t.Errorf("expected push URL = %q, want %q", profile.ExpectedPushURL, wantPushURL)
+	}
+	goValidation := profile.Validation.Go
+	if !goValidation.Race || !goValidation.FullVet {
+		t.Errorf("race and full vet must be selected: race=%t full_vet=%t", goValidation.Race, goValidation.FullVet)
+	}
+	wantTargets := []string{"linux/amd64", "linux/arm64"}
+	if !reflect.DeepEqual(goValidation.CompileTargets, wantTargets) {
+		t.Errorf("compile targets = %v, want %v", goValidation.CompileTargets, wantTargets)
+	}
+}

scripts/release-check.sh

@@ -1,29 +0,0 @@
-#!/usr/bin/env bash
-set -euo pipefail
-
-repository_dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)
-cd "$repository_dir"
-
-baseline_toolchain=${CONFIGKIT_BASELINE_TOOLCHAIN:?set CONFIGKIT_BASELINE_TOOLCHAIN to a cached supported Go 1.25 patch release}
-
-run_go() {
-  local toolchain=$1
-  shift
-  GOTOOLCHAIN="$toolchain" GOPROXY=off go "$@"
-}
-
-if ! GOTOOLCHAIN="$baseline_toolchain" GOPROXY=off go version >/dev/null; then
-  printf 'release toolchain %s is unavailable; acquire it before validation\n' "$baseline_toolchain" >&2
-  exit 1
-fi
-
-# Verbose output reports skipped cases without a separate evidence run.
-run_go "$baseline_toolchain" test -mod=readonly -vet=off -race -v ./...
-run_go "$baseline_toolchain" vet -mod=readonly ./...
-
-# Only release-validated targets gate publication; macOS is best-effort.
-for target in linux/amd64 linux/arm64; do
-  target_os=${target%/*}
-  target_arch=${target#*/}
-  GOTOOLCHAIN="$baseline_toolchain" GOPROXY=off CGO_ENABLED=0 GOOS="$target_os" GOARCH="$target_arch" go build -mod=readonly ./...
-done

scripts/release.sh

@@ -1,133 +0,0 @@
-#!/usr/bin/env bash
-set -euo pipefail
-
-repository_dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)
-cd "$repository_dir"
-
-remote_url=https://gitea.maximumdirect.net/eric/ConfigKit.git
-
-fail() {
-  printf '%s\n' "$*" >&2
-  exit 1
-}
-
-check_candidate() {
-  local context=$1 current status
-  current=$(git branch --show-current) || fail "$context: cannot read the current branch"
-  [[ "$current" == main ]] || fail "$context: release requires the main branch"
-  status=$(git status --porcelain=v1 --untracked-files=all) || fail "$context: cannot inspect the worktree"
-  [[ -z "$status" ]] || fail "$context: release requires a clean index and worktree"
-  current=$(git rev-parse --verify HEAD) || fail "$context: cannot identify the candidate"
-  [[ "$current" == "$candidate" ]] || fail "$context: candidate changed; commit and validate it again"
-}
-
-check_unused_version() {
-  if git show-ref --verify --quiet "refs/tags/$version"; then
-    fail "version already has a local tag"
-  fi
-  local oid result
-  if oid=$(read_remote_ref "refs/tags/$version"); then
-    fail "version already has an authoritative tag"
-  else
-    result=$?
-    ((result == 2)) || fail "cannot determine authoritative tag state; publication status is unknown"
-  fi
-}
-
-read_remote_ref() {
-  local ref=$1 response result
-  if response=$(git ls-remote --refs --exit-code origin "$ref" 2>/dev/null); then
-    [[ "$response" == *$'\t'"$ref" ]] || return 3
-    printf '%s\n' "${response%%$'\t'*}"
-  else
-    result=$?
-    ((result == 2)) && return 2
-    return 3
-  fi
-}
-
-if (($# != 1)); then
-  fail "usage: ./scripts/release.sh vMAJOR.MINOR.PATCH"
-fi
-version=$1
-[[ "$version" =~ ^v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$ ]] ||
-  fail "release version must be a stable vMAJOR.MINOR.PATCH without leading zeroes"
-
-fetch_urls=$(git remote get-url --all origin 2>/dev/null) || fail "origin is unavailable"
-push_urls=$(git remote get-url --push --all origin 2>/dev/null) || fail "origin push destination is unavailable"
-[[ "$fetch_urls" == "$remote_url" && "$push_urls" == "$remote_url" ]] ||
-  fail "origin must have exactly the authoritative fetch and push destination"
-
-candidate=$(git rev-parse --verify HEAD) || fail "cannot identify the candidate"
-check_candidate "before validation"
-check_unused_version
-
-note_path="docs/releases/$version.md"
-note_file=$(mktemp)
-trap 'rm -f -- "$note_file"' EXIT
-git show "$candidate:$note_path" >"$note_file" 2>/dev/null ||
-  fail "matching release note is absent from the candidate"
-IFS= read -r title <"$note_file" || [[ -n "$title" ]] ||
-  fail "matching release note is empty"
-[[ "$title" == "# ConfigKit $version" ]] || fail "release note title does not match the version"
-
-if remote_main=$(read_remote_ref refs/heads/main); then
-  :
-else
-  result=$?
-  ((result == 2)) && fail "authoritative main is absent"
-  fail "cannot read authoritative main; publication status is unknown"
-fi
-git fetch --no-tags origin refs/heads/main >/dev/null ||
-  fail "cannot fetch authoritative main"
-fetched_main=$(git rev-parse --verify FETCH_HEAD) || fail "cannot inspect fetched main"
-git merge-base --is-ancestor "$fetched_main" "$candidate" ||
-  fail "candidate cannot advance authoritative main without discarding history"
-
-./scripts/release-check.sh || fail "release validation failed; no refs were published"
-check_candidate "after validation"
-check_unused_version
-
-# Use the named remote whose resolved destinations were checked above: a literal
-# URL can apply pushInsteadOf even when origin's explicit push URL does not.
-# Disable mirror defaults as well as implicit tags; publish only our refspec.
-if git -c remote.origin.mirror=false push --no-follow-tags origin "$candidate:refs/heads/main"; then
-  :
-else
-  if observed_main=$(read_remote_ref refs/heads/main); then
-    [[ "$observed_main" == "$candidate" ]] ||
-      fail "main push did not publish candidate $candidate; authoritative main differs"
-  else
-    result=$?
-    ((result == 2)) && fail "main push failed for $candidate; authoritative main is absent"
-    fail "main push outcome is unknown for $candidate; inspect authoritative main before retrying"
-  fi
-fi
-
-check_candidate "main at $candidate; tag not yet published"
-git tag -a -F "$note_file" --cleanup=verbatim "$version" "$candidate" ||
-  fail "main is at $candidate; could not create local tag $version"
-tag_target=$(git rev-parse --verify "refs/tags/$version^{}") ||
-  fail "main is at $candidate; cannot verify local tag $version"
-[[ "$tag_target" == "$candidate" ]] || fail "main is at $candidate; local tag $version targets another commit"
-tag_type=$(git cat-file -t "refs/tags/$version") ||
-  fail "main is at $candidate; cannot inspect local tag $version"
-[[ "$tag_type" == tag ]] || fail "main is at $candidate; local tag $version is not annotated"
-tag_oid=$(git rev-parse --verify "refs/tags/$version") ||
-  fail "main is at $candidate; cannot identify local tag $version"
-
-if git -c remote.origin.mirror=false push --no-follow-tags origin "refs/tags/$version:refs/tags/$version"; then
-  :
-else
-  if observed_tag=$(read_remote_ref "refs/tags/$version"); then
-    [[ "$observed_tag" == "$tag_oid" ]] ||
-      fail "authoritative tag $version conflicts with the local tag at $candidate; never replace it"
-  else
-    result=$?
-    ((result == 2)) &&
-      fail "tag push failed; main is at $candidate, but local tag $version is unpublished"
-    fail "tag $version push outcome is unknown for $candidate; retain the local tag and inspect authoritative state"
-  fi
-fi
-
-printf 'Published %s at %s\n' "$version" "$candidate"

startup_bench_test.go

@@ -0,0 +1,159 @@
+package configkit_test
+
+import (
+	"fmt"
+	"net/url"
+	"slices"
+	"strings"
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+// These synthetic types retain the optional-field shape of a catalog consumer
+// without importing its adapter, template compiler, or runtime registries.
+type startupCatalog struct {
+	Profiles map[string]startupProfile           `yaml:"profiles"`
+	Prompts  map[string]map[string]startupPrompt `yaml:"prompts"`
+}
+
+type startupProfile struct {
+	Backend         *string        `yaml:"backend"`
+	Endpoint        *string        `yaml:"endpoint"`
+	Model           *string        `yaml:"model"`
+	Temperature     *float64       `yaml:"temperature"`
+	TopP            *float64       `yaml:"top_p"`
+	MaxTokens       *int           `yaml:"max_tokens"`
+	TimeoutSeconds  *int           `yaml:"timeout_seconds"`
+	ServiceTier     *string        `yaml:"service_tier"`
+	ReasoningEffort *string        `yaml:"reasoning_effort"`
+	APIKeyEnv       *string        `yaml:"api_key_env"`
+	APIKeyRequired  *bool          `yaml:"api_key_required"`
+	ExtraParams     map[string]any `yaml:"extra_params"`
+}
+
+type startupPrompt struct {
+	DefaultProfile *string          `yaml:"default_profile"`
+	Description    *string          `yaml:"description"`
+	SessionID      *string          `yaml:"session_id"`
+	Inputs         []startupInput   `yaml:"inputs"`
+	Messages       []startupMessage `yaml:"messages"`
+	Output         *startupOutput   `yaml:"output"`
+}
+
+type startupInput struct {
+	Name        string  `yaml:"name"`
+	Required    bool    `yaml:"required"`
+	ContentType *string `yaml:"content_type"`
+	Description *string `yaml:"description"`
+}
+
+type startupMessage struct {
+	Role        *string `yaml:"role"`
+	Content     *string `yaml:"content"`
+	ContentFile *string `yaml:"content_file"`
+}
+
+type startupOutput struct {
+	Format         *string `yaml:"format"`
+	ValidationMode *string `yaml:"validation_mode"`
+	SchemaPath     *string `yaml:"schema_path"`
+	RepairAttempts int     `yaml:"repair_attempts"`
+}
+
+type startupPresence struct{ explicit, null bool }
+
+var startupResult *configkit.Result[startupCatalog]
+
+func BenchmarkStartupConstruction(b *testing.B) {
+	for _, count := range []int{32, 128, 512} {
+		b.Run(fmt.Sprint(count), func(b *testing.B) {
+			profiles, prompts := make(map[string]any, count), make(map[string]any, count)
+			for index := range count {
+				profileID := fmt.Sprintf("profile-%03d", index)
+				promptID := fmt.Sprintf("prompt-%03d", index)
+				profiles[profileID] = map[string]any{"endpoint": "https://example.test/v1", "model": profileID}
+				prompts[promptID] = map[string]any{"1": map[string]any{
+					"default_profile": profileID,
+					"messages":        []any{map[string]any{"role": "user", "content": "Hello {{.name}}"}},
+					"output":          map[string]any{"format": "text", "validation_mode": "none"},
+				}}
+			}
+			// Mapping captures the source once outside timing, matching the
+			// downstream benchmark's reusable input. Each load still owns its result.
+			main := configkit.Input{Source: configkit.Mapping("startup catalog", map[string]any{
+				"profiles": profiles, "prompts": prompts,
+			})}
+			var captured map[string]map[string]startupPresence
+			validated := false
+			options := configkit.LayeredOptions[startupCatalog]{Definition: configkit.Definition[startupCatalog]{
+				// Include a simple path-based classifier, as catalog consumers use
+				// this callback even when the representative input has no credentials.
+				Secret: func(path configkit.Path) bool {
+					return strings.HasSuffix(path.String(), "/extra_params/token")
+				},
+				Resolve: func(catalog *startupCatalog, resolution *configkit.Resolution) error {
+					captured = make(map[string]map[string]startupPresence, len(catalog.Profiles))
+					for id, profile := range catalog.Profiles {
+						fields := make(map[string]startupPresence, 12)
+						for _, field := range []string{
+							"backend", "endpoint", "model", "temperature", "top_p", "max_tokens",
+							"timeout_seconds", "service_tier", "reasoning_effort", "api_key_env",
+							"api_key_required", "extra_params",
+						} {
+							info, exists := resolution.InputInfo(configkit.Keys("profiles", id, field))
+							fields[field] = startupPresence{explicit: exists && info.Explicit, null: exists && info.Null}
+						}
+						captured[id] = fields
+						// The representative endpoints are already canonical, so this
+						// callback, like the consumer's, records no normalization change.
+						if _, err := url.Parse(*profile.Endpoint); err != nil {
+							return err
+						}
+					}
+					return nil
+				},
+				Validate: func(catalog *startupCatalog, validation *configkit.Validation) {
+					validated = true
+					ids := make([]string, 0, len(catalog.Profiles))
+					for id := range catalog.Profiles {
+						ids = append(ids, id)
+					}
+					slices.Sort(ids)
+					for _, id := range ids {
+						profile := catalog.Profiles[id]
+						if profile.Model == nil || strings.TrimSpace(*profile.Model) == "" {
+							validation.Error(configkit.Keys("profiles", id, "model"), "model is required")
+						}
+					}
+				},
+			}}
+			// Check the measured workload before timing, including numeric mapping
+			// keys, sequence paths, callback presence capture, and published metadata.
+			result, err := configkit.LoadLayered(main, options)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if !validated || len(result.Config.Profiles) != count || len(result.Config.Prompts) != count || len(captured) != count {
+				b.Fatal("startup fixture did not exercise the expected lifecycle")
+			}
+			fields := captured["profile-000"]
+			if !fields["endpoint"].explicit || !fields["model"].explicit || fields["temperature"].explicit {
+				b.Fatal("startup fixture presence capture disagrees with input")
+			}
+			path := configkit.Keys("prompts", "prompt-000", "1", "messages").Index(0).Key("content")
+			if info, exists := result.Metadata().Lookup(path); !exists || !info.Explicit || info.Null {
+				b.Fatal("startup fixture message provenance is missing")
+			}
+			b.ReportAllocs()
+			for b.Loop() {
+				result, err := configkit.LoadLayered(main, options)
+				if err != nil {
+					b.Fatal(err)
+				}
+				startupResult = result
+			}
+			b.ReportMetric(float64(count*2), "definitions/op")
+		})
+	}
+}