fix(pilot): Phase 9 review — partial-outcome notes + per-fix script-builder remount

Addresses docs/FlowAssist_Migration/Issues/phase-9-review-issues.md.

Issue #1 (High): "Applied partially" from the escalation intercept silently
dropped because the backend requires notes on applied_partial and the dialog
sent none. The catch was silent and the UI advanced into the conclude flow
as if the outcome were recorded.
- EscalateInterceptDialog now has a two-step flow: clicking the partial
  choice reveals a notes textarea (autofocused, required non-empty) plus
  Back / "Record partial & escalate" buttons.
- onChoose signature extended to (choice, notes?).
- handleInterceptChoice passes notes to patchOutcome; on failure it
  surfaces a toast and does NOT advance to the conclude modal, so the
  intercept stays open for retry.

Issue #2 (Medium/High): ScriptBuilderTab kept local state across active-fix
changes within the same pilot session, so a stale draft could PATCH against
a newer fix.id. Added key={activeFix.id} on the mount — forces a clean
remount per fix; backend get-or-create (keyed on user+ai_session_id) still
returns the same session row, which is the intended resume-on-refresh
semantic; but messages/editorBuffer/latestScript local state resets.

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

frontend/src/pages/AssistantChatPage.tsx

@@ -656,19 +656,33 @@ export default function AssistantChatPage() {
     setShowConclude(true)
   }, [activeFix])
 
-  const handleInterceptChoice = useCallback(async (choice: InterceptChoice) => {
+  const handleInterceptChoice = useCallback(async (choice: InterceptChoice, notes?: string) => {
     const stored = escalateIntercept
-    setEscalateIntercept(null)
-    if (!stored || !activeChatId) return
+    if (!stored || !activeChatId) {
+      setEscalateIntercept(null)
+      return
+    }
     const outcomeToSend: FixOutcome =
       choice === 'never_applied' ? 'dismissed' : choice
     try {
       const updated = await sessionSuggestedFixesApi.patchOutcome(
-        activeChatId, stored.fixId, outcomeToSend,
+        activeChatId, stored.fixId, outcomeToSend, notes,
       )
       setActiveFix(updated)
-    } catch { /* non-fatal — engineer can still escalate */ }
-    setShowConclude(true)
+      setEscalateIntercept(null)
+      setShowConclude(true)
+    } catch (err) {
+      // applied_partial without notes (or any other 4xx) must surface — the
+      // previous silent catch let engineers believe the partial outcome was
+      // recorded while it was rejected server-side.
+      const message = choice === 'applied_partial'
+        ? 'Couldn’t record the partial outcome. Add a short note and try again.'
+        : 'Couldn’t record the outcome before escalating. Try again.'
+      toast.error(message)
+      // Keep the intercept open so the engineer can retry (partial path can
+      // re-enter the notes step from the dialog).
+      if (import.meta.env.DEV) console.warn('[AssistantChat] intercept outcome failed:', err)
+    }
   }, [activeChatId, escalateIntercept])
 
   // Phase 8: Resolve click — auto-mark applied_success if in verifying state
@@ -1629,7 +1643,12 @@ export default function AssistantChatPage() {
                 so both scroll positions and state are preserved across tab switches. */}
             {showTabStrip && activeFix && activeChatId && (
               <div className={cn('flex-1 min-h-0 flex flex-col', chatTab !== 'script_builder' && 'hidden')}>
+                {/* key={activeFix.id} forces a fresh mount when the active
+                    fix changes within the same pilot session — otherwise
+                    stale messages / editorBuffer / latestScript from the
+                    prior fix could submit against the new fix.id. */}
                 <ScriptBuilderTab
+                  key={activeFix.id}
                   fix={activeFix}
                   pilotSessionId={activeChatId}
                   onProgressChange={setScriptBuilderHasProgress}