Move profile composition to the engine facade

engine.go

@@ -350,13 +350,7 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 		promptDefs = promptdef.NewFilesystemRepository(cfg.PromptDir)
 	}
 
-	profiles := builtin.NewRepositoryWithDirectory(cfg.ProfileDir)
-	if options.profileSource {
-		profiles = builtin.NewRepositoryWithPrimary(options.profiles)
-	}
-	if options.memorySource {
-		profiles = profile.NewOverlayRepository(options.memoryProfiles, profiles)
-	}
+	profiles := newProfileRepository(cfg.ProfileDir, options)
 
 	backendRegistry, err := backend.NewRegistry(options.backends)
 	if err != nil {
@@ -409,6 +403,22 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 	}, nil
 }
 
+func newProfileRepository(profileDir string, options engineOptions) profile.Repository {
+	repository := builtin.NewRepository()
+
+	if options.profileSource {
+		repository = profile.NewOverlayRepository(options.profiles, repository)
+	} else if strings.TrimSpace(profileDir) != "" {
+		repository = profile.NewOverlayRepository(profile.NewFilesystemRepository(profileDir), repository)
+	}
+
+	if options.memorySource {
+		repository = profile.NewOverlayRepository(options.memoryProfiles, repository)
+	}
+
+	return repository
+}
+
 func fileSource(name string) (fs.FS, string, error) {
 	cleanName := strings.TrimSpace(name)
 	if cleanName == "" {
@@ -482,7 +492,7 @@ func (e *Engine) InspectPrompt(
 // InspectProfile trims surrounding whitespace from profileID and looks up the
 // resulting nonblank ID exactly and case-sensitively through the engine's
 // ordinary in-memory, configured-source, and built-in profile precedence. It
-// applies framework defaults, the selected backend, and then the selected
+// applies the framework timeout baseline, selected backend, and then selected
 // profile to EffectiveModelParams without a request override. BackendID is
 // empty for an endpoint-only profile.
 //