diff --git a/DEPLOY.en.md b/DEPLOY.en.md
index 523c098..2d88c27 100644
--- a/DEPLOY.en.md
+++ b/DEPLOY.en.md
@@ -71,6 +71,7 @@ Notes:
 - `api/chat-stream.js` automatically falls back to the Go entry for non-stream requests or requests with `tools` (internal `__go=1`)
 - `api/chat-stream.js` is data-path only (stream relay + SSE conversion); auth/account/session/PoW preparation still comes from an internal Go prepare endpoint (enabled on Vercel only)
 - Go prepare creates a stream lease and Node releases it when streaming ends, keeping account occupancy semantics aligned with native Go streaming
+- `vercel.json` sets `maxDuration: 300` for both `api/chat-stream.js` and `api/index.go` (subject to your Vercel plan limits)
 
 Minimum environment variables:
 
diff --git a/DEPLOY.md b/DEPLOY.md
index 48e44b0..cb2c7b5 100644
--- a/DEPLOY.md
+++ b/DEPLOY.md
@@ -71,6 +71,7 @@ docker-compose up -d --build
 - `api/chat-stream.js` 对非流式请求或 `tools` 请求会自动回退到 Go 入口（内部 `__go=1`）
 - `api/chat-stream.js` 仅负责流式数据转发与 SSE 转换；鉴权、账号选择、会话创建、PoW 计算仍由 Go 内部 prepare 接口完成（仅 Vercel 启用）
 - Go prepare 会创建流式 lease，Node 在流结束后回调 release；账号占用语义与 Go 原生流式保持一致
+- `vercel.json` 已将 `api/chat-stream.js` 与 `api/index.go` 的 `maxDuration` 设为 `300`（受套餐上限约束）
 
 至少配置环境变量：
 
diff --git a/README.MD b/README.MD
index cc6e0b7..d21854a 100644
--- a/README.MD
+++ b/README.MD
@@ -90,6 +90,7 @@ docker-compose logs -f
 - `/v1/chat/completions` 在 Vercel 上默认走 `api/chat-stream.js`（Node Runtime）以保证实时 SSE
 - `api/chat-stream.js` 仅负责流式数据转发；鉴权、账号选择、会话/PoW 准备仍由 Go 内部 prepare 接口处理
 - Go prepare 会下发 `lease_id`，Node 在流结束后调用 release，确保账号占用时长与 Go 原生流式一致
+- WebUI 的“非流式测试”会直接请求 `?__go=1`，避免 Vercel 上 Node 中转导致长请求更易超时
 - 至少配置：
 - `DS2API_ADMIN_KEY`
 - `DS2API_CONFIG_JSON`（JSON 字符串或 Base64）
diff --git a/README.en.md b/README.en.md
index b84cbfc..26e82fb 100644
--- a/README.en.md
+++ b/README.en.md
@@ -90,6 +90,7 @@ docker-compose logs -f
 - `/v1/chat/completions` is routed to `api/chat-stream.js` (Node Runtime) on Vercel to preserve real-time SSE
 - `api/chat-stream.js` is data-path only; auth/account/session/PoW preparation still comes from an internal Go prepare endpoint
 - Go prepare returns a `lease_id`; Node releases it at stream end so account occupancy duration stays aligned with native Go streaming behavior
+- WebUI non-stream test calls `?__go=1` directly to avoid extra Node hop timeout risk on long Vercel requests
 - Minimum env vars:
 - `DS2API_ADMIN_KEY`
 - `DS2API_CONFIG_JSON` (raw JSON or Base64)
diff --git a/api/chat-stream.js b/api/chat-stream.js
index 8ea21fe..8879a47 100644
--- a/api/chat-stream.js
+++ b/api/chat-stream.js
@@ -1,5 +1,7 @@
 'use strict';
 
+const crypto = require('crypto');
+
 const DEEPSEEK_COMPLETION_URL = 'https://chat.deepseek.com/api/v0/chat/completion';
 
 const BASE_HEADERS = {
@@ -37,6 +39,14 @@ module.exports = async function handler(req, res) {
   }
 
   const rawBody = await readRawBody(req);
+
+  // Hard guard: only use Node data path for streaming on Vercel runtime.
+  // Any non-Vercel runtime always falls back to Go for full behavior parity.
+  if (!isVercelRuntime()) {
+    await proxyToGo(req, res, rawBody);
+    return;
+  }
+
   let payload;
   try {
     payload = JSON.parse(rawBody.toString('utf8') || '{}');
@@ -66,6 +76,7 @@ module.exports = async function handler(req, res) {
   const finalPrompt = asString(prep.body.final_prompt);
   const thinkingEnabled = toBool(prep.body.thinking_enabled);
   const searchEnabled = toBool(prep.body.search_enabled);
+  const toolNames = extractToolNames(payload.tools);
 
   if (!model || !leaseID || !deepseekToken || !powHeader || !completionPayload) {
     writeOpenAIError(res, 500, 'invalid vercel prepare response');
@@ -103,6 +114,9 @@ module.exports = async function handler(req, res) {
     let currentType = thinkingEnabled ? 'thinking' : 'text';
     let thinkingText = '';
     let outputText = '';
+    const toolSieveEnabled = toolNames.length > 0;
+    const toolSieveState = createToolSieveState();
+    let toolCallsEmitted = false;
     const decoder = new TextDecoder();
     const reader = completionRes.body.getReader();
     let buffered = '';
@@ -115,11 +129,42 @@ module.exports = async function handler(req, res) {
       }
     };
 
+    const sendDeltaFrame = (delta) => {
+      const payloadDelta = { ...delta };
+      if (!firstChunkSent) {
+        payloadDelta.role = 'assistant';
+        firstChunkSent = true;
+      }
+      sendFrame({
+        id: sessionID,
+        object: 'chat.completion.chunk',
+        created,
+        model,
+        choices: [{ delta: payloadDelta, index: 0 }],
+      });
+    };
+
     const finish = async (reason) => {
       if (ended) {
         return;
       }
       ended = true;
+      if (toolSieveEnabled) {
+        const tailEvents = flushToolSieve(toolSieveState, toolNames);
+        for (const evt of tailEvents) {
+          if (evt.type === 'tool_calls') {
+            toolCallsEmitted = true;
+            sendDeltaFrame({ tool_calls: formatOpenAIStreamToolCalls(evt.calls) });
+            continue;
+          }
+          if (evt.text) {
+            sendDeltaFrame({ content: evt.text });
+          }
+        }
+      }
+      if (toolCallsEmitted) {
+        reason = 'tool_calls';
+      }
       sendFrame({
         id: sessionID,
         object: 'chat.completion.chunk',
@@ -181,25 +226,27 @@ module.exports = async function handler(req, res) {
             if (searchEnabled && isCitation(p.text)) {
               continue;
             }
-            const delta = {};
-            if (!firstChunkSent) {
-              delta.role = 'assistant';
-              firstChunkSent = true;
-            }
             if (p.type === 'thinking') {
               thinkingText += p.text;
-              delta.reasoning_content = p.text;
+              sendDeltaFrame({ reasoning_content: p.text });
             } else {
               outputText += p.text;
-              delta.content = p.text;
+              if (!toolSieveEnabled) {
+                sendDeltaFrame({ content: p.text });
+                continue;
+              }
+              const events = processToolSieveChunk(toolSieveState, p.text, toolNames);
+              for (const evt of events) {
+                if (evt.type === 'tool_calls') {
+                  toolCallsEmitted = true;
+                  sendDeltaFrame({ tool_calls: formatOpenAIStreamToolCalls(evt.calls) });
+                  continue;
+                }
+                if (evt.text) {
+                  sendDeltaFrame({ content: evt.text });
+                }
+              }
             }
-            sendFrame({
-              id: sessionID,
-              object: 'chat.completion.chunk',
-              created,
-              model,
-              choices: [{ delta, index: 0 }],
-            });
           }
         }
       }
@@ -612,6 +659,10 @@ function toBool(v) {
   return v === true;
 }
 
+function isVercelRuntime() {
+  return asString(process.env.VERCEL) !== '' || asString(process.env.NOW_REGION) !== '';
+}
+
 function asString(v) {
   if (typeof v === 'string') {
     return v.trim();
@@ -624,3 +675,412 @@ function asString(v) {
   }
   return String(v).trim();
 }
+
+function extractToolNames(tools) {
+  if (!Array.isArray(tools) || tools.length === 0) {
+    return [];
+  }
+  const out = [];
+  for (const t of tools) {
+    if (!t || typeof t !== 'object') {
+      continue;
+    }
+    const fn = t.function && typeof t.function === 'object' ? t.function : t;
+    const name = asString(fn.name);
+    if (name) {
+      out.push(name);
+    }
+  }
+  return out;
+}
+
+function createToolSieveState() {
+  return {
+    pending: '',
+    capture: '',
+    capturing: false,
+  };
+}
+
+function processToolSieveChunk(state, chunk, toolNames) {
+  if (!state) {
+    return [];
+  }
+  if (chunk) {
+    state.pending += chunk;
+  }
+  const events = [];
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    if (state.capturing) {
+      if (state.pending) {
+        state.capture += state.pending;
+        state.pending = '';
+      }
+      const consumed = consumeToolCapture(state.capture, toolNames);
+      if (!consumed.ready) {
+        break;
+      }
+      state.capture = '';
+      state.capturing = false;
+      if (consumed.prefix) {
+        events.push({ type: 'text', text: consumed.prefix });
+      }
+      if (Array.isArray(consumed.calls) && consumed.calls.length > 0) {
+        events.push({ type: 'tool_calls', calls: consumed.calls });
+      }
+      if (consumed.suffix) {
+        state.pending += consumed.suffix;
+      }
+      continue;
+    }
+
+    if (!state.pending) {
+      break;
+    }
+
+    const start = findToolSegmentStart(state.pending);
+    if (start >= 0) {
+      const prefix = state.pending.slice(0, start);
+      if (prefix) {
+        events.push({ type: 'text', text: prefix });
+      }
+      state.capture = state.pending.slice(start);
+      state.pending = '';
+      state.capturing = true;
+      continue;
+    }
+
+    const [safe, hold] = splitSafeContent(state.pending, 64);
+    if (!safe) {
+      break;
+    }
+    state.pending = hold;
+    events.push({ type: 'text', text: safe });
+  }
+  return events;
+}
+
+function flushToolSieve(state, toolNames) {
+  if (!state) {
+    return [];
+  }
+  const events = processToolSieveChunk(state, '', toolNames);
+  if (state.capturing) {
+    const consumed = consumeToolCapture(state.capture, toolNames);
+    if (consumed.ready) {
+      if (consumed.prefix) {
+        events.push({ type: 'text', text: consumed.prefix });
+      }
+      if (Array.isArray(consumed.calls) && consumed.calls.length > 0) {
+        events.push({ type: 'tool_calls', calls: consumed.calls });
+      }
+      if (consumed.suffix) {
+        events.push({ type: 'text', text: consumed.suffix });
+      }
+    } else if (state.capture) {
+      events.push({ type: 'text', text: state.capture });
+    }
+    state.capture = '';
+    state.capturing = false;
+  }
+  if (state.pending) {
+    events.push({ type: 'text', text: state.pending });
+    state.pending = '';
+  }
+  return events;
+}
+
+function splitSafeContent(s, holdChars) {
+  const chars = Array.from(s || '');
+  if (chars.length <= holdChars) {
+    return ['', s];
+  }
+  return [chars.slice(0, chars.length - holdChars).join(''), chars.slice(chars.length - holdChars).join('')];
+}
+
+function findToolSegmentStart(s) {
+  if (!s) {
+    return -1;
+  }
+  const lower = s.toLowerCase();
+  const keyIdx = lower.indexOf('tool_calls');
+  if (keyIdx < 0) {
+    return -1;
+  }
+  const start = s.slice(0, keyIdx).lastIndexOf('{');
+  return start >= 0 ? start : keyIdx;
+}
+
+function consumeToolCapture(captured, toolNames) {
+  if (!captured) {
+    return { ready: false, prefix: '', calls: [], suffix: '' };
+  }
+  const lower = captured.toLowerCase();
+  const keyIdx = lower.indexOf('tool_calls');
+  if (keyIdx < 0) {
+    if (Array.from(captured).length >= 256) {
+      return { ready: true, prefix: captured, calls: [], suffix: '' };
+    }
+    return { ready: false, prefix: '', calls: [], suffix: '' };
+  }
+  const start = captured.slice(0, keyIdx).lastIndexOf('{');
+  if (start < 0) {
+    if (Array.from(captured).length >= 512) {
+      return { ready: true, prefix: captured, calls: [], suffix: '' };
+    }
+    return { ready: false, prefix: '', calls: [], suffix: '' };
+  }
+  const obj = extractJSONObjectFrom(captured, start);
+  if (!obj.ok) {
+    if (Array.from(captured).length >= 4096) {
+      return { ready: true, prefix: captured, calls: [], suffix: '' };
+    }
+    return { ready: false, prefix: '', calls: [], suffix: '' };
+  }
+  const parsed = parseToolCalls(captured.slice(start, obj.end), toolNames);
+  if (parsed.length === 0) {
+    return {
+      ready: true,
+      prefix: captured.slice(0, obj.end),
+      calls: [],
+      suffix: captured.slice(obj.end),
+    };
+  }
+  return {
+    ready: true,
+    prefix: captured.slice(0, start),
+    calls: parsed,
+    suffix: captured.slice(obj.end),
+  };
+}
+
+function extractJSONObjectFrom(text, start) {
+  if (!text || start < 0 || start >= text.length || text[start] !== '{') {
+    return { ok: false, end: 0 };
+  }
+  let depth = 0;
+  let quote = '';
+  let escaped = false;
+  for (let i = start; i < text.length; i += 1) {
+    const ch = text[i];
+    if (quote) {
+      if (escaped) {
+        escaped = false;
+        continue;
+      }
+      if (ch === '\\') {
+        escaped = true;
+        continue;
+      }
+      if (ch === quote) {
+        quote = '';
+      }
+      continue;
+    }
+    if (ch === '"' || ch === "'") {
+      quote = ch;
+      continue;
+    }
+    if (ch === '{') {
+      depth += 1;
+      continue;
+    }
+    if (ch === '}') {
+      depth -= 1;
+      if (depth === 0) {
+        return { ok: true, end: i + 1 };
+      }
+    }
+  }
+  return { ok: false, end: 0 };
+}
+
+function parseToolCalls(text, toolNames) {
+  if (!asString(text)) {
+    return [];
+  }
+  const candidates = buildToolCallCandidates(text);
+  let parsed = [];
+  for (const c of candidates) {
+    parsed = parseToolCallsPayload(c);
+    if (parsed.length > 0) {
+      break;
+    }
+  }
+  if (parsed.length === 0) {
+    return [];
+  }
+  const allowed = new Set((toolNames || []).filter(Boolean));
+  const out = [];
+  for (const tc of parsed) {
+    if (!tc || !tc.name) {
+      continue;
+    }
+    if (allowed.size > 0 && !allowed.has(tc.name)) {
+      continue;
+    }
+    out.push({ name: tc.name, input: tc.input || {} });
+  }
+  if (out.length === 0 && parsed.length > 0) {
+    for (const tc of parsed) {
+      if (!tc || !tc.name) {
+        continue;
+      }
+      out.push({ name: tc.name, input: tc.input || {} });
+    }
+  }
+  return out;
+}
+
+function buildToolCallCandidates(text) {
+  const trimmed = asString(text);
+  const candidates = [trimmed];
+  const fenced = trimmed.match(/```(?:json)?\s*([\s\S]*?)\s*```/gi) || [];
+  for (const block of fenced) {
+    const m = block.match(/```(?:json)?\s*([\s\S]*?)\s*```/i);
+    if (m && m[1]) {
+      candidates.push(asString(m[1]));
+    }
+  }
+  const keyIdx = trimmed.toLowerCase().indexOf('tool_calls');
+  if (keyIdx >= 0) {
+    const start = trimmed.slice(0, keyIdx).lastIndexOf('{');
+    if (start >= 0) {
+      const obj = extractJSONObjectFrom(trimmed, start);
+      if (obj.ok) {
+        candidates.push(asString(trimmed.slice(start, obj.end)));
+      }
+    }
+  }
+  const first = trimmed.indexOf('{');
+  const last = trimmed.lastIndexOf('}');
+  if (first >= 0 && last > first) {
+    candidates.push(asString(trimmed.slice(first, last + 1)));
+  }
+  return [...new Set(candidates.filter(Boolean))];
+}
+
+function parseToolCallsPayload(payload) {
+  let decoded;
+  try {
+    decoded = JSON.parse(payload);
+  } catch (_err) {
+    return [];
+  }
+  if (Array.isArray(decoded)) {
+    return parseToolCallList(decoded);
+  }
+  if (!decoded || typeof decoded !== 'object') {
+    return [];
+  }
+  if (decoded.tool_calls) {
+    return parseToolCallList(decoded.tool_calls);
+  }
+  const one = parseToolCallItem(decoded);
+  return one ? [one] : [];
+}
+
+function parseToolCallList(v) {
+  if (!Array.isArray(v)) {
+    return [];
+  }
+  const out = [];
+  for (const item of v) {
+    if (!item || typeof item !== 'object') {
+      continue;
+    }
+    const one = parseToolCallItem(item);
+    if (one) {
+      out.push(one);
+    }
+  }
+  return out;
+}
+
+function parseToolCallItem(m) {
+  let name = asString(m.name);
+  let inputRaw = m.input;
+  let hasInput = Object.prototype.hasOwnProperty.call(m, 'input');
+  const fn = m.function && typeof m.function === 'object' ? m.function : null;
+  if (fn) {
+    if (!name) {
+      name = asString(fn.name);
+    }
+    if (!hasInput && Object.prototype.hasOwnProperty.call(fn, 'arguments')) {
+      inputRaw = fn.arguments;
+      hasInput = true;
+    }
+  }
+  if (!hasInput) {
+    for (const k of ['arguments', 'args', 'parameters', 'params']) {
+      if (Object.prototype.hasOwnProperty.call(m, k)) {
+        inputRaw = m[k];
+        hasInput = true;
+        break;
+      }
+    }
+  }
+  if (!name) {
+    return null;
+  }
+  return {
+    name,
+    input: parseToolCallInput(inputRaw),
+  };
+}
+
+function parseToolCallInput(v) {
+  if (v == null) {
+    return {};
+  }
+  if (typeof v === 'string') {
+    const raw = asString(v);
+    if (!raw) {
+      return {};
+    }
+    try {
+      const parsed = JSON.parse(raw);
+      if (parsed && typeof parsed === 'object' && !Array.isArray(parsed)) {
+        return parsed;
+      }
+    } catch (_err) {
+      return { _raw: raw };
+    }
+    return {};
+  }
+  if (typeof v === 'object' && !Array.isArray(v)) {
+    return v;
+  }
+  try {
+    const parsed = JSON.parse(JSON.stringify(v));
+    if (parsed && typeof parsed === 'object' && !Array.isArray(parsed)) {
+      return parsed;
+    }
+  } catch (_err) {
+    return {};
+  }
+  return {};
+}
+
+function formatOpenAIStreamToolCalls(calls) {
+  if (!Array.isArray(calls) || calls.length === 0) {
+    return [];
+  }
+  return calls.map((c, idx) => ({
+    index: idx,
+    id: `call_${newCallID()}`,
+    type: 'function',
+    function: {
+      name: c.name,
+      arguments: JSON.stringify(c.input || {}),
+    },
+  }));
+}
+
+function newCallID() {
+  if (typeof crypto.randomUUID === 'function') {
+    return crypto.randomUUID().replace(/-/g, '');
+  }
+  return `${Date.now()}${Math.floor(Math.random() * 1e9)}`;
+}
diff --git a/internal/adapter/openai/handler.go b/internal/adapter/openai/handler.go
index 99793b7..78e9164 100644
--- a/internal/adapter/openai/handler.go
+++ b/internal/adapter/openai/handler.go
@@ -39,6 +39,17 @@ type streamLease struct {
 	ExpiresAt time.Time
 }
 
+type toolStreamSieveState struct {
+	pending   strings.Builder
+	capture   strings.Builder
+	capturing bool
+}
+
+type toolStreamEvent struct {
+	Content   string
+	ToolCalls []util.ParsedToolCall
+}
+
 func RegisterRoutes(r chi.Router, h *Handler) {
 	r.Get("/v1/models", h.ListModels)
 	r.Post("/v1/chat/completions", h.ChatCompletions)
@@ -376,6 +387,8 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 	created := time.Now().Unix()
 	firstChunkSent := false
 	bufferToolContent := len(toolNames) > 0
+	var toolSieve toolStreamSieveState
+	toolCallsEmitted := false
 	currentType := "text"
 	if thinkingEnabled {
 		currentType = "thinking"
@@ -408,7 +421,7 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 		finalThinking := thinking.String()
 		finalText := text.String()
 		detected := util.ParseToolCalls(finalText, toolNames)
-		if len(detected) > 0 {
+		if len(detected) > 0 && !toolCallsEmitted {
 			finishReason = "tool_calls"
 			delta := map[string]any{
 				"tool_calls": util.FormatOpenAIStreamToolCalls(detected),
@@ -424,21 +437,29 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 				"model":   model,
 				"choices": []map[string]any{{"delta": delta, "index": 0}},
 			})
-		} else if bufferToolContent && strings.TrimSpace(finalText) != "" {
-			delta := map[string]any{
-				"content": finalText,
+		} else if bufferToolContent {
+			for _, evt := range flushToolSieve(&toolSieve, toolNames) {
+				if evt.Content == "" {
+					continue
+				}
+				delta := map[string]any{
+					"content": evt.Content,
+				}
+				if !firstChunkSent {
+					delta["role"] = "assistant"
+					firstChunkSent = true
+				}
+				sendChunk(map[string]any{
+					"id":      completionID,
+					"object":  "chat.completion.chunk",
+					"created": created,
+					"model":   model,
+					"choices": []map[string]any{{"delta": delta, "index": 0}},
+				})
 			}
-			if !firstChunkSent {
-				delta["role"] = "assistant"
-				firstChunkSent = true
-			}
-			sendChunk(map[string]any{
-				"id":      completionID,
-				"object":  "chat.completion.chunk",
-				"created": created,
-				"model":   model,
-				"choices": []map[string]any{{"delta": delta, "index": 0}},
-			})
+		}
+		if len(detected) > 0 || toolCallsEmitted {
+			finishReason = "tool_calls"
 		}
 		promptTokens := util.EstimateTokens(finalPrompt)
 		reasoningTokens := util.EstimateTokens(finalThinking)
@@ -532,6 +553,41 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 					text.WriteString(p.Text)
 					if !bufferToolContent {
 						delta["content"] = p.Text
+					} else {
+						events := processToolSieveChunk(&toolSieve, p.Text, toolNames)
+						if len(events) == 0 {
+							// Keep thinking delta only frame.
+						}
+						for _, evt := range events {
+							if len(evt.ToolCalls) > 0 {
+								toolCallsEmitted = true
+								tcDelta := map[string]any{
+									"tool_calls": util.FormatOpenAIStreamToolCalls(evt.ToolCalls),
+								}
+								if !firstChunkSent {
+									tcDelta["role"] = "assistant"
+									firstChunkSent = true
+								}
+								newChoices = append(newChoices, map[string]any{
+									"delta": tcDelta,
+									"index": 0,
+								})
+								continue
+							}
+							if evt.Content != "" {
+								contentDelta := map[string]any{
+									"content": evt.Content,
+								}
+								if !firstChunkSent {
+									contentDelta["role"] = "assistant"
+									firstChunkSent = true
+								}
+								newChoices = append(newChoices, map[string]any{
+									"delta": contentDelta,
+									"index": 0,
+								})
+							}
+						}
 					}
 				}
 				if len(delta) > 0 {
@@ -669,6 +725,224 @@ func vercelInternalSecret() string {
 	return "admin"
 }
 
+func shouldEmitBufferedToolProbeContent(buffered string) bool {
+	trimmed := strings.TrimSpace(buffered)
+	if trimmed == "" {
+		return false
+	}
+	normalized := normalizeToolProbePrefix(trimmed)
+	if normalized == "" {
+		return false
+	}
+	first := normalized[0]
+	switch first {
+	case '{', '[', '`':
+		lower := strings.ToLower(normalized)
+		if strings.Contains(lower, "tool_calls") {
+			return false
+		}
+		// Keep a short hold window for JSON-ish starts to avoid leaking tool JSON.
+		if len([]rune(normalized)) < 20 {
+			return false
+		}
+		return true
+	default:
+		// Natural language starts can be streamed immediately.
+		return true
+	}
+}
+
+func normalizeToolProbePrefix(s string) string {
+	t := strings.TrimSpace(s)
+	if strings.HasPrefix(t, "```") {
+		t = strings.TrimPrefix(t, "```")
+		t = strings.TrimSpace(t)
+		t = strings.TrimPrefix(strings.ToLower(t), "json")
+		t = strings.TrimSpace(t)
+	}
+	return t
+}
+
+func processToolSieveChunk(state *toolStreamSieveState, chunk string, toolNames []string) []toolStreamEvent {
+	if state == nil || chunk == "" {
+		return nil
+	}
+	state.pending.WriteString(chunk)
+	events := make([]toolStreamEvent, 0, 2)
+
+	for {
+		if state.capturing {
+			if state.pending.Len() > 0 {
+				state.capture.WriteString(state.pending.String())
+				state.pending.Reset()
+			}
+			prefix, calls, suffix, ready := consumeToolCapture(state.capture.String(), toolNames)
+			if !ready {
+				break
+			}
+			state.capture.Reset()
+			state.capturing = false
+			if prefix != "" {
+				events = append(events, toolStreamEvent{Content: prefix})
+			}
+			if len(calls) > 0 {
+				events = append(events, toolStreamEvent{ToolCalls: calls})
+			}
+			if suffix != "" {
+				state.pending.WriteString(suffix)
+			}
+			continue
+		}
+
+		pending := state.pending.String()
+		if pending == "" {
+			break
+		}
+		start := findToolSegmentStart(pending)
+		if start >= 0 {
+			prefix := pending[:start]
+			if prefix != "" {
+				events = append(events, toolStreamEvent{Content: prefix})
+			}
+			state.pending.Reset()
+			state.capture.WriteString(pending[start:])
+			state.capturing = true
+			continue
+		}
+
+		safe, hold := splitSafeContent(pending, 64)
+		if safe == "" {
+			break
+		}
+		state.pending.Reset()
+		state.pending.WriteString(hold)
+		events = append(events, toolStreamEvent{Content: safe})
+	}
+
+	return events
+}
+
+func flushToolSieve(state *toolStreamSieveState, toolNames []string) []toolStreamEvent {
+	if state == nil {
+		return nil
+	}
+	events := processToolSieveChunk(state, "", toolNames)
+	if state.capturing {
+		raw := state.capture.String()
+		state.capture.Reset()
+		state.capturing = false
+		if raw != "" {
+			events = append(events, toolStreamEvent{Content: raw})
+		}
+	}
+	if state.pending.Len() > 0 {
+		events = append(events, toolStreamEvent{Content: state.pending.String()})
+		state.pending.Reset()
+	}
+	return events
+}
+
+func splitSafeContent(s string, holdRunes int) (safe, hold string) {
+	if s == "" || holdRunes <= 0 {
+		return s, ""
+	}
+	runes := []rune(s)
+	if len(runes) <= holdRunes {
+		return "", s
+	}
+	return string(runes[:len(runes)-holdRunes]), string(runes[len(runes)-holdRunes:])
+}
+
+func findToolSegmentStart(s string) int {
+	if s == "" {
+		return -1
+	}
+	lower := strings.ToLower(s)
+	keyIdx := strings.Index(lower, "tool_calls")
+	if keyIdx < 0 {
+		return -1
+	}
+	if start := strings.LastIndex(s[:keyIdx], "{"); start >= 0 {
+		return start
+	}
+	return keyIdx
+}
+
+func consumeToolCapture(captured string, toolNames []string) (prefix string, calls []util.ParsedToolCall, suffix string, ready bool) {
+	if captured == "" {
+		return "", nil, "", false
+	}
+	lower := strings.ToLower(captured)
+	keyIdx := strings.Index(lower, "tool_calls")
+	if keyIdx < 0 {
+		if len([]rune(captured)) >= 256 {
+			return captured, nil, "", true
+		}
+		return "", nil, "", false
+	}
+	start := strings.LastIndex(captured[:keyIdx], "{")
+	if start < 0 {
+		if len([]rune(captured)) >= 512 {
+			return captured, nil, "", true
+		}
+		return "", nil, "", false
+	}
+	obj, end, ok := extractJSONObjectFrom(captured, start)
+	if !ok {
+		if len([]rune(captured)) >= 4096 {
+			return captured, nil, "", true
+		}
+		return "", nil, "", false
+	}
+	parsed := util.ParseToolCalls(obj, toolNames)
+	if len(parsed) == 0 {
+		return captured[:end], nil, captured[end:], true
+	}
+	return captured[:start], parsed, captured[end:], true
+}
+
+func extractJSONObjectFrom(text string, start int) (string, int, bool) {
+	if start < 0 || start >= len(text) || text[start] != '{' {
+		return "", 0, false
+	}
+	depth := 0
+	quote := byte(0)
+	escaped := false
+	for i := start; i < len(text); i++ {
+		ch := text[i]
+		if quote != 0 {
+			if escaped {
+				escaped = false
+				continue
+			}
+			if ch == '\\' {
+				escaped = true
+				continue
+			}
+			if ch == quote {
+				quote = 0
+			}
+			continue
+		}
+		if ch == '"' || ch == '\'' {
+			quote = ch
+			continue
+		}
+		if ch == '{' {
+			depth++
+			continue
+		}
+		if ch == '}' {
+			depth--
+			if depth == 0 {
+				end := i + 1
+				return text[start:end], end, true
+			}
+		}
+	}
+	return "", 0, false
+}
+
 func (h *Handler) holdStreamLease(a *auth.RequestAuth) string {
 	if a == nil {
 		return ""
diff --git a/internal/adapter/openai/handler_toolcall_test.go b/internal/adapter/openai/handler_toolcall_test.go
index 6bc8d30..e3cfc7d 100644
--- a/internal/adapter/openai/handler_toolcall_test.go
+++ b/internal/adapter/openai/handler_toolcall_test.go
@@ -335,3 +335,84 @@ func TestHandleStreamUnknownToolStillIntercepted(t *testing.T) {
 		t.Fatalf("raw tool_calls JSON leaked in content delta: %s", rec.Body.String())
 	}
 }
+
+func TestHandleStreamToolsPlainTextStreamsBeforeFinish(t *testing.T) {
+	h := &Handler{}
+	resp := makeSSEHTTPResponse(
+		`data: {"p":"response/content","v":"你好，"}`,
+		`data: {"p":"response/content","v":"这是普通文本回复。"}`,
+		`data: [DONE]`,
+	)
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	h.handleStream(rec, req, resp, "cid6", "deepseek-chat", "prompt", false, false, []string{"search"})
+
+	frames, done := parseSSEDataFrames(t, rec.Body.String())
+	if !done {
+		t.Fatalf("expected [DONE], body=%s", rec.Body.String())
+	}
+	if streamHasToolCallsDelta(frames) {
+		t.Fatalf("did not expect tool_calls delta for plain text: %s", rec.Body.String())
+	}
+	content := strings.Builder{}
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			if c, ok := delta["content"].(string); ok {
+				content.WriteString(c)
+			}
+		}
+	}
+	if got := content.String(); got == "" {
+		t.Fatalf("expected streamed content in tool mode plain text, body=%s", rec.Body.String())
+	}
+	if streamFinishReason(frames) != "stop" {
+		t.Fatalf("expected finish_reason=stop, body=%s", rec.Body.String())
+	}
+}
+
+func TestHandleStreamToolCallMixedWithPlainTextSegments(t *testing.T) {
+	h := &Handler{}
+	resp := makeSSEHTTPResponse(
+		`data: {"p":"response/content","v":"前置正文A。"}`,
+		`data: {"p":"response/content","v":"{\"tool_calls\":[{\"name\":\"search\",\"input\":{\"q\":\"go\"}}]}"}`,
+		`data: {"p":"response/content","v":"后置正文B。"}`,
+		`data: [DONE]`,
+	)
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	h.handleStream(rec, req, resp, "cid7", "deepseek-chat", "prompt", false, false, []string{"search"})
+
+	frames, done := parseSSEDataFrames(t, rec.Body.String())
+	if !done {
+		t.Fatalf("expected [DONE], body=%s", rec.Body.String())
+	}
+	if !streamHasToolCallsDelta(frames) {
+		t.Fatalf("expected tool_calls delta in mixed stream, body=%s", rec.Body.String())
+	}
+	if streamHasRawToolJSONContent(frames) {
+		t.Fatalf("raw tool_calls JSON leaked in mixed stream: %s", rec.Body.String())
+	}
+	content := strings.Builder{}
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			if c, ok := delta["content"].(string); ok {
+				content.WriteString(c)
+			}
+		}
+	}
+	got := content.String()
+	if !strings.Contains(got, "前置正文A。") || !strings.Contains(got, "后置正文B。") {
+		t.Fatalf("expected pre/post plain text to pass sieve, got=%q", got)
+	}
+	if streamFinishReason(frames) != "tool_calls" {
+		t.Fatalf("expected finish_reason=tool_calls, body=%s", rec.Body.String())
+	}
+}
diff --git a/vercel.json b/vercel.json
index 0645290..2e68a94 100644
--- a/vercel.json
+++ b/vercel.json
@@ -4,7 +4,11 @@
   "outputDirectory": "static",
   "functions": {
     "api/chat-stream.js": {
-      "includeFiles": "**/sha3_wasm_bg.7b9ca65ddd.wasm"
+      "includeFiles": "**/sha3_wasm_bg.7b9ca65ddd.wasm",
+      "maxDuration": 300
+    },
+    "api/index.go": {
+      "maxDuration": 300
     }
   },
   "rewrites": [
diff --git a/webui/src/components/ApiTester.jsx b/webui/src/components/ApiTester.jsx
index c2c228a..7d49982 100644
--- a/webui/src/components/ApiTester.jsx
+++ b/webui/src/components/ApiTester.jsx
@@ -115,7 +115,8 @@ export default function ApiTester({ config, onMessage, authFetch }) {
                 headers['X-Ds2-Target-Account'] = selectedAccount
             }
 
-            const res = await fetch('/v1/chat/completions', {
+            const endpoint = streamingMode ? '/v1/chat/completions' : '/v1/chat/completions?__go=1'
+            const res = await fetch(endpoint, {
                 method: 'POST',
                 headers,
                 body: JSON.stringify({