fix: preserve reasoning_content for OpenAI-compatible reasoning models

pkg/agent/loop.go

@@ -622,8 +622,9 @@ func (al *AgentLoop) runLLMIteration(
 
 		// Build assistant message with tool calls
 		assistantMsg := providers.Message{
-			Role:    "assistant",
-			Content: response.Content,
+			Role:             "assistant",
+			Content:          response.Content,
+			ReasoningContent: response.ReasoningContent,
 		}
 		for _, tc := range normalizedToolCalls {
 			argumentsJSON, _ := json.Marshal(tc.Arguments)

pkg/providers/openai_compat/provider.go

@@ -148,8 +148,9 @@ func parseResponse(body []byte) (*LLMResponse, error) {
 	var apiResponse struct {
 		Choices []struct {
 			Message struct {
-				Content   string `json:"content"`
-				ToolCalls []struct {
+				Content          string `json:"content"`
+				ReasoningContent string `json:"reasoning_content"`
+				ToolCalls        []struct {
 					ID       string `json:"id"`
 					Type     string `json:"type"`
 					Function *struct {
@@ -221,10 +222,11 @@ func parseResponse(body []byte) (*LLMResponse, error) {
 	}
 
 	return &LLMResponse{
-		Content:      choice.Message.Content,
-		ToolCalls:    toolCalls,
-		FinishReason: choice.FinishReason,
-		Usage:        apiResponse.Usage,
+		Content:          choice.Message.Content,
+		ReasoningContent: choice.Message.ReasoningContent,
+		ToolCalls:        toolCalls,
+		FinishReason:     choice.FinishReason,
+		Usage:            apiResponse.Usage,
 	}, nil
 }
 

pkg/providers/openai_compat/provider_test.go

@@ -101,6 +101,50 @@ func TestProviderChat_ParsesToolCalls(t *testing.T) {
 	}
 }
 
+func TestProviderChat_ParsesReasoningContent(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := map[string]any{
+			"choices": []map[string]any{
+				{
+					"message": map[string]any{
+						"content":           "The answer is 2",
+						"reasoning_content": "Let me think step by step... 1+1=2",
+						"tool_calls": []map[string]any{
+							{
+								"id":   "call_1",
+								"type": "function",
+								"function": map[string]any{
+									"name":      "calculator",
+									"arguments": "{\"expr\":\"1+1\"}",
+								},
+							},
+						},
+					},
+					"finish_reason": "tool_calls",
+				},
+			},
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	p := NewProvider("key", server.URL, "")
+	out, err := p.Chat(t.Context(), []Message{{Role: "user", Content: "1+1=?"}}, nil, "kimi-k2.5", nil)
+	if err != nil {
+		t.Fatalf("Chat() error = %v", err)
+	}
+	if out.ReasoningContent != "Let me think step by step... 1+1=2" {
+		t.Fatalf("ReasoningContent = %q, want %q", out.ReasoningContent, "Let me think step by step... 1+1=2")
+	}
+	if out.Content != "The answer is 2" {
+		t.Fatalf("Content = %q, want %q", out.Content, "The answer is 2")
+	}
+	if len(out.ToolCalls) != 1 {
+		t.Fatalf("len(ToolCalls) = %d, want 1", len(out.ToolCalls))
+	}
+}
+
 func TestProviderChat_HTTPError(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "bad request", http.StatusBadRequest)

pkg/providers/protocoltypes/types.go

@@ -25,10 +25,11 @@ type FunctionCall struct {
 }
 
 type LLMResponse struct {
-	Content      string     `json:"content"`
-	ToolCalls    []ToolCall `json:"tool_calls,omitempty"`
-	FinishReason string     `json:"finish_reason"`
-	Usage        *UsageInfo `json:"usage,omitempty"`
+	Content          string     `json:"content"`
+	ReasoningContent string     `json:"reasoning_content,omitempty"`
+	ToolCalls        []ToolCall `json:"tool_calls,omitempty"`
+	FinishReason     string     `json:"finish_reason"`
+	Usage            *UsageInfo `json:"usage,omitempty"`
 }
 
 type UsageInfo struct {
@@ -38,10 +39,11 @@ type UsageInfo struct {
 }
 
 type Message struct {
-	Role       string     `json:"role"`
-	Content    string     `json:"content"`
-	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
-	ToolCallID string     `json:"tool_call_id,omitempty"`
+	Role             string     `json:"role"`
+	Content          string     `json:"content"`
+	ReasoningContent string     `json:"reasoning_content,omitempty"`
+	ToolCalls        []ToolCall `json:"tool_calls,omitempty"`
+	ToolCallID       string     `json:"tool_call_id,omitempty"`
 }
 
 type ToolDefinition struct {