fix(pilot): wipe full task-lane state on chat switch + extract palette event

Two fixes from the Phase 5 shakedown:

1. Stale lane data leaking across chats. handleNewChat, sendPrefill, and
   handleResumeNew were each missed when Phase 3/5 added activeFix,
   previewKind, previewData, and scriptPanelOpen — only selectChat reset
   the full set. Result: starting a new chat while a Suggested Fix card
   was active showed the previous session's fix card (and any open
   preview/script panel) until the next backend refresh swept it.
   Consolidated all four entry points behind a single
   resetSessionDerivedState() helper so adding new lane state in future
   phases only requires touching one place.

2. CommandPalette TDZ on cold load. SCRIPTS_INLINE_QUICK_ACTION (line 66)
   referenced PILOT_INLINE_SCRIPT_PATH declared at line 94 — module-level
   evaluation hit the use before the declaration. Browser blanked with
   "Cannot access 'PILOT_INLINE_SCRIPT_PATH' before initialization".
   Moved the path const above its first use; also extracted
   PILOT_INLINE_SCRIPT_EVENT into a tiny @/lib/pilotEvents module so
   AssistantChatPage doesn't import the palette component just to read a
   string — that mixed-export pattern broke Fast Refresh ("consistent
   components exports") and added an unnecessary import edge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/pages/AssistantChatPage.tsx

@@ -18,7 +18,7 @@ import { SuggestedFix } from '@/components/pilot/sections/SuggestedFix'
 import { ResolutionNotePreview as ResolutionNotePreviewPopover } from '@/components/pilot/ResolutionNotePreview'
 import { TemplateMatchPanel } from '@/components/pilot/script/TemplateMatchPanel'
 import { NoTemplateDialog } from '@/components/pilot/script/NoTemplateDialog'
-import { PILOT_INLINE_SCRIPT_EVENT } from '@/components/layout/CommandPalette'
+import { PILOT_INLINE_SCRIPT_EVENT } from '@/lib/pilotEvents'
 import { sessionFactsApi, type SessionFact } from '@/api/sessionFacts'
 import {
   sessionSuggestedFixesApi,
@@ -163,9 +163,7 @@ export default function AssistantChatPage() {
 
     const sendPrefill = async () => {
       // Clear stale task lane from previous session
-      setShowTaskLane(false)
-      setActiveQuestions([])
-      setActiveActions([])
+      resetSessionDerivedState()
       setActiveSessionStatus('active')
       setActivePsaTicketId(null)
 
@@ -274,6 +272,24 @@ export default function AssistantChatPage() {
     }
   }
 
+  // Single source of truth for "wipe every per-session task-lane state field"
+  // before switching to a different chat. Called from selectChat, handleNewChat,
+  // sendPrefill, and handleResumeNew so adding new lane-scoped state in future
+  // phases only requires touching this one helper. Forgetting to clear a field
+  // leaks the previous session's data into the new one (Phase 5 regression).
+  const resetSessionDerivedState = useCallback(() => {
+    setShowTaskLane(false)
+    setActiveQuestions([])
+    setActiveActions([])
+    setFacts([])
+    setActiveFix(null)
+    setPreviewKind(null)
+    setPreviewData(null)
+    setPreviewError(null)
+    setPreviewPosting(false)
+    setScriptPanelOpen(false)
+  }, [])
+
   // Phase 2 facts — fetch + handlers. `refreshFacts` is called from selectChat
   // and after each chat send, because the AI may have emitted [PROMOTE] markers
   // that synthesized new facts server-side (see unified_chat_service.
@@ -503,17 +519,9 @@ export default function AssistantChatPage() {
     currentChatRef.current = chatId
     setActiveChatId(chatId)
     // Clear TaskLane when switching chats — will restore from backend if available
-    setShowTaskLane(false)
-    setActiveQuestions([])
-    setActiveActions([])
+    resetSessionDerivedState()
     setActiveSessionStatus(null)
     setActivePsaTicketId(null)
-    setFacts([])
-    setActiveFix(null)
-    setPreviewData(null)
-    setPreviewError(null)
-    setPreviewKind(null)
-    setScriptPanelOpen(false)
     // Fire facts + active-fix fetches in parallel with session detail.
     refreshSessionDerived(chatId)
     try {
@@ -558,12 +566,8 @@ export default function AssistantChatPage() {
     // for the previous session sees a mismatch and bails — prevents stale task lane appearing
     // in the new empty session (same pattern as selectChat, which sets ref before its await).
     currentChatRef.current = null
-    // Clear stale state immediately — don't wait for API to return
-    setShowTaskLane(false)
-    setActiveQuestions([])
-    setActiveActions([])
-    setFacts([])
-    setScriptPanelOpen(false)
+    // Clear stale state immediately — don't wait for API to return.
+    resetSessionDerivedState()
     setMessages([])
     setActiveSessionStatus('active')
     setActivePsaTicketId(null)
@@ -763,10 +767,8 @@ export default function AssistantChatPage() {
   const handleResumeNew = async (summary: string) => {
     // Invalidate currentChatRef BEFORE the await — same guard as handleNewChat
     currentChatRef.current = null
-    // Clear stale state immediately — don't wait for API to return
-    setShowTaskLane(false)
-    setActiveQuestions([])
-    setActiveActions([])
+    // Clear stale state immediately — don't wait for API to return.
+    resetSessionDerivedState()
     setActiveSessionStatus('active')
     setActivePsaTicketId(null)
     try {