Clarify final identity validation and overlay semantics

docs/config.md

@@ -971,7 +971,9 @@ and typed decoding. Overlay bytes, nodes, and source records count toward the sa
 aggregate limits as base inputs. Its canonical path must remain within the configured
 root and must not duplicate a file already present in the base graph.
 
-Overlay is intentionally distinct from strict composition:
+Collection destinations follow the
+[collection operation and presence rules](#strict-document-composition) above.
+The following table describes ordinary overlay behavior elsewhere:
 
 | Existing lower node | Incoming overlay node | Result |
 | --- | --- | --- |
@@ -980,9 +982,10 @@ Overlay is intentionally distinct from strict composition:
 | Mapping | Mapping | Recurse by mapping key |
 | Any other pair of present nodes | Any other pair of present nodes | Replace the entire lower node |
 
-Scalars, sequences, and null are atomic. Thus an overlay sequence replaces rather
-than extends a base sequence, `[]` clears it, null is an explicit replacement, and
-cross-kind replacement is allowed when the final application schema accepts it.
+Under these ordinary rules, scalars, sequences, and null are atomic. An overlay
+sequence replaces rather than extends a base sequence, `[]` clears it, null is an
+explicit replacement, and cross-kind replacement is allowed when the final
+application schema accepts it.
 Replacing a subtree removes all displaced descendants from effective presence and
 origin data; history retains the displaced definitions and identifies the parent
 replacement. Surviving overlay paths have overlay origins, while recursively shared

docs/roadmap/remediation.md

@@ -348,7 +348,13 @@ English wording or exposing identity values.
 
 ## 10. Remove Stale Public Contract Descriptions — P2
 
-Status: [ ] Open.
+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).

lifecycle.go

@@ -17,8 +17,10 @@ type Definition[T any] struct {
 	Secret   func(Path) bool
 	// SequenceIdentities declares the scalar fields used to combine records and
 	// resolve record inheritance at selected sequence destinations. Registration
-	// errors are reported before source acquisition. These constraints do not yet
-	// validate identities introduced by defaults, CLI overrides, or callbacks.
+	// errors are reported before source acquisition. Before successful return,
+	// matching final sequences are also checked, including values from defaults,
+	// CLI overrides, and application resolution. Schema and validation govern
+	// path existence and shape; later caller mutations are outside this guarantee.
 	SequenceIdentities []SequenceIdentity
 }