Enable streaming UI updates for chat responses

internal/chat/service.go

@@ -18,6 +18,7 @@ const defaultSessionPrefix = "session-"
 // CompletionClient defines the subset of the OpenAI client used by the chat service.
 type CompletionClient interface {
 	CreateChatCompletion(ctx context.Context, req openai.ChatCompletionRequest) (*openai.ChatCompletionResponse, error)
+	StreamChatCompletion(ctx context.Context, req openai.ChatCompletionRequest, handler openai.ChatCompletionStreamHandler) (*openai.ChatCompletionResponse, error)
 }
 
 // MessageRepository defines persistence hooks used by the chat service.
@@ -67,8 +68,9 @@ func NewService(logger *slog.Logger, modelCfg config.ModelConfig, client Complet
 	}, nil
 }
 
-// Send submits a user message and returns the assistant reply.
-func (s *Service) Send(ctx context.Context, input string) (string, error) {
+// Send submits a user message and returns the assistant reply. When streamHandler is provided and streaming is enabled,
+// partial responses are forwarded to the handler as they arrive.
+func (s *Service) Send(ctx context.Context, input string, streamHandler openai.ChatCompletionStreamHandler) (string, error) {
 	if s == nil {
 		return "", errors.New("service is nil")
 	}
@@ -99,7 +101,13 @@ func (s *Service) Send(ctx context.Context, input string) (string, error) {
 
 	s.logger.DebugContext(ctx, "sending chat completion", "model", s.model, "message_count", len(messages))
 
-	resp, err := s.client.CreateChatCompletion(ctx, req)
+	var resp *openai.ChatCompletionResponse
+	var err error
+	if s.stream {
+		resp, err = s.client.StreamChatCompletion(ctx, req, streamHandler)
+	} else {
+		resp, err = s.client.CreateChatCompletion(ctx, req)
+	}
 	if err != nil {
 		return "", err
 	}
@@ -127,6 +135,14 @@ func (s *Service) History() []openai.ChatMessage {
 	return historyCopy
 }
 
+// StreamingEnabled reports whether streaming completions are configured for this service.
+func (s *Service) StreamingEnabled() bool {
+	if s == nil {
+		return false
+	}
+	return s.stream
+}
+
 // Reset clears the in-memory conversation history.
 func (s *Service) Reset() {
 	if s == nil {