diff --git a/relay/channel/deepseek/adaptor.go b/relay/channel/deepseek/adaptor.go
index e6cc00e..ce6752d 100644
--- a/relay/channel/deepseek/adaptor.go
+++ b/relay/channel/deepseek/adaptor.go
@@ -38,6 +38,12 @@ func (a *Adaptor) GetRequestURL(info *common.RelayInfo) (string, error) {
 		}
 		return betaURL + "/completions", nil
 	case constant.RelayModeChatCompletions:
+		// chat_via_responses 桥接：请求体已由 relaykit 转成 Responses 格式，URL 必须同步
+		// 切到 /v1/responses——否则 Responses 体打到 chat 端点，上游按 chat 格式反序列化
+		// 直接 400（tools[0] missing field `function`）
+		if info.UseResponsesAPI {
+			return baseURL + "/v1/responses", nil
+		}
 		return baseURL + "/v1/chat/completions", nil
 	case constant.RelayModeClaudeMessages:
 		return baseURL + "/anthropic/v1/messages", nil
diff --git a/relay/channel/deepseek/adaptor_test.go b/relay/channel/deepseek/adaptor_test.go
index e72222a..8364fce 100644
--- a/relay/channel/deepseek/adaptor_test.go
+++ b/relay/channel/deepseek/adaptor_test.go
@@ -59,6 +59,38 @@ func TestGetRequestURL_ResponsesFlagRouting(t *testing.T) {
 	}
 }
 
+// TestGetRequestURL_ChatViaResponsesBridge chat 入站 + chat_via_responses 桥接：
+// 请求体已被 relaykit 转成 Responses 格式，URL 必须同步切到 /v1/responses——
+// 回归 chn_debug_logs #356：URL 不切时 Responses 体打到 chat 端点，
+// 上游 400 "tools[0]: missing field `function`"。
+func TestGetRequestURL_ChatViaResponsesBridge(t *testing.T) {
+	a := &Adaptor{}
+	info := deepseekResponsesInfo(false)
+	info.RelayMode = int(constant.RelayModeChatCompletions)
+	info.InboundFormat = constant.RelayFormatOpenAI
+	info.ClientFormat = constant.RelayFormatOpenAI
+	info.ChannelMeta.ChatViaResponses = true
+	info.UseResponsesAPI = true
+
+	got, err := a.GetRequestURL(info)
+	if err != nil {
+		t.Fatalf("GetRequestURL error: %v", err)
+	}
+	if want := "https://api.deepseek.example.com/v1/responses"; got != want {
+		t.Errorf("chat via responses bridge: URL = %q, want %q", got, want)
+	}
+
+	// 未开桥接的 chat 请求仍走 chat 端点
+	info.UseResponsesAPI = false
+	got, err = a.GetRequestURL(info)
+	if err != nil {
+		t.Fatalf("GetRequestURL error: %v", err)
+	}
+	if want := "https://api.deepseek.example.com/v1/chat/completions"; got != want {
+		t.Errorf("plain chat: URL = %q, want %q", got, want)
+	}
+}
+
 const deepseekResponsesRequestBody = `{"model":"deepseek-v4-flash","instructions":"You are helpful.","input":[{"type":"message","role":"user","content":[{"type":"input_text","text":"你好"}]}],"stream":true}`
 
 // TestConvertRequest_ResponsesChatFallback_HardFail chat-only 上游的 Responses→chat
diff --git a/relay/channel/openai/converter.go b/relay/channel/openai/converter.go
index 4aa81e0..f10bcb2 100644
--- a/relay/channel/openai/converter.go
+++ b/relay/channel/openai/converter.go
@@ -1134,6 +1134,10 @@ func HandleResponsesStreamToChat(ctx context.Context, resp *http.Response, info
 	toolCallNameByID := make(map[string]string)
 	toolCallArgsByID := make(map[string]string)
 	toolCallNameSent := make(map[string]bool)
+	// item_id → call_id 映射：function_call 项的 item.id（OpenAI 为 fc_xxx、DeepSeek 为 UUID）
+	// 与 call_id 是两个不同的值，而 arguments 增量事件只带 item_id。不做映射会把同一
+	// 工具调用拆成两个 index，客户端在无 name 的新 index 上报错
+	callIDByItemID := make(map[string]string)
 
 	sendChatChunk := func(chunk *dto.ChatCompletionStreamResponse) bool {
 		if chunk == nil {
@@ -1226,6 +1230,9 @@ func HandleResponsesStreamToChat(ctx context.Context, resp *http.Response, info
 			if callID == "" {
 				return
 			}
+			if itemID := strings.TrimSpace(streamResp.Item.ID); itemID != "" {
+				callIDByItemID[itemID] = callID
+			}
 			name := strings.TrimSpace(streamResp.Item.Name)
 			if name != "" {
 				toolCallNameByID[callID] = name
@@ -1251,10 +1258,14 @@ func HandleResponsesStreamToChat(ctx context.Context, resp *http.Response, info
 
 		case "response.function_call_arguments.delta":
 			itemID := strings.TrimSpace(streamResp.ItemID)
-			callID := itemID
-			if callID == "" {
+			if itemID == "" {
 				return
 			}
+			// 增量事件只带 item_id，先映射回 call_id（无 added 事件先行的上游按原值兜底）
+			callID := callIDByItemID[itemID]
+			if callID == "" {
+				callID = itemID
+			}
 			toolCallArgsByID[callID] += streamResp.Delta
 			if !r2cSendToolCallChunk(responseID, createAt, model, callID, "", streamResp.Delta, toolCallIndexByID, toolCallNameByID, toolCallNameSent, writer, sendChatChunk) {
 				sr.Stop(fmt.Errorf("send tool call args chunk failed"))
diff --git a/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream.go b/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream.go
index 61eb086..5f29b7e 100644
--- a/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream.go
+++ b/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream.go
@@ -70,6 +70,10 @@ func (c *ResponsesToOpenAIStreamConverter) ConvertStreamResponse(
 	toolCallNameByID := make(map[string]string)
 	toolCallArgsByID := make(map[string]string)
 	toolCallNameSent := make(map[string]bool)
+	// item_id → call_id 映射：function_call 项的 item.id（OpenAI 为 fc_xxx、DeepSeek 为 UUID）
+	// 与 call_id 是两个不同的值，而 arguments 增量事件只带 item_id。不做映射会把同一
+	// 工具调用拆成两个 index，客户端在无 name 的新 index 上报错
+	callIDByItemID := make(map[string]string)
 
 	sendStartIfNeeded := func() error {
 		if sentStart {
@@ -172,6 +176,9 @@ func (c *ResponsesToOpenAIStreamConverter) ConvertStreamResponse(
 			if callID == "" {
 				continue
 			}
+			if itemID := strings.TrimSpace(streamResp.Item.ID); itemID != "" {
+				callIDByItemID[itemID] = callID
+			}
 			name := strings.TrimSpace(streamResp.Item.Name)
 			if name != "" {
 				toolCallNameByID[callID] = name
@@ -196,10 +203,15 @@ func (c *ResponsesToOpenAIStreamConverter) ConvertStreamResponse(
 			usageText.WriteString(argsDelta)
 
 		case "response.function_call_arguments.delta":
-			callID := strings.TrimSpace(streamResp.ItemID)
-			if callID == "" {
+			itemID := strings.TrimSpace(streamResp.ItemID)
+			if itemID == "" {
 				continue
 			}
+			// 增量事件只带 item_id，先映射回 call_id（无 added 事件先行的上游按原值兜底）
+			callID := callIDByItemID[itemID]
+			if callID == "" {
+				callID = itemID
+			}
 			toolCallArgsByID[callID] += streamResp.Delta
 			if err := sendToolCallChunk(chunkWriter, responseID, createAt, model, callID, "", streamResp.Delta, toolCallIndexByID, toolCallNameByID, toolCallNameSent); err != nil {
 				return fmt.Errorf("send tool call args chunk failed: %w", err)
diff --git a/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream_test.go b/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream_test.go
index 4a20de5..ac865e8 100644
--- a/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream_test.go
+++ b/relaykit/relayconvert/internal/oai_responses/responses_to_openai_stream_test.go
@@ -141,6 +141,53 @@ func TestResponsesToOpenAIStream_ToolCalls(t *testing.T) {
 	}
 }
 
+// TestResponsesToOpenAIStream_ToolCallItemIDDiffersFromCallID 复现线上 bug（chn_debug_logs #357）：
+// function_call 项的 item.id（OpenAI 为 fc_xxx、DeepSeek 为 UUID）与 call_id 是两个不同的值，
+// 而 arguments 增量事件只带 item_id。不做 item_id→call_id 映射会把同一工具调用拆成两个
+// index（续块无 name），ai-sdk 客户端报 "Expected 'function.name' to be a string"。
+func TestResponsesToOpenAIStream_ToolCallItemIDDiffersFromCallID(t *testing.T) {
+	sse := strings.Join([]string{
+		`data: {"type":"response.output_item.added","output_index":0,"item":{"type":"function_call","id":"9abf972b-39ee-431d-b452-1aedef3f6762","call_id":"call_00_abc","name":"Bash","arguments":""}}`,
+		``,
+		`data: {"type":"response.function_call_arguments.delta","item_id":"9abf972b-39ee-431d-b452-1aedef3f6762","output_index":0,"delta":"{\"cmd\":"}`,
+		``,
+		`data: {"type":"response.function_call_arguments.delta","item_id":"9abf972b-39ee-431d-b452-1aedef3f6762","output_index":0,"delta":"\"ls\"}"}`,
+		``,
+		`data: {"type":"response.output_item.done","output_index":0,"item":{"type":"function_call","id":"9abf972b-39ee-431d-b452-1aedef3f6762","call_id":"call_00_abc","name":"Bash","arguments":"{\"cmd\":\"ls\"}"}}`,
+		``,
+		`data: {"type":"response.completed","response":{"id":"resp_up","object":"response","created_at":123,"status":"completed","usage":{"input_tokens":7,"output_tokens":3,"total_tokens":10}}}`,
+		``,
+		`data: [DONE]`,
+		``,
+	}, "\n")
+
+	chunks, err := runResponsesToChatStream(t, &convmeta.Values{OriginModelName: "gpt-4o"}, sse)
+	if err != nil {
+		t.Fatalf("ConvertStreamResponse: %v", err)
+	}
+
+	var args strings.Builder
+	for _, c := range chunks {
+		if len(c.Choices) == 0 {
+			continue
+		}
+		for _, tc := range c.Choices[0].Delta.ToolCalls {
+			// 所有分片必须归并到同一个调用：index 恒 0、id 恒为 call_id
+			if tc.Index == nil || *tc.Index != 0 {
+				t.Errorf("tool call index = %v, want 0（同一调用被拆成多个 index）", tc.Index)
+			}
+			if tc.ID != "" && tc.ID != "call_00_abc" {
+				t.Errorf("tool call id = %q, want call_00_abc（item_id 泄漏成了调用 id）", tc.ID)
+			}
+			args.WriteString(tc.Function.Arguments)
+		}
+	}
+	// output_item.done 的累计 arguments 与已发增量做差，不得重复下发
+	if args.String() != `{"cmd":"ls"}` {
+		t.Errorf("聚合 arguments = %q, want {\"cmd\":\"ls\"}", args.String())
+	}
+}
+
 // TestResponsesToOpenAIStream_ReasoningDelta 推理摘要 delta 转 reasoning_content。
 func TestResponsesToOpenAIStream_ReasoningDelta(t *testing.T) {
 	sse := strings.Join([]string{