fix(gemini): align thoughtSignature and stream tool IDs

pkg/providers/gemini_provider.go

@@ -226,7 +226,6 @@ func (p *GeminiProvider) buildRequestBody(
 				}
 				if thoughtSignature != "" {
 					part.ThoughtSignature = thoughtSignature
-					part.ThoughtSignatureSnake = thoughtSignature
 				}
 				content.Parts = append(content.Parts, part)
 			}
@@ -508,12 +507,25 @@ func parseGeminiStreamResponse(
 				}
 				if part.FunctionCall != nil {
 					tc := buildGeminiToolCall(part)
-					key := tc.ID
-					if strings.TrimSpace(key) == "" {
-						fallbackIndex++
-						key = fmt.Sprintf("%s#%d", tc.Name, fallbackIndex)
-						tc.ID = key
+					if strings.TrimSpace(tc.Name) == "" {
+						continue
 					}
+
+					key := strings.TrimSpace(part.FunctionCall.ID)
+					if key == "" {
+						if len(toolCallOrder) > 0 {
+							lastKey := toolCallOrder[len(toolCallOrder)-1]
+							if lastTC, exists := toolCallsByID[lastKey]; exists && lastTC.Name == tc.Name {
+								key = lastKey
+							}
+						}
+						if key == "" {
+							fallbackIndex++
+							key = fmt.Sprintf("%s#%d", tc.Name, fallbackIndex)
+						}
+					}
+
+					tc.ID = key
 					if _, exists := toolCallsByID[key]; !exists {
 						toolCallOrder = append(toolCallOrder, key)
 					}

pkg/providers/gemini_provider_test.go

@@ -289,6 +289,127 @@ func TestGeminiProvider_ChatStreamReturnsErrorOnInvalidDataFrame(t *testing.T) {
 	}
 }
 
+func TestGeminiProvider_BuildRequestBody_UsesCamelCaseThoughtSignatureOnly(t *testing.T) {
+	provider := NewGeminiProvider("test-key", "https://example.com/v1beta", "", "", 0, nil, nil)
+
+	body := provider.buildRequestBody(
+		[]Message{{
+			Role: "assistant",
+			ToolCalls: []ToolCall{{
+				ID:        "call_1",
+				Name:      "search",
+				Arguments: map[string]any{"q": "hello"},
+				Function: &FunctionCall{
+					Name:             "search",
+					Arguments:        `{"q":"hello"}`,
+					ThoughtSignature: "sig-1",
+				},
+			}},
+		}},
+		nil,
+		"gemini-2.5-flash",
+		nil,
+	)
+
+	raw, err := json.Marshal(body)
+	if err != nil {
+		t.Fatalf("marshal request body: %v", err)
+	}
+	jsonBody := string(raw)
+
+	if !strings.Contains(jsonBody, `"thoughtSignature":"sig-1"`) {
+		t.Fatalf("request body = %s, expected camelCase thoughtSignature", jsonBody)
+	}
+	if strings.Contains(jsonBody, `"thought_signature"`) {
+		t.Fatalf("request body = %s, unexpected snake_case thought_signature", jsonBody)
+	}
+}
+
+func TestGeminiProvider_ChatStreamCoalescesToolCallWithoutWireID(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		flusher, ok := w.(http.Flusher)
+		if !ok {
+			t.Fatal("response writer is not flushable")
+		}
+
+		chunks := []map[string]any{
+			{
+				"candidates": []any{map[string]any{
+					"content": map[string]any{
+						"parts": []any{
+							map[string]any{
+								"functionCall": map[string]any{
+									"name": "search",
+									"args": map[string]any{"q": "first"},
+								},
+							},
+						},
+					},
+				}},
+			},
+			{
+				"candidates": []any{map[string]any{
+					"content": map[string]any{
+						"parts": []any{
+							map[string]any{
+								"functionCall": map[string]any{
+									"name": "search",
+									"args": map[string]any{"q": "second"},
+								},
+							},
+						},
+					},
+					"finishReason": "STOP",
+				}},
+			},
+		}
+
+		for _, chunk := range chunks {
+			raw, err := json.Marshal(chunk)
+			if err != nil {
+				t.Fatalf("marshal chunk: %v", err)
+			}
+			if _, err := fmt.Fprintf(w, "data: %s\n\n", raw); err != nil {
+				t.Fatalf("write chunk: %v", err)
+			}
+			flusher.Flush()
+		}
+		_, _ = fmt.Fprint(w, "data: [DONE]\n\n")
+		flusher.Flush()
+	}))
+	defer server.Close()
+
+	provider := NewGeminiProvider("test-key", server.URL, "", "", 0, nil, nil)
+	resp, err := provider.ChatStream(
+		t.Context(),
+		[]Message{{Role: "user", Content: "hello"}},
+		nil,
+		"gemini-2.5-flash",
+		nil,
+		nil,
+	)
+	if err != nil {
+		t.Fatalf("ChatStream() error = %v", err)
+	}
+	if len(resp.ToolCalls) != 1 {
+		t.Fatalf("ToolCalls len = %d, want 1", len(resp.ToolCalls))
+	}
+	tc := resp.ToolCalls[0]
+	if tc.ID != "search#1" {
+		t.Fatalf("ToolCall ID = %q, want %q", tc.ID, "search#1")
+	}
+	if tc.Name != "search" {
+		t.Fatalf("ToolCall Name = %q, want %q", tc.Name, "search")
+	}
+	if argQ, ok := tc.Arguments["q"].(string); !ok || argQ != "second" {
+		t.Fatalf("ToolCall Arguments = %#v, want q=second", tc.Arguments)
+	}
+	if resp.FinishReason != "tool_calls" {
+		t.Fatalf("FinishReason = %q, want %q", resp.FinishReason, "tool_calls")
+	}
+}
+
 func TestGeminiProvider_BuildRequestBodyIncludesMediaAndThinkingConfig(t *testing.T) {
 	provider := NewGeminiProvider("test-key", "https://example.com/v1beta", "", "", 0, nil, nil)