Implement a library profile API and built-in profile docs

engine.go

@@ -58,9 +58,11 @@ type engineOptions struct {
 	llmClient       llm.Client
 	promptDefs      promptdef.Repository
 	profiles        profile.Repository
+	memoryProfiles  profile.Repository
 	validator       validate.Validator
 	promptSource    bool
 	profileSource   bool
+	memorySource    bool
 	validatorSource bool
 }
 
@@ -127,6 +129,20 @@ func WithProfileFile(path string) Option {
 	}
 }
 
+// WithProfiles configures in-memory profiles that take precedence over
+// configured profile files and built-in profiles.
+func WithProfiles(profiles ...Profile) Option {
+	return func(options *engineOptions) error {
+		repo, err := newMemoryProfileRepository(profiles)
+		if err != nil {
+			return err
+		}
+		options.memoryProfiles = repo
+		options.memorySource = true
+		return nil
+	}
+}
+
 func WithSchemaFS(fsys fs.FS, root string) Option {
 	return func(options *engineOptions) error {
 		if fsys == nil {
@@ -178,6 +194,9 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 	if options.profileSource {
 		profiles = builtin.NewRepositoryWithPrimary(options.profiles)
 	}
+	if options.memorySource {
+		profiles = profile.NewOverlayRepository(options.memoryProfiles, profiles)
+	}
 
 	validator := options.validator
 	if !options.validatorSource {