fix(openai_compat): parse reasoning_content in streaming responses

pkg/providers/openai_compat/provider.go

@@ -419,6 +419,7 @@ func parseStreamResponse(
 	onChunk func(accumulated string),
 ) (*LLMResponse, error) {
 	var textContent strings.Builder
+	var reasoningContent strings.Builder
 	var finishReason string
 	var usage *UsageInfo
 
@@ -451,8 +452,9 @@ func parseStreamResponse(
 		var chunk struct {
 			Choices []struct {
 				Delta struct {
-					Content   string `json:"content"`
-					ToolCalls []struct {
+					Content          string `json:"content"`
+					ReasoningContent string `json:"reasoning_content"`
+					ToolCalls        []struct {
 						Index    int    `json:"index"`
 						ID       string `json:"id"`
 						Function *struct {
@@ -487,6 +489,9 @@ func parseStreamResponse(
 				onChunk(textContent.String())
 			}
 		}
+		if choice.Delta.ReasoningContent != "" {
+			reasoningContent.WriteString(choice.Delta.ReasoningContent)
+		}
 
 		// Accumulate tool call deltas
 		for _, tc := range choice.Delta.ToolCalls {
@@ -544,10 +549,11 @@ func parseStreamResponse(
 	}
 
 	return &LLMResponse{
-		Content:      textContent.String(),
-		ToolCalls:    toolCalls,
-		FinishReason: finishReason,
-		Usage:        usage,
+		Content:          textContent.String(),
+		ReasoningContent: reasoningContent.String(),
+		ToolCalls:        toolCalls,
+		FinishReason:     finishReason,
+		Usage:            usage,
 	}, nil
 }
 

pkg/providers/openai_compat/provider_test.go

@@ -1195,6 +1195,57 @@ func TestProviderChatStream_CustomHeadersInjected(t *testing.T) {
 	}
 }
 
+func TestProviderChatStream_ParsesReasoningContent(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(
+			"data: {\"choices\":[{\"delta\":{\"reasoning_content\":\"Let me \",\"content\":\"Checking \",\"tool_calls\":[{\"index\":0,\"id\":\"call_1\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"{\\\"city\\\":\"}}]}}]}\n\n",
+		))
+		_, _ = w.Write([]byte(
+			"data: {\"choices\":[{\"delta\":{\"reasoning_content\":\"think step by step.\",\"content\":\"the weather\",\"tool_calls\":[{\"index\":0,\"function\":{\"arguments\":\"\\\"Hangzhou\\\"}\"}}]},\"finish_reason\":\"tool_calls\"}],\"usage\":{\"prompt_tokens\":10,\"completion_tokens\":6,\"total_tokens\":16}}\n\n",
+		))
+		_, _ = w.Write([]byte("data: [DONE]\n\n"))
+	}))
+	defer server.Close()
+
+	p := NewProvider("key", server.URL, "")
+	out, err := p.ChatStream(
+		t.Context(),
+		[]Message{{Role: "user", Content: "weather?"}},
+		nil,
+		"deepseek-v4-flash",
+		nil,
+		nil,
+	)
+	if err != nil {
+		t.Fatalf("ChatStream() error = %v", err)
+	}
+	if out.Content != "Checking the weather" {
+		t.Fatalf("Content = %q, want %q", out.Content, "Checking the weather")
+	}
+	if out.ReasoningContent != "Let me think step by step." {
+		t.Fatalf("ReasoningContent = %q, want %q", out.ReasoningContent, "Let me think step by step.")
+	}
+	if len(out.ToolCalls) != 1 {
+		t.Fatalf("len(ToolCalls) = %d, want 1", len(out.ToolCalls))
+	}
+	if out.ToolCalls[0].ID != "call_1" {
+		t.Fatalf("ToolCalls[0].ID = %q, want %q", out.ToolCalls[0].ID, "call_1")
+	}
+	if out.ToolCalls[0].Name != "get_weather" {
+		t.Fatalf("ToolCalls[0].Name = %q, want %q", out.ToolCalls[0].Name, "get_weather")
+	}
+	if out.ToolCalls[0].Arguments["city"] != "Hangzhou" {
+		t.Fatalf("ToolCalls[0].Arguments[city] = %v, want %q", out.ToolCalls[0].Arguments["city"], "Hangzhou")
+	}
+	if out.FinishReason != "tool_calls" {
+		t.Fatalf("FinishReason = %q, want %q", out.FinishReason, "tool_calls")
+	}
+	if out.Usage == nil || out.Usage.TotalTokens != 16 {
+		t.Fatalf("Usage = %#v, want total tokens 16", out.Usage)
+	}
+}
+
 type roundTripperFunc func(*http.Request) (*http.Response, error)
 
 func (f roundTripperFunc) RoundTrip(r *http.Request) (*http.Response, error) {