fix(webui): SSE消息同步不及时 + 后端缓冲加固

handler.go:
- writeCh 512→2048，新增 sendSSE() 函数（100ms短超时重试替代立即丢弃）
- After(id) 为空时发送 sync_required 事件通知前端补拉历史
- 批量 flush 阈值 64→128

dashboard.html:
- 新增 syncChatFromHistory()：增量同步，仅追加新消息DOM节点，不重建已有消息→无闪烁
- 监听 sync_required 事件触发增量补拉
- SSE onerror 立即 close 阻止双连接竞态，2s后手动重连（原5s）
- init 顺序：先 loadChatHistory 再 connectSSE（避免事件与历史加载竞态）
- 30s轮询兜底（补偿SSE断连窗口期丢失的跨渠道消息）

internal/plugins/webui/dashboard.html

@@ -4206,6 +4206,87 @@
         } catch (e) {}
       }
 
+      // syncChatFromHistory 增量同步：对比服务端历史，仅追加新消息 DOM 节点，
+      // 不重建已有消息 → 无闪烁。用于 SSE 断连恢复期间的轮询兜底。
+      function syncChatFromHistory() {
+        return api("/chat/history").then(function (data) {
+          if (!data || !data.messages || data.messages.length === 0) return;
+          var serverMsgs = data.messages;
+          var localMsgs = state.messages;
+          // 空历史 → 全量加载（首次同步）
+          if (localMsgs.length === 0) {
+            state.messages = serverMsgs;
+            rerenderChat(true);
+            return;
+          }
+          // 无新增消息 → 检查最后一条是否被改写
+          if (serverMsgs.length <= localMsgs.length) {
+            var lastLocal = localMsgs[localMsgs.length - 1];
+            var lastServer = serverMsgs[serverMsgs.length - 1];
+            var localContent = lastLocal.content || lastLocal.Content || "";
+            var serverContent = lastServer.content || lastServer.Content || "";
+            if (lastServer.role === "assistant" && localContent !== serverContent && serverContent) {
+              lastLocal.content = serverContent;
+              if (lastServer.ReasoningContent) lastLocal.reasoning_content = lastServer.ReasoningContent;
+              // 仅更新最后一条消息 DOM，不全量重建
+              var msgsEl = document.getElementById("chat-msgs");
+              if (msgsEl && msgsEl.lastElementChild) {
+                var el = msgsEl.lastElementChild;
+                var textEl = el.querySelector(".msg-bubble .text");
+                if (textEl) textEl.innerHTML = renderMd(serverContent);
+              }
+            }
+            return;
+          }
+          // 有新增消息：追加到 state.messages + DOM（仅追加节点，不触碰已有）
+          var newMsgs = serverMsgs.slice(localMsgs.length);
+          var msgsEl = document.getElementById("chat-msgs");
+          if (msgsEl) {
+            var aiAvatar = '<img src="/mascot.webp" alt="小宅">';
+            var userAvatar = '<svg viewBox="0 0 24 24" style="width:16px;height:16px" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"><circle cx="12" cy="8" r="4"/><path d="M4 20c0-4 4-6 8-6s8 2 8 6"/></svg>';
+            newMsgs.forEach(function (m) {
+              var role = m.role || m.Role || "user";
+              var c = m.content || m.Content || "";
+              if (role === "assistant") c = renderMd(c); else c = escHtml(c);
+              var isChan = !!(m.source && m.source !== "webui");
+              var bubble = c ? '<div class="msg-bubble"><div class="text">' + c + '</div></div>' : '<div class="msg-bubble"></div>';
+              if (role === "system") {
+                msgsEl.insertAdjacentHTML("beforeend", '<div class="msg msg-system"><div class="msg-bubble">' + c + '</div></div>');
+              } else if (isChan) {
+                msgsEl.insertAdjacentHTML("beforeend", '<div class="msg msg-channel"><div class="msg-avatar chan-avatar" style="background:#888">' + (m.source||"?")[0].toUpperCase() + '</div><div class="msg-content"><div class="msg-chan-name">' + escHtml(m.source) + '</div>' + bubble + '</div></div>');
+              } else {
+                msgsEl.insertAdjacentHTML("beforeend", '<div class="msg msg-' + role + '"><div class="msg-avatar">' + (role === "user" ? userAvatar : aiAvatar) + '</div><div class="msg-content">' + bubble + '</div></div>');
+              }
+            });
+            // 删除流式占位符（同步完成，下一次 SSE 会重建）
+            var streamingPh = msgsEl.querySelector(".msg-streaming-ph");
+            if (streamingPh) streamingPh.remove();
+          }
+          // 追加新消息对象到 state.messages
+          Array.prototype.push.apply(state.messages, newMsgs);
+          // 同步聊天占位符（如果有新消息但最后一条非 assistant → 显示流式占位）
+          syncStreamingPlaceholder();
+        }).catch(function () {});
+      }
+      // syncStreamingPlaceholder：同步聊天占位符的可见性
+      function syncStreamingPlaceholder() {
+        var msgsEl = document.getElementById("chat-msgs");
+        if (!msgsEl) return;
+        var existing = msgsEl.querySelector(".msg-streaming-ph");
+        var lastMsg = state.messages.length ? state.messages[state.messages.length - 1] : null;
+        var showPh = state.chatLoading && (!lastMsg || lastMsg.role !== "assistant" || lastMsg._final);
+        if (showPh && !existing) {
+          var aiAvatar = '<img src="/mascot.webp" alt="小宅">';
+          var pillHtml = "";
+          (state.pendingTools || []).forEach(function (nm) {
+            pillHtml += '<span class="thinking-tool"><svg viewBox="0 0 24 24" width="11" height="11" fill="none" stroke="currentColor" stroke-width="2"><path d="M14.7 6.3a4 4 0 0 0-5.4 5.4L3 18l3 3 6.3-6.3a4 4 0 0 0 5.4-5.4l-2.9 2.9-2.5-.6-.6-2.5z"/></svg>' + escHtml(nm) + '</span>';
+          });
+          msgsEl.insertAdjacentHTML("beforeend", '<div class="msg msg-assistant msg-streaming-ph"><div class="msg-avatar">' + aiAvatar + '</div><div class="msg-content"><div class="msg-bubble"><span class="live-spinner"></span>' + (pillHtml ? '<span class="thinking-tools">' + pillHtml + '</span>' : '') + '</div></div></div>');
+        } else if (!showPh && existing) {
+          existing.remove();
+        }
+      }
+
       async function loadTerminals() {
         try {
           var data = await api("/terminals");
@@ -4649,8 +4730,19 @@
         };
         es.onerror = function (e) {
           console.error("[SSE] error", e);
-          setTimeout(connectSSE, 5000);
+          // 1) 立即 close 阻止浏览器原生自动重连与手动 setTimeout(connectSSE) 双连接竞态
+          try { state.eventSource && state.eventSource.close(); state.eventSource = null; } catch(ex){}
+          // 2) 连接错误期间可能丢失事件，增量补拉历史（无闪烁）
+          syncChatFromHistory().catch(function(){});
+          // 3) 2s 后手动重连（比原 5s 更快恢复）
+          setTimeout(connectSSE, 2000);
         };
+        // sync_required：Server 因 Last-Event-ID 不在 ring（delta ID / 已到 tip）无法重放，
+        // 通知前端增量补拉历史——避免前端空等后续聚合事件导致「消息同步不及时」。
+        es.addEventListener("sync_required", function(e) {
+          console.log("[SSE] sync_required received, incremental sync");
+          syncChatFromHistory().catch(function(){});
+        });
         // Periodically refresh sidebar data
         if (state._sidebarRefresh) clearInterval(state._sidebarRefresh);
         state._sidebarRefresh = setInterval(async function () {
@@ -6278,13 +6370,20 @@
       }
 
       renderConfigDisabled();
-      connectSSE();
+      // 先加载历史再连 SSE：避免 SSE 事件先到与历史加载顺序不确定导致消息重复/丢失
       (async function () {
         await loadChatHistory();
         renderAll();
+        connectSSE();
         startUptimeTicker();
       })();
       setInterval(renderAll, 15000);
+      // 消息同步轮询兜底：每30秒增量同步 chatHistory，补偿 SSE 断连窗口期
+      // 丢失的事件（尤其是非 WebUI 触发的跨渠道消息，如 CLI/QQ/设备桥输出）。
+      // syncChatFromHistory 仅追加新消息 DOM 节点，不重建已有消息，无闪烁。
+      setInterval(function () {
+        syncChatFromHistory().catch(function(){});
+      }, 30000);
     </script>
   </body>
 </html>

internal/plugins/webui/handler.go

@@ -1669,6 +1669,25 @@ func (h *Handler) handleChat(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, result)
 }
 
+// sendSSE 向 writeCh 发送一条 SSE 事件；队列满时等 100ms 再试，
+// 比立即 drop 更友好，避免密集 tool_call/delta 期间前端丢帧。
+func sendSSE(writeCh chan string, id, eventType, data string) {
+	line := fmt.Sprintf("id: %s\nevent: %s\ndata: %s\n", id, eventType, data)
+	select {
+	case writeCh <- line:
+		return
+	default:
+	}
+	// 队列满：等 100ms 让 writer flush，再试一次
+	timer := time.NewTimer(100 * time.Millisecond)
+	defer timer.Stop()
+	select {
+	case writeCh <- line:
+	case <-timer.C:
+		log.Printf("[SSE] DROPPED %s id=%s (writeCh full 100ms, len=%d)", eventType, id, len(writeCh))
+	}
+}
+
 func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 	if r.Method != http.MethodGet {
 		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
@@ -1700,10 +1719,10 @@ func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 	// writeCh 不 close：Subscribe 回调闭包持有它，handler 退出后回调仍可能被
 	// 总线异步触发，close 后再发送会 panic（send on closed channel，生产日志中
 	// 单日数千次）。writer goroutine 通过 done 退出；发送侧 select on done 防泄漏。
-	// 缓冲加大到 512 且 writer 做批量合并：reasoning/content 增量是高频小包，
+	// 缓冲 2048：reasoning/content 增量是高频小包（LLM token 级），
-	// 每条单独 flush 会因 socket 写慢而填满小缓冲导致 delta 被丢弃（表现为
+	// 512 时连续 tool_call + reasoning + delta 密集期会溢出导致前端丢帧。
-	// 前端只能等最终的 agent_output 整段，体感延迟）。
+	// 写入侧用短超时(50ms)兜底，比立即丢弃更友好。
-	writeCh := make(chan string, 512)
+	writeCh := make(chan string, 2048)
 	writerDone := make(chan struct{})
 	go func() {
 		defer func() {
@@ -1731,7 +1750,8 @@ func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 			select {
 			case line := <-writeCh:
 				pending = append(pending, line)
-				if len(pending) >= 64 {
+				// 大批量一次性 flush：阈值从 64 提高，利用批量减少 syscall 开销
+				if len(pending) >= 128 {
 					flushPending()
 				}
 			case <-flushTicker.C:
@@ -1754,6 +1774,10 @@ func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 			replayed := h.sseEvents.After(lastEventID)
 			if len(replayed) == 0 {
 				log.Printf("[SSE] replay: nothing after id %s (id not in ring or already at tip)", lastEventID)
+				// ID 不在 ring：说明最后一帧是 delta（delta 不进 ring）或已到最新。
+				// 显式通知前端补拉历史，避免其空等后续聚合事件（表现为消息同步不及时）。
+				fmt.Fprintf(w, "event: sync_required\ndata: {}\n\n")
+				flusher.Flush()
 			} else {
 				log.Printf("[SSE] replay: sending %d events after id %s", len(replayed), lastEventID)
 				for _, rec := range replayed {
@@ -1776,11 +1800,7 @@ func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 			data, _ := json.Marshal(evt)
 			seq++
 			id := fmt.Sprintf("%d-%d", evt.Timestamp, seq)
-			select {
+			sendSSE(writeCh, id, string(evt.Type), string(data))
-			case writeCh <- fmt.Sprintf("id: %s\nevent: %s\ndata: %s\n", id, evt.Type, string(data)):
-			default:
-				log.Printf("[SSE] DROPPED %s (writeCh full, len=%d)", evt.Type, len(writeCh))
-			}
 		})
 		unsubs = append(unsubs, unsub)
 	}
@@ -1801,14 +1821,10 @@ func (h *Handler) handleChatEvents(w http.ResponseWriter, r *http.Request) {
 			if h.sseEvents != nil {
 				h.sseEvents.Append(id, string(evt.Type), data)
 			}
-			select {
+			sendSSE(writeCh, id, string(evt.Type), string(data))
-			case writeCh <- fmt.Sprintf("id: %s\nevent: %s\ndata: %s\n", id, evt.Type, string(data)):
+			if evt.Type == sdk.EventToolCall {
-				if evt.Type == sdk.EventToolCall {
+				toolName, _ := evt.Payload["tool"].(string)
-					toolName, _ := evt.Payload["tool"].(string)
+				log.Printf("[SSE] wrote tool_call to writeCh: tool=%s", toolName)
-					log.Printf("[SSE] wrote tool_call to writeCh: tool=%s", toolName)
-				}
-			default:
-				log.Printf("[SSE] DROPPED event %s (writeCh full, len=%d)", evt.Type, len(writeCh))
 			}
 		})
 		unsubs = append(unsubs, unsub)