Add reasoning streaming

internal/service/service.go

@@ -585,6 +585,8 @@ type StreamMessage struct {
 	Error string `json:"error,omitempty"`
 	// Delta is a text fragment from the assistant response.
 	Delta string `json:"delta,omitempty"`
+	// ReasoningDelta is a reasoning text fragment from the assistant response.
+	ReasoningDelta string `json:"reasoning_delta,omitempty"`
 	// Message is the chat completion message.
 	Message *llm.Message `json:"message,omitempty"`
 	// Provider is the LLM provider used for the response.
@@ -709,9 +711,10 @@ func (svc *Service) chatStream(w http.ResponseWriter, r *http.Request) {
 	// Consume events and send as SSE.
 	for evt := range events {
 		msg := StreamMessage{
-			Delta:    evt.Delta,
-			Provider: provider,
-			Model:    model,
+			Delta:          evt.Delta,
+			ReasoningDelta: evt.ReasoningDelta,
+			Provider:       provider,
+			Model:          model,
 		}
 		if evt.Message.Role != "" {
 			msg.Message = &evt.Message