fix(edge): Gemini 병렬 도구 인덱스를 정규화한다

apps/edge/internal/openai/provider_model_rewrite.go

@@ -510,9 +510,6 @@ func rewriteProviderJSONResponse(body []byte, model, toolCallWire string) []byte
 }
 
 func normalizeGeminiChatProviderResponse(body []byte) []byte {
-	if !bytes.Contains(body, []byte(`"thought_signature"`)) {
-		return body
-	}
 	decoder := json.NewDecoder(bytes.NewReader(body))
 	decoder.UseNumber()
 	var response map[string]any
@@ -530,11 +527,22 @@ func normalizeGeminiChatProviderResponse(body []byte) []byte {
 			if !ok {
 				continue
 			}
-			for _, rawCall := range anySlice(message["tool_calls"]) {
+			toolCalls := anySlice(message["tool_calls"])
+			for index, rawCall := range toolCalls {
 				call, ok := rawCall.(map[string]any)
 				if !ok {
 					continue
 				}
+				// Gemini's Chat-compatible stream may emit several complete tool
+				// calls in one delta without OpenAI's per-call index. Preserve their
+				// positional identity so the stream decoder does not concatenate
+				// independent argument objects into index zero.
+				if messageKey == "delta" && len(toolCalls) > 1 {
+					if _, present := call["index"]; !present {
+						call["index"] = index
+						changed = true
+					}
+				}
 				id, idOK := call["id"].(string)
 				extra, extraOK := call["extra_content"].(map[string]any)
 				if !idOK || id == "" || !extraOK {

apps/edge/internal/openai/provider_model_rewrite_test.go

@@ -76,6 +76,32 @@ func TestProviderThoughtSignatureNormalizationIsGeminiProfileOnly(t *testing.T)
 	}
 }
 
+func TestGeminiChatProviderResponseAddsMissingParallelToolIndices(t *testing.T) {
+	response := []byte(`{"id":"chat-1","choices":[{"delta":{"tool_calls":[{"id":"call-1","function":{"name":"read_file","arguments":"{\"path\":\"plan.md\"}"}},{"id":"call-2","function":{"name":"read_file","arguments":"{\"path\":\"review.md\"}"}},{"id":"call-3","function":{"name":"bash","arguments":"{\"command\":\"test -f index.html\"}"}}]}}]}`)
+	normalized := normalizeGeminiChatProviderResponse(response)
+	var body map[string]any
+	if err := json.Unmarshal(normalized, &body); err != nil {
+		t.Fatal(err)
+	}
+	choice := anySlice(body["choices"])[0].(map[string]any)
+	delta := choice["delta"].(map[string]any)
+	calls := anySlice(delta["tool_calls"])
+	for index, raw := range calls {
+		call := raw.(map[string]any)
+		if got := int(call["index"].(float64)); got != index {
+			t.Fatalf("tool call %d index = %d", index, got)
+		}
+	}
+
+	stage, err := decodeOpenAIPresetSSE([]byte("data: " + string(normalized) + "\n\ndata: {\"id\":\"chat-1\",\"choices\":[{\"delta\":{},\"finish_reason\":\"tool_calls\"}],\"usage\":{\"prompt_tokens\":1,\"completion_tokens\":1,\"total_tokens\":2}}\n\ndata: [DONE]\n\n"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(stage.ToolCalls) != 3 {
+		t.Fatalf("decoded tool calls = %+v", stage.ToolCalls)
+	}
+}
+
 func TestProviderChatTokenLimitNormalizationUsesSelectedProfile(t *testing.T) {
 	tests := []struct {
 		name       string