diff --git a/static/src/app/methods/taskPolling/probe.ts b/static/src/app/methods/taskPolling/probe.ts
index 342a4c97..21cc52c0 100644
--- a/static/src/app/methods/taskPolling/probe.ts
+++ b/static/src/app/methods/taskPolling/probe.ts
@@ -73,7 +73,15 @@ export const probeMethods = {
     if (status.is_truly_active) {
       this._runningStateIdleStreak = 0;
       // 恢复方向（立即执行，宁多勿漏）：服务端活跃但本地缺轮询/缺标志位
-      if (status.is_main_running && status.main_task_id && !taskStore.hasActiveTask) {
+      // 幂等约束：本地已在轮询同一任务时不介入。服务端把 pending/cancel_requested
+      // 也算活跃，而 hasActiveTask 只认 'running'，旧判定（!hasActiveTask）会把
+      // 排队中/停止收尾中的活任务误判为「缺轮询」，每 2.5s 触发一次「清去重 +
+      // 偏移归零」的全量事件重放，导致进度块周期性整份重复追加（页面卡死根因）。
+      const alreadyTrackingMain =
+        !!status.main_task_id &&
+        taskStore.currentTaskId === status.main_task_id &&
+        taskStore.isPolling;
+      if (status.is_main_running && status.main_task_id && !alreadyTrackingMain) {
         debugNotifyLog('[DEBUG_NOTIFY][ui] reconcile:resume-main-task', {
           taskId: status.main_task_id,
           conversationId
@@ -87,6 +95,9 @@ export const probeMethods = {
           eventHandler: (event: any) => this.handleTaskEvent(event)
         });
         this.taskInProgress = true;
+      } else if (status.is_main_running && alreadyTrackingMain) {
+        // 已在跟踪：仅幂等对齐标志位，绝不触碰去重集合与事件偏移
+        this.taskInProgress = true;
       }
       if (status.has_running_sub_agents) {
         this.waitingForSubAgent = true;
diff --git a/static/src/app/methods/taskPolling/tool.ts b/static/src/app/methods/taskPolling/tool.ts
index a89de13d..ef568e75 100644
--- a/static/src/app/methods/taskPolling/tool.ts
+++ b/static/src/app/methods/taskPolling/tool.ts
@@ -43,6 +43,26 @@ export const toolMethods = {
       msg.generatingLabel = '';
     }
 
+    // 幂等兜底：同 id 的工具块已存在（重复/重放事件）时复用，不重复 push。
+    // 若块已进入 running（tool_start 已处理），不得把状态回退为 preparing。
+    let existingAction = null;
+    if (data.id && this.preparingTools.has(data.id)) {
+      existingAction = this.preparingTools.get(data.id);
+    } else if (data.id) {
+      existingAction = this.toolFindAction(data.id, data.preparing_id, data.execution_id);
+    }
+    if (existingAction) {
+      if (String(existingAction.tool?.status || '').toLowerCase() === 'preparing') {
+        existingAction.tool.message = data.message || existingAction.tool.message;
+        if (data.intent) {
+          existingAction.tool.intent_full = data.intent;
+          existingAction.tool.intent_rendered = data.intent;
+        }
+        this.$forceUpdate();
+      }
+      return;
+    }
+
     const action = {
       id: data.id,
       type: 'tool',
diff --git a/static/src/stores/chat.ts b/static/src/stores/chat.ts
index 81c770bc..9a9bedc0 100644
--- a/static/src/stores/chat.ts
+++ b/static/src/stores/chat.ts
@@ -232,6 +232,13 @@ export const useChatStore = defineStore('chat', {
     startThinkingAction() {
       const msg = this.ensureAssistantMessage();
       clearAwaitingFirstContent(msg);
+      // 幂等兜底：已有「流式中」的思考块时复用而非新建。正常流程
+      // thinking_start/thinking_end 成对出现，end 会把 streaming 置 false，
+      // 因此命中流式块只可能来自重复/重放事件（去重集合被清后的最后防线）。
+      const existingThinking = this.getActiveThinkingAction(msg);
+      if (existingThinking && existingThinking.streaming === true) {
+        return { action: existingThinking, blockId: existingThinking.blockId || existingThinking.id };
+      }
       msg.streamingThinking = '';
       msg.currentStreamingType = 'thinking';
       const actionId = randomId('thinking');
@@ -279,6 +286,13 @@ export const useChatStore = defineStore('chat', {
         return null;
       }
       clearAwaitingFirstContent(msg);
+      // 幂等兜底：末尾已有「流式中」的文本块时复用而非新建。正常流程
+      // text_start/text_end 成对出现，end 会把 streaming 置 false，
+      // 因此命中流式块只可能来自重复/重放事件（去重集合被清后的最后防线）。
+      const lastAction = msg.actions[msg.actions.length - 1];
+      if (lastAction && lastAction.type === 'text' && lastAction.streaming === true) {
+        return lastAction;
+      }
       msg.streamingText = '';
       msg.currentStreamingType = 'text';
       (msg as any).__splitByShowHtml = false;
diff --git a/static/src/stores/task.ts b/static/src/stores/task.ts
index e33bd70f..c7d599b4 100644
--- a/static/src/stores/task.ts
+++ b/static/src/stores/task.ts
@@ -499,13 +499,24 @@ export const useTaskStore = defineStore('task', {
         currentTaskId: this.currentTaskId,
         resetOffset: options?.resetOffset !== false
       });
+      const isSameTask = !!this.currentTaskId && this.currentTaskId === taskId;
+      const wasPolling = this.isPolling;
       if (this.currentTaskId && this.currentTaskId !== taskId) {
         this.stopPolling();
       }
       this.currentTaskId = taskId;
       this.taskStatus = options.status || 'running';
-      if (options.resetOffset !== false) {
+      // resetOffset 收编：仅允许「真正的冷启动恢复」（不同任务或轮询已停）归零偏移。
+      // 同任务且轮询在跑时归零，下一次轮询会从 0 全量重拉事件；若去重集合恰好
+      // 被清（对账/恢复路径），进度块会整份重复追加。
+      if (options.resetOffset !== false && !(isSameTask && wasPolling)) {
         this.lastEventIndex = 0;
+      } else if (options.resetOffset !== false) {
+        goalModeDebugLog('taskStore.resumeTask_resetOffset_skipped', {
+          taskId,
+          reason: 'same-task-polling-active',
+          lastEventIndex: this.lastEventIndex
+        });
       }
       this.pollingError = null;
       this.runtimeQueueSnapshotKey = '';