# Sequence Implementation Review Remediation Status: findings 1–11 are complete. The subsequent integration audit at `8d40983271de5239312eb0a2896737be88c5abdc` identified six additional open findings, numbered 12–17 below. This record introduces no new release gate. Reviewed commit: `0be7cdb00eff576fda6b30c0600b2134d4e2e086`. Implementation range: `bc6b977..0be7cdb`. Authority: the [sequence roadmap](sequences.md), [implementation plan](implementation.md), [ADR 0017](../adr/0017-collection-sequence-policy.md), and [ADR 0018](../adr/0018-cli-after-structural-resolution.md). The public facade, shared identity/composition machinery, scoped policies, identified-record inheritance, post-decode CLI phase, and final registered identity validation are present. The findings below concern remaining correctness, contract-alignment, documentation, and scaling gaps. Validation on the reviewed commit: - `./scripts/check.sh` passed with Go 1.26.10 on Linux. - `go test -race ./...` passed. - Public-API probes outside the repository reproduced findings 1–9. The probes used labeled byte sources, defaults, and an in-memory filesystem; they did not change implementation files or use external services. - Finding 10 follows directly from the maintained text; finding 11 follows from the prefix-scan loop, not a timing comparison or performance threshold. Validation after the initial remediation: `./scripts/check.sh` and `go test -race ./...` passed with Go 1.26.10 on Linux. The original public-API probes for findings 1–9 now demonstrate the required corrected behavior. P1 denotes the highest-priority correctness issue here; P2 denotes normal-priority work needed to complete the selected behavior. Preserve the agreed scope while fixing these issues. In particular, do not resolve failures by restricting valid identity fields, requiring repeated declarations, changing merge semantics, or adding limits. ## 1. Preserve Retained Explicit Values In Nested CLI Mapping Assignments — P1 Status: [x] Complete. Completion: override metadata now reads the actual target subtree through one shared lookup. Ordinary/layered regressions preserve retained values, including zero and false, their explicit origins, and absence-based resolver behavior. Verified `go test ./internal/engine -run 'Override|CLI' -count=1` and `./scripts/check.sh`. Owner: [`applyDecodedOverrides`](../../internal/engine/override_decode.go), especially lines 59–60 and the presence/origin update helpers. The helpers receive the complete configuration projection as `existing`, but interpret it as the subtree at the override path. A partial nested mapping therefore treats retained input children as absent and drops their presence and origins. `fillDefaultOrigins` subsequently labels those retained values as defaults. Reproduction: load the following into ordinary nested Go structs: ```yaml settings: nested: a: 1 b: 2 ``` Apply an override at `[settings]` with value `map[string]any{"nested": map[string]any{"a": 3}}`. The typed value of `b` initially remains 2, but `Metadata.Lookup([settings,nested,b])` reports `Explicit: false` and a default origin. Calling `Default` for that field in application resolution then changes the explicitly supplied 2 to the fallback value. This violates presence-based defaulting, not merely presentation. Required remediation: use the actual existing target subtree when updating presence/origins, preserving retained descendants and removing genuinely replaced ones. Keep override batches detached and preserve the selected post-decode order. Add regressions for nested partial mappings, retained zero/false values, metadata, and an absence-based resolver default that must not overwrite retained input. ## 2. Read Upsert Origins At Input Paths And Write Them At Output Paths — P2 Status: [x] Complete. Completion: sequence origin copying now separates incoming and effective paths for precedence and inheritance. A regression covers reordered matches, appended records, composite origins, and actual resource reads from distinct declaring directories. Verified focused origin/inheritance/overlay/provenance tests, `go test -race ./internal/engine`, and `./scripts/check.sh`. Owners: [`applyOverlaySequenceEvidence`](../../internal/engine/overlay.go), particularly lines 369 and 381, and the analogous sequence-origin copying in [`inheritance_collection.go`](../../internal/engine/inheritance_collection.go). The overlay helper supplies an output-index path to an origin lookup whose keys are still incoming-index paths. When those positions differ and another incoming record occupies the output index, metadata takes that other record's source location. The same defect was reproduced through mapping-sibling inheritance; its helper uses the same single-path copying pattern. Reproduction: an underlay supplies IDs `[a,b]`; the main source declares `key: id` and supplies `[b*,a*]`. The result is correctly `[a*,b*]`, but the value origin for final `a*` is the source line of `b*`, and vice versa. In the probe the two value lines were 7 and 9; final index 0 incorrectly reported line 7 instead of 9. With separately authored records this can select a different source/context. Required remediation: use the operation's input-to-output projection for origin subtree reads as well as writes. Preserve composite contributing origins, not just node-location fallbacks. Test reordered upserts and appended records with distinct source files/locations, including nested fields, inheritance operations, and declaring resource contexts. ## 3. Apply Tier Sequence Operations To Historical Contributions — P2 Status: [x] Complete. Completion: per-source history now composes strict item projections with the tier operation, including nested application prefixes and local sequence replay. Regressions cover all three operations, multiple peers, retained records, removed fields, source attribution, and a subsequent overlay without a false decoding event. Verified focused history tests, `go test -race ./internal/engine`, and `./scripts/check.sh`. Owner: [`applyOverlayWithCollectionPolicy`](../../internal/engine/overlay.go), lines 76–84, and existing sequence-history projection/replay. For composed tiers, `applications` is nonempty. This branch appends the tier's original strict-composition applications without incorporating the newly computed precedence sequence descriptors. Replay consequently performs a whole-list replacement or strict append rather than the actual cross-tier upsert/append. The later decoding reconciliation conceals the mismatch by attributing a structural combination to typed defaults/decoding. Reproduction: lower `[a,b]` and higher `[b*,a*]` correctly yield `[a*,b*]`. `Explain([items])` instead shows the main contribution producing `[b*,a*]`, then a `decoding` event reordering it to `[a*,b*]` with the reason "applied retained defaults and canonical typed decoding". No decoder performed that reordering. Required remediation: project each retained per-source application through the tier's selected operation while keeping peer composition distinct from tier precedence. Do not collapse authored sources or fake decoding events. Cover upsert, append, unmatched retained records, reordered matches, removed fields, multiple higher-tier peers, and a subsequent selected overlay. Replay should agree with structural assembly before real decoding reconciliation. ## 4. Reproject Nested Source Destinations After Cross-Tier Item Movement — P2 Status: [x] Complete. Completion: layered assembly projects incoming source destinations and version classification evidence with the same item assignments used for values/history. Earlier contributions retain their historical coordinates, physical identities and contexts. Main/underlay regressions cover reordered upserts, append, replace, nested helpers, and source-local version evidence. Verified focused destination, origin and source-version tests, focused race coverage, and `./scripts/check.sh`. Owners: [`projectAcquiredDestinations`](../../internal/engine/imports.go) and the sequence-operation handoff in [`assembleLayeredInput`](../../internal/engine/load_request.go). Source destinations are projected while composing their own tier, but are not reprojected when that tier's records move to accumulated-list positions. Nested helper source records can therefore point at a different final record. Reproduction: lower `items` contains `[a,b]`. Main imports a single `b` record with `placement: sequence-item` into `[items]`; that record imports a helper mapping supplying its value. Upsert retains `a` at index 0 and places the higher `b` at index 1. `Sources()` nevertheless reports the surviving helper's destination as `/items/0`, its tier-local position, rather than `/items/1`. Required remediation: carry the sequence operation's projection through nested source-destination/evidence updates at precedence boundaries. Keep physical source identity and passive resource contexts unchanged, and preserve historical meaning for displaced contributions rather than relabeling them as survivors. Test a retained lower record followed by an imported higher record, reordered matches, and nested helpers. Check version-evidence projection where applicable. ## 5. Honor Identity Reset On Actual Inheritance Replacement — P2 Status: [x] Complete. Completion: inheritance resolves identity against actual child-value presence, discarding parent YAML identity for an explicit replacement while preserving agreement for retained values and authoritative application constraints. Added policy-state and public-load regressions for changed/unkeyed/non-sequence replacements, application agreement/conflict, and mode-only/append/upsert cases. Verified focused inheritance tests and `./scripts/check.sh`. Owners: [`inheritanceCollectionResolution` and `mergeInheritanceCollectionPolicies`](../../internal/engine/inheritance_collection.go), especially lines 79–80 and 121. These paths reconcile the parent's YAML identity before accounting for actual replacement, and treat the parent's collection as retained even when the child supplies a replacing value. This is stronger than the selected identity lifetime and differs from source-tier replacement. Reproduction: ```yaml configkit: sequences: - destination: [base, items] key: id - destination: [child, items] key: name mode: replace base: items: - id: a value: parent child: extends: base items: - name: b value: child ``` Loading fails with `sequence.conflict` at `/child/items`. It should succeed: actual whole-sequence replacement may discard the parent's YAML identity and establish `name`. Authoritative application constraints must still apply. Required remediation: distinguish actual replacement from a mode-only declaration before identity agreement and transfer. Test a changed key, replacement with no new key becoming unkeyed, permitted non-sequence replacement, and an agreeing or conflicting application registration. Preserve rejection of identity changes without a replacement value and during append/upsert. ## 6. Enforce Collection Operations Beneath Newly Added Ancestors — P2 Status: [x] Complete. Completion: copying a mapping now visits nested collection operations with absent lower values, preserving ordinary ancestor removal and whole-record semantics. Incoming record-owned policy transfers through the same operation. Regressions cover absent/empty/null ancestors, identity and kind failures, empty and valid initialization, and later inheritance using an imported item's nested identity. Corrected an older test that deferred the required error until a later tier. Verified focused merge/collection/inheritance tests, focused ownership race coverage, and `./scripts/check.sh`. Owners: [`mergeRecursiveMappings`](../../internal/engine/recursive_merge.go) and [`mergeOverlayMappingsWithCollectionPolicy`](../../internal/engine/overlay.go). When an incoming ancestor mapping is absent below, the recursive merger clones the entire subtree and invokes only its ancestor-level added hook. Nested collection resolutions are not visited. This bypasses their operation rules; the subsequent declaration-only policy update does not replace those checks. Reproduction: combine a lower `{}` with this main tier: ```yaml configkit: sequences: - destination: [group, items] mode: append group: items: - id: a ``` Loading succeeds despite append having no identity definition. Placing the same sequence directly at `[items]` correctly fails. The validity of an operation must not depend on whether an enclosing mapping already existed. Required remediation: account for applicable nested collection policies when adding/copying an ancestor subtree, including owned-policy transfer. Test absent and present enclosing mappings, append/upsert without identity, explicit empty lists, invalid non-sequence contributions, and valid identified initialization. Do not turn this into a general path-existence or shape constraint: ordinary ancestor replacement/removal retains its documented meaning. ## 7. Validate Final Typed Identity Fields As Payload, Not Directives — P2 Status: [x] Complete. Completion: shared identity lookup now distinguishes structural records from effective payload/reference mappings. Final validation includes literal `extends` fields while structural source checks still exclude actual directives. Facade regressions cover defaults and recorded resolution, string/null components, and duplicate rejection. Verified those regressions and existing structural identity and inheritance coverage through `./scripts/check.sh`. Owners: [`validateFinalSequenceIdentities`](../../internal/engine/final_identity.go) and [`newSequenceMappingIndex`](../../internal/engine/sequence_identity.go). The final validator reuses structural record lookup, which excludes every `extends` entry. At this phase there is no structural processing: typed defaults and application resolution can produce ordinary payload with that literal name. The roadmap expressly distinguishes structural-control exclusion from final typed-payload validation; this reuse introduces an extra restriction. Reproduction: a defaults-only `Catalog` with `Items []map[string]any` containing `{"extends": "application-data"}`, registered with `SequenceIdentityAt(Keys("items"), "extends")`, fails with a missing identity field at `/items/0/extends`, even though the effective field is present. Required remediation: distinguish structural-payload lookup from final payload lookup. Preserve rejection when a source tries to use an actual consumed directive as identity. Test final fields supplied by defaults and recorded resolution, including a null component, without adding a broader name ban. ## 8. Retain Nonfatal Main-Version Diagnostics In Layered Loads — P2 Status: [x] Complete. Completion: layered assembly returns nonfatal main-version diagnostics on success and alongside later failures; the shared caller stops only for errors. Regression coverage verifies ordinary/layered warning parity, exactly one checker call, and warnings retained with later structural or decoding errors. Verified through `./scripts/check.sh`, including existing source-version ordering coverage. Owner: [`assembleLayeredInput`](../../internal/engine/load_request.go), lines 143–152. The moved default-mode version-check call returns its diagnostics only when they contain errors. Warning-only diagnostics are discarded. Ordinary loading still retains the same warnings. Reproduction: a `VersionRule.Check` that calls `validation.Warning(Keys("version"), "test warning")` and returns nil yields one `version.warning` through ordinary `Load`, but zero diagnostics through `LoadLayered` with the same main input and default source-version mode. Required remediation: carry warnings from the single main-tier check into the shared diagnostic accumulator on successful layered loads. Preserve checker ownership, invocation count, and the selected acquisition/composition ordering. Add ordinary/layered parity and warning-plus-later-error regressions. ## 9. Identify Conflicting Application Registrations In Diagnostics — P2 Status: [x] Complete. Completion: definition validation retains original one-based registration positions and names both positions in each overlap diagnostic. No input path or new public diagnostic structure is invented. A mixed-selector regression verifies multiple conflicts even after an earlier invalid registration is skipped. Verified registration/facade coverage through `./scripts/check.sh`. Owner: [`compileSequenceIdentityPolicy`](../../internal/engine/sequence_registration.go), lines 119–128. Incompatible dynamic overlaps produce only a generic `options.invalid` message, an empty configuration path, and no related information. Neither registration is identified. The roadmap requires definition-time errors to identify the conflicting registrations without inventing a concrete input destination. Reproduction: register `collections -> AnyMappingKey -> items` using `id`, and `collections -> foo -> items` using `name`. Even with `NoSource`, the error is only "overlapping sequence registrations must use the same identity fields". With multiple registrations the caller cannot identify the conflicting pair. Required remediation: retain original registration positions and identify both in safe definition diagnostics, for example through positional message context. No new public diagnostic structure is required solely for this. Test mixed exact and dynamic registrations and multiple conflicts, without asserting complete English wording or exposing identity values. ## 10. Remove Stale Public Contract Descriptions — P2 Status: [x] Complete. Completion: the public definition comment now describes final registered-identity validation and its shape/lifetime boundaries. Selected-overlay prose explicitly separates ordinary replacement from collection policy and links to the canonical operation/presence tables. Verified against the implementation, local-link tests, and `git diff --check`; no runtime behavior changed. Owners: [`Definition.SequenceIdentities`](../../lifecycle.go), lines 18–21, and the [selected-overlay contract](../config.md#selected-overlays). The exported definition-field comment still says registrations do not validate identities introduced by defaults, CLI, or callbacks. Final validation is now implemented and the registration constructors correctly document it. The selected-overlay table and following paragraph also still unconditionally describe sequences as atomic replacements and `[]` as clearing. A later paragraph describes collection operations, but does not make the earlier unconditional claims accurate: identified collections infer upsert, and `[]` then contributes no records rather than clearing. Required remediation: make the symbol comment describe its implemented final guarantee and boundaries, and qualify the overlay table/paragraph for collection policy. Link to the canonical collection tables rather than duplicating them. Keep YAML-only enforcement distinct from registered final validation. ## 11. Remove The Quadratic Prefix Scan In Item Policy Projection — P2 Status: [x] Complete. Completion: assigned sequence ranges now supply item offsets directly. Handoffs without a range lazily accumulate prefix lengths, visiting each preceding contribution once rather than rescanning every prefix. Regression coverage keeps inline and policy-less contributions in the correct positions with complete, partial, or absent ranges. Existing ownership/placement tests remain intact. Verified focused item-policy tests, `./scripts/check.sh`, `go test -race ./...`, and inspection of the remaining error-only prefix-scan callers. No new benchmark fixture or performance threshold was needed for this bounded change. Owner: [`projectNestedCollectionPolicies`](../../internal/engine/imports.go), especially line 968; the scanned helper is `priorSequenceLength` in the same file. For every item with local collection policy, the loop scans all preceding contributions to calculate `itemIndex`, then overwrites that result when the already-indexed sequence range is available. For N such items this performs `0 + 1 + ... + (N-1)` contribution visits, excluding path lookup costs, despite the common case already having the exact assigned index. This is introduced quadratic work in the feature's independently authored-record path. Required remediation: use the existing assigned range first. If a genuine fallback is necessary, maintain per-destination prefix lengths in one pass rather than rescanning every prefix. Preserve scope and ordering semantics; do not add limits, pooling, or a new public cache. Keep ownership/placement regressions and add a representative many-item/local-policy benchmark only if needed to exercise the path. A wall-clock threshold is not required. ## Integration Audit Baseline And Scope Reviewed commit: `8d40983271de5239312eb0a2896737be88c5abdc`. This follow-up reviews the interaction of collection policy, identified-record inheritance, dynamic registrations, and post-decode CLI assignment with existing source placement, source-version checking, typed decoding, inspection, resource contexts, and ownership boundaries. The accepted ADRs and current configuration contract remain the authority; the findings require integration corrections, not additional consumer restrictions or new feature choices. Validation: - `./scripts/check.sh` and `go test -race ./...` pass with Go 1.26.10 on Linux. - Isolated public-API probes outside the repository reproduce findings 12–15. They use labeled byte sources and an in-memory filesystem, with no external services, real credentials, or repository implementation changes. - Finding 16 follows from the per-item deep-copy loop; no timing claim or performance threshold is needed. Finding 17 follows from maintained contract text that contradicts the implemented collection operations. - Positive comparisons include sequence-valued identity replacement, ancestor retirement through source tiers, quoted versions after item movement, and an append overlay that preserves the main record's version. ## 12. Complete Identity Retirement Across Replacement Shapes — P2 Status: [x] Complete. Completion: source composition and inheritance now prepare eligible lower policy from actual replacement paths before agreement. Removed identity and record state cannot constrain a new pending key or reappear in later inheritance. Shared mode selection preserves explicit-mode persistence and authoritative registrations. Regressions cover null/scalar/mapping/list replacement, ancestor removal with a new key, reintroduction, and retained/application-constrained conflicts. Verified focused retirement/inheritance tests, engine ownership race coverage, and `./scripts/check.sh`. Owners: [`resolveStrictCollectionPolicies`](../../internal/engine/compose.go), especially its `sequencePresent` reset condition; [`mergeInheritanceCollectionPolicies`](../../internal/engine/inheritance_collection.go); and ancestor-replacement handling in [`applyInheritanceScopeTemplates`](../../internal/engine/inheritance_schedule.go). Policy agreement and retirement still treat some actual replacements as retained collections. This has three observable effects under the same selected lifetime rule: 1. Source precedence accepts a replacement sequence with a new YAML key, but rejects the equivalent replacement by null or a scalar. For example, a lower tier declaring `key: id` for `[items]` with `items: [{id: old}]`, followed by a main tier declaring `key: name, mode: replace` with `items: null`, fails with `sequence.conflict` at `/items`. Replacing null with `42` also fails; replacing it with `[{name: new}]` succeeds. Null/scalar replacement should discard the lower identity and retain the newly declared key as pending policy, subject to the application's schema and constraints. 2. Removing an ancestor while declaring a new pending key for its removed descendant fails before the replacement occurs. A lower `group: {items: [{id: old}]}` with key `id`, followed by `group: null` and a root declaration of key `name` for `[group, items]`, fails at `/group/items`. The analogous `base`/`child` inheritance case fails at `/child/group/items`. The old collection is being removed rather than retained. 3. Inheritance can resurrect removed identity even without a conflicting new declaration. This input fails with a missing `id` at `/grandchild/group/items/0/id`: ```yaml configkit: sequences: [{destination: [base, group, items], key: id}] base: {group: {items: [{id: old}]}} child: extends: base group: null grandchild: extends: child group: {items: [{name: new}]} ``` The same remove/reintroduce operations through source tiers succeed. The inherited descendant identity remains in policy state after its enclosing mapping is removed, so the grandchild incorrectly receives the old key. Required remediation: account for actual value and ancestor replacement before deciding which lower identity participates in agreement, and retire removed descendant/record-owned state during inheritance as during source precedence. Retained inheritance templates must not reestablish discarded identity later. Preserve authoritative application constraints, independently owned mode persistence, pending declarations, and rejection of key changes when values are genuinely retained. Cover direct non-sequence replacement, ancestor removal with a new pending key, and removal followed by reintroduction across both contexts. Do not require repeated keys or narrow permitted null/scalar shapes to avoid these cases. ## 13. Keep Metadata History In Post-Decode CLI Order — P2 Status: [x] Complete. Completion: metadata history is assembled from the pre-CLI source view, with CLI events appended separately; inheritance is projected before CLI and resolution. Effective fields still describe post-CLI values. Regressions verify chronological origins and resolver dependencies for ordinary/layered mapping and record inheritance, including equal-valued assignments. Verified history/override coverage and `./scripts/check.sh`. Owners: [`historyWithInheritance`](../../internal/engine/inheritance_history.go) and the source/CLI metadata handoff in [`preparePostDecodeOverrideContext`](../../internal/engine/override_context.go). The value explanation follows the new lifecycle, but `Metadata.History` still inserts inheritance after stored CLI changes. `historyWithInheritance` splits only at `LayerResolution`, reflecting the former CLI-before-inheritance order. The reconstructed source view can also append an authored source origin after the CLI event. Reproduction: load `base: {value: parent}` and `child: {extends: base, value: authored}`, then override `[child, value]` with `"cli"`. The final value and `Metadata.Lookup` correctly report CLI provenance. `Explain` reports source → inheritance → CLI. `Metadata.History` instead reports source → CLI → source → inheritance and ends with a source/inheritance origin. This violates chronological metadata history and disagrees with the effective origin and the value explanation. Required remediation: assemble metadata history in the implemented source, inheritance, CLI, and resolution order, preserving the real origins and dependencies of those events. Cover ordinary/layered loading, mapping and record inheritance, equal-valued CLI writes, and a later recorded resolver change at the appropriate existing test owners. Do not impose a new exact event-count or message-format contract. ## 14. Carry Main-Version Coordinates Through Sequence Movement — P2 Status: [x] Complete. Completion: the effective version rule now follows the main declaration through strict placement, tier combination, and inheritance without changing source-local checker/evidence paths. Underlay and overlay ownership checks use assigned record positions, including whole-record removal; integer conversion remains confined to the actual main header. Regressions cover mounted/indexed paths, appended and matched records, integer/string parity, unrelated version payload, imported underlay claims, and inheritance. Corrected an older ownership fixture to target the actual matching main record. Verified source-version regressions, `./scripts/check.sh`, and `go test -race ./internal/engine`. Owners: [`effectiveSourceVersionRuleForPlacement`](../../internal/engine/source_version.go), the main-tier projection handoff in [`assembleLayeredInput`](../../internal/engine/load_request.go), and use of the effective rule in [`executeLoadRequest`](../../internal/engine/load.go). Source destinations and version-evidence sensitivity paths follow item movement, but the rule used for integer-version decoding retains the original item index. Consequently an accepted integer header can fail decoding after an otherwise valid upsert placement. Reproduction with the public API: - Main input is `id: main` and `version: 4`, placed as one sequence item at `Keys("items")`. - A lower input contributes the sequence item `id: lower` at the same destination. - Register identity `id` for `[items]`, select `SourceVersionModeIfPresent`, and use `VersionRule.Path = Keys("version")` with an accepting checker. - Decode into records with `ID string` and `Version string`. The checker accepts `4` exactly once. Upsert places the main record at index 1, but decoding fails with `decode.type` at `/items/1/version`. The integer-to-string exception is still tied to `/items/0/version`. Quoting the identical version as `'4'` succeeds. A source-local indexed header path, without item placement, reproduces the same problem when its record moves during upsert. Required remediation: carry the main declaration's effective coordinates through the existing item projections into decoding and audit the associated ownership protection handoffs for the same stale-coordinate assumption. Preserve source-local checker/evidence paths, checker invocation count, main-only ownership, and the narrow integer-to-string exception. Cover moved existing and newly appended main records, integer/string parity, and protection of the actual main header after movement. Do not prohibit supported indexed paths or mounted main records as a workaround. ## 15. Exclude Parent Identity From Inherited History Payload — P2 Status: [x] Complete. Completion: retained record-inheritance operations now exclude parent identity from their payload and origin projection. Replay preserves the child's own identity before taking field, record, sequence, or root snapshots, without inventing inheritance events for retained identity fields. Regressions cover single and compound identities, explicit child provenance, ordinary inherited payload, and the parent's original history. Verified inheritance/inspection coverage, `./scripts/check.sh`, and `go test -race ./internal/engine`. Owners: inheritance operation construction in [`applyInheritanceScopeTemplates`](../../internal/engine/inheritance_schedule.go), [`appendInheritanceExplanation`](../../internal/engine/inheritance_explain.go), and transferred-origin projection in [`inheritance_history.go`](../../internal/engine/inheritance_history.go). Identified-record value construction excludes the parent's identity fields, but the retained history operation still supplies the complete parent record and its identity origins to the older mapping-inheritance replay machinery. Reproduction: ```yaml configkit: sequences: [{destination: [items], key: id}] items: - id: base value: parent - id: child extends: {id: base} ``` The effective child ID and origin are correct. However, `Explain(Keys("items").Index(1).Key("id"))` reports `child` → `base` → `child`, attributing the intermediate value to an inheritance operation and the parent's ID location. `Metadata.History` likewise claims an inherited parent-ID contribution. That identity is expressly excluded from inherited payload; it was never an applied value at the child path. Required remediation: make history replay and transferred-origin projection use the same identity exclusion as value construction. Preserve the child's authored identity and presence, ordinary inherited payload history, and the parent record's own source history at its original path. Cover compound identities and identity fields alongside inherited payload at both record and ancestor queries; keep the existing inspection API and sensitivity behavior. ## 16. Avoid Deep-Copying Accumulated Item Policies Per Record — P2 Status: [ ] Open. Owners: [`projectNestedCollectionPolicies`](../../internal/engine/imports.go) and its use of copying `collectionPolicyScope.at` / `set` helpers in [`collection_policy_state.go`](../../internal/engine/collection_policy_state.go). The prefix-scan correction in finding 11 is present, but a separate quadratic cost remains on the same independently authored-record path. For every imported item with local policy, `at` deep-clones the destination's accumulated record order and every retained record's nested scope. After adding one owner, `set` deep-clones the growing policy again. With N fixed-size item-local policies at one destination, this copies approximately `1 + 2 + ... + N` retained scopes, even when every assigned sequence range is available. This follows directly from the loop and `cloneCollectionPolicy`; no busy-host timing comparison is required. It is an integration cost from reusing detached read/write helpers within private incremental construction, rather than from the required final ownership copies. Required remediation: construct each destination's owned record-policy state without repeatedly cloning all earlier records, retaining necessary copies at ownership boundaries. Preserve record ordering, distinct owners, sparse assigned positions, fallback offsets, and cross-load detachment. Reuse the existing item policy and ownership tests; add allocation/scaling evidence only where useful. Do not introduce public caches, pooling, new caps, or performance thresholds. ## 17. Reconcile Legacy Sequence-History Contract Text — P2 Status: [ ] Open. Owner: the metadata/provenance and explanation sections of [`docs/config.md`](../config.md#layered-metadata). The metadata section still says that a later tier supplying a sequence records replacement at the sequence path and that history does not imply identity-based merging across tiers. That describes the former unconditional replacement model, not the implemented append/upsert history or the collection operation tables in the same document. The explanation paragraph about atomic sequences also needs review so readers can distinguish snapshot/diff granularity from collection combination semantics. Required remediation: describe history for the selected collection operation and link to the canonical operation tables. Preserve the existing atomic sequence snapshot/diff behavior and whole-record upsert semantics; correcting the prose does not authorize recursive record-field merging, a new query API, or broader history guarantees.