Clarify final identity validation and overlay semantics

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
 }