fix(clients): preserve gemini tool call responses

apps/api/internal/clients/clients_test.go

@@ -655,6 +655,63 @@ func TestGeminiClientChatRestoresToolContext(t *testing.T) {
 	}
 }
 
+func TestGeminiClientChatConvertsFunctionCallResponse(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"candidates": []any{map[string]any{
+				"finishReason": "STOP",
+				"content": map[string]any{"parts": []any{
+					map[string]any{"functionCall": map[string]any{
+						"name": "get_weather",
+						"args": map[string]any{"city": "SF"},
+					}},
+				}},
+			}},
+		})
+	}))
+	defer server.Close()
+
+	response, err := (GeminiClient{HTTPClient: server.Client()}).Run(context.Background(), Request{
+		Kind:  "chat.completions",
+		Model: "gemini:gemini-2.5-flash",
+		Body: map[string]any{
+			"model":    "gemini:gemini-2.5-flash",
+			"messages": []any{map[string]any{"role": "user", "content": "weather?"}},
+			"tools": []any{map[string]any{
+				"type":     "function",
+				"function": map[string]any{"name": "get_weather"},
+			}},
+		},
+		Candidate: store.RuntimeModelCandidate{
+			BaseURL:           server.URL,
+			ProviderModelName: "gemini-2.5-flash",
+			ModelType:         "chat",
+			Credentials:       map[string]any{"apiKey": "gemini-key"},
+		},
+	})
+	if err != nil {
+		t.Fatalf("run gemini client: %v", err)
+	}
+	choices, _ := response.Result["choices"].([]any)
+	choice, _ := choices[0].(map[string]any)
+	if choice["finish_reason"] != "tool_calls" {
+		t.Fatalf("Gemini function call should use tool_calls finish reason: %+v", response.Result)
+	}
+	message, _ := choice["message"].(map[string]any)
+	if message["content"] != nil {
+		t.Fatalf("tool-only Gemini response should keep nullable content: %+v", message)
+	}
+	toolCalls, _ := message["tool_calls"].([]any)
+	if len(toolCalls) != 1 {
+		t.Fatalf("Gemini function call was not converted: %+v", message)
+	}
+	toolCall, _ := toolCalls[0].(map[string]any)
+	function, _ := toolCall["function"].(map[string]any)
+	if toolCall["type"] != "function" || toolCall["id"] != "call_0" || function["name"] != "get_weather" || function["arguments"] != `{"city":"SF"}` {
+		t.Fatalf("unexpected Gemini tool call: %+v", toolCall)
+	}
+}
+
 func TestGeminiURLAcceptsVersionedBaseURL(t *testing.T) {
 	got := geminiURL("https://generativelanguage.googleapis.com/v1beta", "gemini-2.5-flash", "test-key")
 	want := "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent?key=test-key"

apps/api/internal/clients/gemini.go

@@ -265,7 +265,7 @@ func geminiResult(request Request, raw map[string]any) map[string]any {
 			"raw":     raw,
 		}
 	}
-	content := geminiText(raw)
+	message, finishReason := geminiChatMessage(raw)
 	return map[string]any{
 		"id":      "gemini-chat",
 		"object":  "chat.completion",
@@ -273,8 +273,8 @@ func geminiResult(request Request, raw map[string]any) map[string]any {
 		"model":   request.Model,
 		"choices": []any{map[string]any{
 			"index":         0,
-			"finish_reason": "stop",
+			"finish_reason": finishReason,
-			"message":       map[string]any{"role": "assistant", "content": content},
+			"message":       message,
 		}},
 		"usage": geminiUsageMap(raw),
 		"raw":   raw,
@@ -303,19 +303,59 @@ func textFromMessages(body map[string]any) string {
 }
 
 func geminiText(raw map[string]any) string {
+	message, _ := geminiChatMessage(raw)
+	content, _ := message["content"].(string)
+	return content
+}
+
+func geminiChatMessage(raw map[string]any) (map[string]any, string) {
 	candidates, _ := raw["candidates"].([]any)
 	for _, candidate := range candidates {
 		candidateMap, _ := candidate.(map[string]any)
 		content, _ := candidateMap["content"].(map[string]any)
 		parts, _ := content["parts"].([]any)
+		textParts := make([]string, 0, len(parts))
+		toolCalls := make([]any, 0)
 		for _, part := range parts {
 			partMap, _ := part.(map[string]any)
 			if text, ok := partMap["text"].(string); ok && text != "" {
-				return text
+				textParts = append(textParts, text)
+			}
+			functionCall := mapFromAny(firstPresent(partMap["functionCall"], partMap["function_call"]))
+			if len(functionCall) == 0 {
+				continue
+			}
+			if toolCall := normalizeGeminiFunctionCall(functionCall, len(toolCalls), false); toolCall != nil {
+				toolCalls = append(toolCalls, toolCall)
 			}
 		}
+		message := map[string]any{
+			"role":    "assistant",
+			"content": strings.Join(textParts, ""),
+		}
+		if len(toolCalls) > 0 {
+			message["tool_calls"] = toolCalls
+			if len(textParts) == 0 {
+				message["content"] = nil
+			}
+		}
+		return message, geminiFinishReason(candidateMap, len(toolCalls) > 0)
+	}
+	return map[string]any{"role": "assistant", "content": ""}, "stop"
+}
+
+func geminiFinishReason(candidate map[string]any, hasToolCalls bool) string {
+	if hasToolCalls {
+		return "tool_calls"
+	}
+	switch strings.ToUpper(stringFromAny(candidate["finishReason"])) {
+	case "MAX_TOKENS":
+		return "length"
+	case "SAFETY", "RECITATION", "BLOCKLIST", "PROHIBITED_CONTENT", "SPII":
+		return "content_filter"
+	default:
+		return "stop"
 	}
-	return ""
 }
 
 func geminiImageData(raw map[string]any) []any {