Expose sequence identity registrations through the facade

lifecycle.go

@@ -15,15 +15,11 @@ type Definition[T any] struct {
 	Validate func(*T, *Validation)
 	Version  *VersionRule
 	Secret   func(Path) bool
-	// SequenceCompositions registers mapping paths whose sequence contributions
-	// strictly append distinct records by the selected literal identity field.
-	// Invalid or conflicting registrations fail option validation. Repeated input
-	// identities fail strict composition after source and helper processing. The
-	// field also supplies identity for parent lookup when surviving records at
-	// that path use record-inheritance directives.
-	// Registration paths are copied when a load begins; definitions are read-only
-	// after being shared.
-	SequenceCompositions []SequenceComposition
+	// 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.
+	SequenceIdentities []SequenceIdentity
 }
 
 // PlacementMode selects how an input mapping is placed at its Destination.
@@ -38,20 +34,6 @@ const (
 	PlacementModeSequenceItem
 )
 
-// SequenceComposition registers a sequence path for strict identity-based
-// composition. Path is copied at load start; IdentityField is one literal key,
-// including the empty string. Invalid or conflicting registrations fail option
-// validation.
-type SequenceComposition struct {
-	// Path selects a literal mapping path; registration paths are copied at load
-	// start. Invalid paths fail option validation; the root path is harmless.
-	Path Path
-	// IdentityField is one literal mapping key and may be empty. Records must
-	// contain a string at this key; malformed records fail strict composition.
-	// The field also identifies parents for record inheritance at this path.
-	IdentityField string
-}
-
 // SourceVersionMode controls schema-version declarations across one complete
 // load. The zero value preserves the existing main-only effective-path check
 // and its protected-path behavior. Enabled modes check participating documents
@@ -360,14 +342,12 @@ func toEngineFilesystemContext(context *FilesystemContext) *engine.FilesystemCon
 
 func toEngineDefinition[T any](definition Definition[T]) engine.Definition[T] {
 	result := engine.Definition[T]{Defaults: definition.Defaults}
-	if definition.SequenceCompositions != nil {
-		paths := make([]engine.Path, len(definition.SequenceCompositions))
-		identityFields := make([]string, len(definition.SequenceCompositions))
-		for index, registration := range definition.SequenceCompositions {
-			paths[index] = toEnginePath(registration.Path.clone())
-			identityFields[index] = registration.IdentityField
+	if definition.SequenceIdentities != nil {
+		registrations := make([]engine.SequenceIdentityRegistrationInput, len(definition.SequenceIdentities))
+		for index, identity := range definition.SequenceIdentities {
+			registrations[index] = toEngineSequenceIdentity(identity)
 		}
-		result = engine.DefinitionWithSequenceRegistrations(result, paths, identityFields)
+		result = engine.DefinitionWithSequenceIdentityRegistrations(result, registrations)
 	}
 	if definition.Resolve != nil {
 		result.Resolve = func(configuration *T, resolution *engine.Resolution) error {