fix: resolve race conditions in assistant/cockpit session loading

- Always load session data on mount even when urlSessionId matches
  activeChatId, fixing empty state after view toggle between /assistant
  and /cockpit (tasks/messages not showing until sidebar click)
- Add loadingRef for synchronous guards preventing duplicate sends,
  duplicate session creation, and prefill races
- Fix stale evidence_items closure in CockpitPage handlers
- Move setLoading(true) before first await in handlePrefill and
  handleResumeNew

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/hooks/useAssistantSession.ts

@@ -73,6 +73,8 @@ export function useAssistantSession() {
   const dragCounterRef = useRef(0)
   const prefillHandledRef = useRef(false)
   const currentChatRef = useRef<string | null>(activeChatId)
+  const loadingRef = useRef(false)
+  const initialLoadDoneRef = useRef(false)
 
   const toggleSidebarCollapse = () => {
     const next = !sidebarCollapsed
@@ -91,20 +93,22 @@ export function useAssistantSession() {
   // Load chat list on mount
   useEffect(() => { loadChats() }, [])
 
-  // If URL has a session ID, load it
+  // Load session data on mount or when URL session changes.
+  // On initial mount, always load even if activeChatId matches urlSessionId
+  // (state is empty after view toggle between /assistant and /cockpit).
   useEffect(() => {
-    if (urlSessionId && urlSessionId !== activeChatId) {
+    if (urlSessionId) {
-      selectChat(urlSessionId)
+      if (!initialLoadDoneRef.current || urlSessionId !== activeChatId) {
+        selectChat(urlSessionId)
+      }
+      initialLoadDoneRef.current = true
+    } else if (!initialLoadDoneRef.current && activeChatId) {
+      // Restore session from sessionStorage on mount (when URL has no session ID)
+      selectChat(activeChatId)
+      initialLoadDoneRef.current = true
     }
   }, [urlSessionId]) // eslint-disable-line react-hooks/exhaustive-deps
 
-  // Restore session from sessionStorage on mount (when URL has no session ID)
-  useEffect(() => {
-    if (!urlSessionId && activeChatId) {
-      selectChat(activeChatId)
-    }
-  }, []) // eslint-disable-line react-hooks/exhaustive-deps
-
   // Persist task lane metadata to sessionStorage
   useEffect(() => {
     try {
@@ -206,6 +210,8 @@ export function useAssistantSession() {
   }, [])
 
   const handleNewChat = async () => {
+    if (loadingRef.current) return
+    loadingRef.current = true
     try {
       const session = await aiSessionsApi.createChatSession({
         intake_type: 'free_text',
@@ -228,6 +234,8 @@ export function useAssistantSession() {
       setActiveActions([])
     } catch {
       toast.error('Failed to create chat')
+    } finally {
+      loadingRef.current = false
     }
   }
 
@@ -280,7 +288,8 @@ export function useAssistantSession() {
   const onTriageUpdateRef = useRef<((update: TriageUpdate) => void) | null>(null)
 
   const handleSend = async () => {
-    if (!input.trim() || !activeChatId || loading) return
+    if (!input.trim() || !activeChatId || loadingRef.current) return
+    loadingRef.current = true
 
     const sendChatId = activeChatId
     const userMessage = input.trim()
@@ -315,6 +324,7 @@ export function useAssistantSession() {
         { role: 'assistant', content: 'Sorry, something went wrong. Please try again.' },
       ])
     } finally {
+      loadingRef.current = false
       if (currentChatRef.current === sendChatId) {
         setLoading(false)
         requestAnimationFrame(() => inputRef.current?.focus())
@@ -333,9 +343,12 @@ export function useAssistantSession() {
     navigate(location.pathname, { replace: true, state: {} })
 
     const sendPrefill = async () => {
+      if (loadingRef.current) return
+      loadingRef.current = true
       setShowTaskLane(false)
       setActiveQuestions([])
       setActiveActions([])
+      setLoading(true)
 
       try {
         const session = await aiSessionsApi.createChatSession({
@@ -355,7 +368,6 @@ export function useAssistantSession() {
         setChats(prev => [chatItem, ...prev])
         setActiveChatId(prefillChatId)
         setMessages([{ role: 'user', content: prefill }])
-        setLoading(true)
 
         const response = await aiSessionsApi.sendChatMessage(prefillChatId, {
           message: prefill,
@@ -374,6 +386,7 @@ export function useAssistantSession() {
       } catch {
         toast.error('Failed to start AI conversation')
       } finally {
+        loadingRef.current = false
         setLoading(false)
       }
     }
@@ -401,6 +414,9 @@ export function useAssistantSession() {
   }
 
   const handleResumeNew = async (summary: string) => {
+    if (loadingRef.current) return
+    loadingRef.current = true
+    setLoading(true)
     try {
       const resumePrompt = `I'm continuing a previous troubleshooting session. Here's where we left off:\n\n${summary}\n\nPlease review this context and help me continue from where we stopped.`
       const session = await aiSessionsApi.createChatSession({
@@ -419,7 +435,6 @@ export function useAssistantSession() {
       setChats(prev => [chatItem, ...prev])
       setActiveChatId(session.session_id)
       setMessages([{ role: 'user', content: resumePrompt }])
-      setLoading(true)
 
       const resumeChatId = session.session_id
       const response = await aiSessionsApi.sendChatMessage(resumeChatId, { message: resumePrompt })
@@ -436,6 +451,7 @@ export function useAssistantSession() {
     } catch {
       toast.error('Failed to create resume chat')
     } finally {
+      loadingRef.current = false
       setLoading(false)
     }
   }
@@ -528,7 +544,7 @@ export function useAssistantSession() {
     handleFileSelect, handleRemoveUpload, retryUpload,
     toggleSidebarCollapse, handlePrefill, processResponse,
     // Refs
-    messagesEndRef, inputRef, fileInputRef, currentChatRef,
+    messagesEndRef, inputRef, fileInputRef, currentChatRef, loadingRef,
     // Page-specific callbacks
     onSessionLoadedRef, onTriageUpdateRef,
     // Constants

frontend/src/pages/CockpitPage.tsx

@@ -99,20 +99,26 @@ export default function CockpitPage() {
 
   const handleEvidenceAdd = useCallback(async (text: string, status: EvidenceItem['status']) => {
     const newItem: EvidenceItem = { text, status }
-    const updated = [...triageMeta.evidence_items, newItem]
+    let updated: EvidenceItem[] = []
-    setTriageMeta(prev => ({ ...prev, evidence_items: updated }))
+    setTriageMeta(prev => {
+      updated = [...prev.evidence_items, newItem]
+      return { ...prev, evidence_items: updated }
+    })
     if (session.activeChatId) {
       try { await aiSessionsApi.updateTriage(session.activeChatId, { evidence_items: updated }) } catch { /* best-effort */ }
     }
-  }, [session.activeChatId, triageMeta.evidence_items])
+  }, [session.activeChatId])
 
   const handleEvidenceEdit = useCallback(async (index: number, text: string, status: EvidenceItem['status']) => {
-    const updated = triageMeta.evidence_items.map((item, i) => i === index ? { text, status } : item)
+    let updated: EvidenceItem[] = []
-    setTriageMeta(prev => ({ ...prev, evidence_items: updated }))
+    setTriageMeta(prev => {
+      updated = prev.evidence_items.map((item, i) => i === index ? { text, status } : item)
+      return { ...prev, evidence_items: updated }
+    })
     if (session.activeChatId) {
       try { await aiSessionsApi.updateTriage(session.activeChatId, { evidence_items: updated }) } catch { /* best-effort */ }
     }
-  }, [session.activeChatId, triageMeta.evidence_items])
+  }, [session.activeChatId])
 
   const handleStepComplete = useCallback((index: number) => {
     setCompletedSteps(prev => {

frontend/src/pages/FlowPilotPage.tsx

@@ -20,7 +20,7 @@ export default function FlowPilotPage() {
   }, []) // eslint-disable-line react-hooks/exhaustive-deps
 
   const handleTaskSubmit = async (responses: Array<{ type: string; state: string; value: string; text?: string; label?: string }>) => {
-    if (!session.activeChatId || session.loading) return
+    if (!session.activeChatId || session.loading || session.loadingRef.current) return
 
     const parts: string[] = []
     for (const r of responses) {