Expose sequence placement controls in the public API

internal/engine/sequence_registration.go

@@ -9,6 +9,22 @@ type sequencePolicy struct {
 	identityFields map[string]string
 }
 
+// DefinitionWithSequenceRegistrations attaches facade-owned registrations to a
+// detached engine definition without exposing the registration representation.
+func DefinitionWithSequenceRegistrations[T any](definition Definition[T], paths []Path, identityFields []string) Definition[T] {
+	if paths == nil {
+		definition.sequenceRegistrations = nil
+		return definition
+	}
+	definition.sequenceRegistrations = make([]sequenceRegistration, len(paths))
+	for index := range paths {
+		definition.sequenceRegistrations[index] = sequenceRegistration{
+			path: paths[index].clone(), identityField: identityFields[index],
+		}
+	}
+	return definition
+}
+
 func compileSequencePolicy(registrations []sequenceRegistration) (sequencePolicy, []Diagnostic) {
 	policy := sequencePolicy{identityFields: make(map[string]string, len(registrations))}
 	var diagnostics []Diagnostic