frontend/src/pages/AssistantChatPage.tsx

@@ -142,6 +142,24 @@ export default function AssistantChatPage() {
     } catch { /* ignore */ }
     return false
   })
+  // Task-lane owner: the chatId these in-memory questions/actions/show
+  // values BELONG to, set every time we populate the lane. Render is gated
+  // on `taskLaneOwnerChatId === activeChatId` so any path that flips the
+  // active chat without clearing the lane state (in-place URL change,
+  // mid-flight pickup, etc.) cannot leak the previous chat's task data
+  // into the new view. The mount-time flash protection still lives in
+  // `skipTaskLaneRestore`; this guard handles every other transition.
+  const [taskLaneOwnerChatId, setTaskLaneOwnerChatId] = useState<string | null>(() => {
+    if (skipTaskLaneRestore) return null
+    try {
+      const saved = sessionStorage.getItem('rf-tasklane-meta')
+      if (saved) {
+        const d = JSON.parse(saved)
+        if (typeof d.chatId === 'string' && d.chatId === activeChatId) return d.chatId
+      }
+    } catch { /* ignore */ }
+    return null
+  })
   const [sidebarCollapsed, setSidebarCollapsed] = useState(() =>
     localStorage.getItem('rf-chat-sidebar-collapsed') === 'true'
   )
@@ -495,6 +513,7 @@ export default function AssistantChatPage() {
           setActiveQuestions(response.questions || [])
           setActiveActions(response.actions || [])
           setShowTaskLane(true)
+          setTaskLaneOwnerChatId(session.session_id)
         }
         // Refetch facts + active fix — the AI may have emitted markers.
         refreshSessionDerived(session.session_id)
@@ -509,17 +528,31 @@ export default function AssistantChatPage() {
   // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [])
 
-  // Persist task lane metadata to sessionStorage
+  // Render gate: the in-memory task-lane data is shown only when the chatId
+  // it belongs to (taskLaneOwnerChatId) matches activeChatId. Any path that
+  // flips activeChatId without clearing the lane state — in-place URL
+  // navigation, mid-flight pickup, HMR — produces a window where ownerChatId
+  // still tags the previous chat. The render gate keeps the lane hidden
+  // through that window until reset+repopulate runs for the new chat.
+  const taskLaneIsForActiveChat =
+    taskLaneOwnerChatId !== null && taskLaneOwnerChatId === activeChatId
+
+  // Persist task lane metadata to sessionStorage. The chatId field tags
+  // ownership — the chatId these questions/actions belong to, NOT the
+  // currently-active chat. Writing activeChatId here was the original bug:
+  // when activeChatId flipped to B but activeQuestions still had A's data,
+  // the snapshot stamped {chatId: B, questions: [A's]} and a subsequent
+  // restore would happily render A's data for B.
   useEffect(() => {
     try {
       sessionStorage.setItem('rf-tasklane-meta', JSON.stringify({
         show: showTaskLane,
-        chatId: activeChatId,
+        chatId: taskLaneOwnerChatId,
         questions: activeQuestions,
         actions: activeActions,
       }))
     } catch { /* ignore */ }
-  }, [showTaskLane, activeChatId, activeQuestions, activeActions])
+  }, [showTaskLane, taskLaneOwnerChatId, activeQuestions, activeActions])
 
   // Auto-scroll
   useEffect(() => {
@@ -575,6 +608,7 @@ export default function AssistantChatPage() {
     setShowTaskLane(false)
     setActiveQuestions([])
     setActiveActions([])
+    setTaskLaneOwnerChatId(null)
     setFacts([])
     setActiveFix(null)
     setPreviewKind(null)
@@ -615,7 +649,12 @@ export default function AssistantChatPage() {
       // Auto-open the task lane when the session has facts so the engineer
       // can see them — without this, a session with only facts (no open
       // questions) would hide the lane and the facts would be invisible.
-      if (list.length > 0) setShowTaskLane(true)
+      // Tag ownership too so the lane render gate accepts it as belonging
+      // to the active chat (the gate is `taskLaneOwnerChatId === activeChatId`).
+      if (list.length > 0) {
+        setShowTaskLane(true)
+        setTaskLaneOwnerChatId(chatId)
+      }
     } catch {
       // Best-effort — facts are accessory state. Surfacing a toast on every
       // refetch failure would be noisy; the empty state explains the absence.
@@ -788,7 +827,10 @@ export default function AssistantChatPage() {
       // TemplateMatchPanel is mounted inside TaskLane.bottomSlot, so the
       // lane must be visible for the panel to render. On fresh sessions
       // (no questions/facts) the lane defaults closed, so we open it here.
+      // Tag ownership to the current active chat so the lane render gate
+      // (taskLaneOwnerChatId === activeChatId) accepts it.
       setShowTaskLane(true)
+      if (activeChatId) setTaskLaneOwnerChatId(activeChatId)
       setScriptPanelOpen(true)
       return
     }
@@ -1055,6 +1097,7 @@ export default function AssistantChatPage() {
           setActiveQuestions(q)
           setActiveActions(a)
           setShowTaskLane(true)
+          setTaskLaneOwnerChatId(chatId)
         }
       }
     } catch {
@@ -1158,6 +1201,7 @@ export default function AssistantChatPage() {
         setActiveQuestions(response.questions || [])
         setActiveActions(response.actions || [])
         setShowTaskLane(true)
+        setTaskLaneOwnerChatId(sentForChatId)
       }
       // Phase 8: increment post-apply message counter for nudge logic.
       // Only increments when fix is still in 'proposed' (verifying) state —
@@ -1238,11 +1282,13 @@ export default function AssistantChatPage() {
         setActiveQuestions(response.questions || [])
         setActiveActions(response.actions || [])
         setShowTaskLane(true)
+        setTaskLaneOwnerChatId(sentForChatId)
       } else {
         // AI sent no new tasks — clear the lane
         setShowTaskLane(false)
         setActiveQuestions([])
         setActiveActions([])
+        setTaskLaneOwnerChatId(null)
       }
       // Phase 8: increment post-apply message counter for nudge logic (mirrors handleSend).
       // Only increments in 'proposed' (verifying) state — same rationale as handleSend.
@@ -1337,6 +1383,7 @@ export default function AssistantChatPage() {
         setActiveQuestions(response.questions || [])
         setActiveActions(response.actions || [])
         setShowTaskLane(true)
+        setTaskLaneOwnerChatId(session.session_id)
       }
       // Refetch facts + active fix — resume turn may emit markers.
       refreshSessionDerived(session.session_id)
@@ -1960,7 +2007,7 @@ export default function AssistantChatPage() {
                           <span className="hidden sm:inline">Paste Logs</span>
                         </button>
                       )}
-                      {!showTaskLane && (activeQuestions.length > 0 || activeActions.length > 0) && (
+                      {!showTaskLane && taskLaneIsForActiveChat && (activeQuestions.length > 0 || activeActions.length > 0) && (
                         <button
                           type="button"
                           onClick={() => setShowTaskLane(true)}
@@ -2033,6 +2080,7 @@ export default function AssistantChatPage() {
           Shows a count pill when new items are present while closed. */}
       {isNarrow
         && !showTaskLane
+        && taskLaneIsForActiveChat
         && (activeQuestions.length > 0 || activeActions.length > 0 || facts.length > 0 || activeFix !== null) && (
         <button
           onClick={() => setShowTaskLane(true)}
@@ -2054,7 +2102,7 @@ export default function AssistantChatPage() {
           Phase 2/3 make the lane the structural home of session diagnostic
           state, not a transient questions panel.
           Narrow viewport: the lane renders as a bottom drawer with backdrop. */}
-      {showTaskLane && (activeQuestions.length > 0 || activeActions.length > 0 || facts.length > 0 || activeFix !== null) && (
+      {showTaskLane && taskLaneIsForActiveChat && (activeQuestions.length > 0 || activeActions.length > 0 || facts.length > 0 || activeFix !== null) && (
         isNarrow ? (
           <div className="fixed inset-0 z-50 flex flex-col" role="dialog" aria-modal="true">
             <div