diff --git a/ui/web/app.js b/ui/web/app.js
index 8548559..43cd878 100644
--- a/ui/web/app.js
+++ b/ui/web/app.js
@@ -31,23 +31,40 @@
     } catch (e) {}
 })();
 window.__APP_VER = '20260721-v7';
+// 流式逐 token 诊断默认关闭。逐 token 读取 DOM 高度/文本并写 console 会
+// 触发强制布局和跨进程日志传输，长时间运行会明显拖慢渲染器；需要排查时
+// 由 Python 显式调用 setStreamDiagnostics(true) 打开。
+window.__STREAM_DIAG = false;
+window.setStreamDiagnostics = function(enabled) {
+    window.__STREAM_DIAG = !!enabled;
+    if (window.__STREAM_DIAG && window.__startStreamHeartbeat) {
+        window.__startStreamHeartbeat();
+    }
+};
 console.log('[JS] ===== app.js 加载 ver=20260721-v7 =====');
 // 公式渲染依赖本地 KaTeX（离线）；此处确认资源加载结果，缺失时打印告警便于定位
 console.log('[JS] KaTeX ' + (typeof katex !== 'undefined' ? katex.version + ' 就绪' : '缺失（公式将退化为纯文本）'));
 // 渲染器主线程心跳：dt 异常大 = 渲染器被阻塞（截图/重绘/GPU 等）
 (function() {
     var _hbLast = Date.now();
-    setInterval(function() {
+    var _started = false;
+    function tick() {
         var _now = Date.now();
         var _dt = _now - _hbLast;
         _hbLast = _now;
         if (_dt >= 1500) {
             console.log('[JS] 心跳 dt=' + _dt + 'ms （渲染器主线程曾卡顿）');
         }
-    }, 1000);
+    }
+    window.__startStreamHeartbeat = function() {
+        if (_started) return;
+        _started = true;
+        setInterval(tick, 1000);
+    };
 })();
 window.__diag = { events: [], cap: 300, tokenN: 0, thinkN: 0 };
 function diagEvent(name, extra) {
+    if (!window.__STREAM_DIAG) return;
     try {
         var d = window.__diag;
         d.events.push({ t: Date.now() % 1000000, e: name, x: extra });
@@ -749,7 +766,8 @@ function createMessage(msgId, role, initialText, senderName, branchInfo) {
         if (role === 'user') {
             replyDiv.innerText = initialText;
         } else {
-            // 🆕 助手纯文本消息（无时间线历史路径）也包进 md-segment → 与时间线路径同样有浅灰气泡背景
+            // 🆕 助手纯文本消息（无时间线历史路径）也包进 md-segment，
+            // 与时间线路径保持相同的透明正文布局
             var _tHtml = typeof marked !== 'undefined' ? safeHtml(marked.parse(initialText)) : safeHtml(initialText);
             replyDiv.innerHTML = '<div class="md-segment markdown-body">' + _tHtml + '</div>';
         }
@@ -1208,7 +1226,8 @@ function syncRenderThrottled(msgId, minGapMs) {
 // Qt 看门狗入口：强制渲染（幂等，尾部无变化时开销极小）
 function forceRenderNow(msgId) {
     var _frNow = Date.now();
-    if (!window.__frLast || _frNow - window.__frLast > 1000) {
+    if (window.__STREAM_DIAG &&
+        (!window.__frLast || _frNow - window.__frLast > 1000)) {
         window.__frLast = _frNow;
         console.log('[JS] forceRenderNow id=' + msgId + ' (看门狗)');
     }
@@ -1236,7 +1255,7 @@ function _fullRenderSegment(el, c, isThink) {
 }
 function doStreamingRender(msgId) {
     window.__renderN = (window.__renderN || 0) + 1;
-    if (window.__renderN % 10 === 1) {
+    if (window.__STREAM_DIAG && window.__renderN % 10 === 1) {
         console.log('[JS] render#' + window.__renderN + ' 开始 id=' + msgId);
     }
     var buf = messageBuffer[msgId];
@@ -1288,9 +1307,11 @@ function appendReasoning(msgId, token) {
     buf.reasoning += token;
     var wrapper = document.getElementById(msgId);
     if (!wrapper) { diagEvent('appendReasoning', 'NO_WRAPPER:' + msgId); return; }
-    window.__diag.thinkN++;
-    if (window.__diag.thinkN === 1 || window.__diag.thinkN % 25 === 0) {
-        diagEvent('appendReasoning', 'n=' + window.__diag.thinkN);
+    if (window.__STREAM_DIAG) {
+        window.__diag.thinkN++;
+        if (window.__diag.thinkN === 1 || window.__diag.thinkN % 25 === 0) {
+            diagEvent('appendReasoning', 'n=' + window.__diag.thinkN);
+        }
     }
     wrapper.classList.add('streaming');
     var tl = ensureTimeline(wrapper, buf);
@@ -1308,7 +1329,11 @@ function appendReasoning(msgId, token) {
         buf.thinkSegs.push(tc);
     }
     tc.__buf = (tc.__buf || '') + token;
-    console.log('[JS] think#' + window.__diag.thinkN + ' 段buf=' + tc.__buf.length + 'c dom=' + (tc.textContent || '').length + 'c h=' + tc.offsetHeight);
+    if (window.__STREAM_DIAG) {
+        console.log('[JS] think#' + window.__diag.thinkN +
+            ' 段buf=' + tc.__buf.length + 'c dom=' +
+            (tc.textContent || '').length + 'c h=' + tc.offsetHeight);
+    }
     syncRenderThrottled(msgId);   // ★ 同步通道
     scheduleStreamingRender(msgId);
 }
@@ -1319,9 +1344,11 @@ function appendToken(msgId, token) {
     buf.content += token;
     var wrapper = document.getElementById(msgId);
     if (!wrapper) { diagEvent('appendToken', 'NO_WRAPPER:' + msgId); return; }
-    window.__diag.tokenN++;
-    if (window.__diag.tokenN === 1 || window.__diag.tokenN % 25 === 0) {
-        diagEvent('appendToken', 'n=' + window.__diag.tokenN);
+    if (window.__STREAM_DIAG) {
+        window.__diag.tokenN++;
+        if (window.__diag.tokenN === 1 || window.__diag.tokenN % 25 === 0) {
+            diagEvent('appendToken', 'n=' + window.__diag.tokenN);
+        }
     }
     wrapper.classList.add('streaming');
     var tl = ensureTimeline(wrapper, buf);
@@ -1345,9 +1372,14 @@ function appendToken(msgId, token) {
     } else {
         seg.__buf = (seg.__buf || '') + token;
     }
-    console.log('[JS] token#' + window.__diag.tokenN + ' 段buf=' + seg.__buf.length + 'c dom=' + (seg.textContent || '').length + 'c 段数=' + buf.textSegs.length + ' h=' + seg.offsetHeight);
-    if (window.__diag.tokenN === 1 || window.__diag.tokenN % 25 === 0) {
-        diagEvent('tokenDOM', { buf: seg.__buf.length, dom: (seg.textContent || '').length });
+    if (window.__STREAM_DIAG) {
+        console.log('[JS] token#' + window.__diag.tokenN +
+            ' 段buf=' + seg.__buf.length + 'c dom=' +
+            (seg.textContent || '').length + 'c 段数=' +
+            buf.textSegs.length + ' h=' + seg.offsetHeight);
+        if (window.__diag.tokenN === 1 || window.__diag.tokenN % 25 === 0) {
+            diagEvent('tokenDOM', { buf: seg.__buf.length, dom: (seg.textContent || '').length });
+        }
     }
     syncRenderThrottled(msgId);   // ★ 同步通道：token 到 → 内容必现
     scheduleStreamingRender(msgId);  // rAF 通道：更平滑（环境允许时）
@@ -1357,7 +1389,12 @@ function appendToken(msgId, token) {
 function finishMessage(msgId) {
     console.log('[JS] finishMessage id=' + msgId);
     var wrapper = document.getElementById(msgId);
-    if (!wrapper) { delete messageBuffer[msgId]; diagEvent('finish', 'NO_WRAPPER:' + msgId); return; }
+    if (!wrapper) {
+        delete messageBuffer[msgId];
+        delete __lastSyncRender[msgId];
+        diagEvent('finish', 'NO_WRAPPER:' + msgId);
+        return;
+    }
     diagEvent('finish', { id: msgId });
     var buf = messageBuffer[msgId];
     cancelStreamingRender(msgId);
@@ -1440,6 +1477,7 @@ function finishMessage(msgId) {
         if (buf.raf) { cancelAnimationFrame(buf.raf); buf.raf = 0; }
     }
     delete messageBuffer[msgId];
+    delete __lastSyncRender[msgId];
 
     // --- H. 刷新自定义滚动条 ---
     reportWebScroll();
@@ -1940,6 +1978,7 @@ function renderTimelineHistory(msgId, timelineJson) {
             // 删除 buffer → finishMessage 不再全量重渲（避免破坏时间线 DOM），
             // 但仍会执行代码高亮/滚动等收尾
             delete messageBuffer[msgId];
+            delete __lastSyncRender[msgId];
         }
     } catch (e) {
         console.error('[JS]: renderTimelineHistory 解析失败', e);
@@ -2063,6 +2102,23 @@ function hideLoadingOverlay() {
     setTimeout(function() { el.style.display = 'none'; }, 480);
 }
 
+// 消息从当前窗口移除时一并释放附件缓存。附件使用 msgId-att-N 作为键，
+// 只删除父消息键会让长文本和元数据跨会话持续留在内存中。
+function clearMessageStores(msgId) {
+    if (!msgId) return;
+    delete messageBuffer[msgId];
+    delete __lastSyncRender[msgId];
+    delete longTextStore[msgId];
+    delete finalContentStore[msgId];
+    delete attachmentMetaStore[msgId];
+    var prefix = msgId + '-att-';
+    [longTextStore, attachmentMetaStore].forEach(function(store) {
+        Object.keys(store).forEach(function(key) {
+            if (key.indexOf(prefix) === 0) delete store[key];
+        });
+    });
+}
+
 // ==================== 历史记录与视图控制 ====================
 function clearChat() {
     var bubbles = chatContainer.querySelectorAll('.message-wrapper, .system-note');
@@ -2073,6 +2129,7 @@ function clearChat() {
     longTextStore = {};
     finalContentStore = {};
     attachmentMetaStore = {};
+    __lastSyncRender = {};
 
     // 🆕 P1-01：清渲染窗口状态机（游标/缓存/未决请求/代次；配置模式与大小保留）
     if (typeof rwState !== 'undefined' && rwState && typeof RenderWindowState !== 'undefined') {
@@ -2093,9 +2150,7 @@ function deleteMessage(msgId) {
         wrapper.style.transform = "translateY(-10px)";
         setTimeout(function() { wrapper.remove(); }, 300);
     }
-    delete messageBuffer[msgId];
-    delete longTextStore[msgId];
-    delete finalContentStore[msgId];
+    clearMessageStores(msgId);
     setTimeout(reportWebScroll, 350);
 }
 
@@ -2267,10 +2322,7 @@ function rwCaptureAnchor() {
 function rwRemoveMessageDom(msgId) {
     var wrapper = document.getElementById(msgId);
     if (wrapper) wrapper.remove();
-    delete messageBuffer[msgId];
-    delete longTextStore[msgId];
-    delete finalContentStore[msgId];
-    delete attachmentMetaStore[msgId];
+    clearMessageStores(msgId);
 }
 
 /* 加载入口：固定在 chat-container 首/尾；无更多消息时隐藏。 */