fix(frontend): interrupt-promotion on deferred prompts + queue UX

frontend/src/components/common/RobustPromptInput.tsx

@@ -596,6 +596,22 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
     pinPrompt,
   } = usePromptHistory({ sessionId, specTaskId, projectId, apiClient })
 
+  // Canonical "still actionable in the queue" list, failed-first. Computed in ONE
+  // place so every consumer — queue display, the interrupt toggle, the empty-Enter
+  // interrupt-promotion, the client-side pump — operates on the SAME set.
+  // Previously each site recomputed [...failedPrompts, ...pendingPrompts]
+  // independently, and the promotion path diverged to pendingPrompts-only — so it
+  // silently skipped a prompt the instant the backend deferred it to 'failed'
+  // (which a long current turn does almost immediately).
+  //
+  // We exclude 'sending' (backend has dispatched to Zed, awaiting first
+  // message_added): once a message is in flight it can't be promoted/toggled, and
+  // showing it in the queue until the *next* sync flips it to 'sent' is the lag
+  // that makes a just-sent prompt linger. Dropping 'sending' hides it optimistically
+  // the moment dispatch is confirmed; if it later bounces it returns via 'failed'.
+  // See design/2026-06-19-incident-interrupt-during-boot-context-loss.md.
+  const queuedPrompts = [...failedPrompts, ...pendingPrompts].filter(p => p.status !== 'sending')
+
   // Track previous appendText to detect changes
   const prevAppendTextRef = useRef<string | undefined>(undefined)
 
@@ -621,7 +637,7 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
     if (processingRef.current || !isOnline || disabled) return
 
     // Interrupt-mode messages first, then queue-mode, each oldest-first.
-    const sortedQueue = [...failedPrompts, ...pendingPrompts].sort((a, b) => {
+    const sortedQueue = [...queuedPrompts].sort((a, b) => {
       const aInterrupt = a.interrupt !== false
       const bInterrupt = b.interrupt !== false
       if (aInterrupt && !bInterrupt) return -1
@@ -659,7 +675,7 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
       setSendingId(null)
       processingRef.current = false
     }
-  }, [backendQueueEnabled, isOnline, disabled, failedPrompts, pendingPrompts, sendingId, editingId, onSend, markAsSent, markAsFailed])
+  }, [backendQueueEnabled, isOnline, disabled, queuedPrompts, sendingId, editingId, onSend, markAsSent, markAsFailed])
 
   // Pump the queue when messages are pending and we're online.
   useEffect(() => {
@@ -750,7 +766,7 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
   }, [draft, adjustHeight])
 
   // Notify parent when queue changes (affects overall height)
-  const queueLength = pendingPrompts.length + failedPrompts.length
+  const queueLength = queuedPrompts.length
   useEffect(() => {
     if (onHeightChange) {
       // Small delay to allow Collapse animation to start
@@ -820,11 +836,11 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
 
   // Toggle interrupt mode for a queued message
   const handleToggleInterrupt = useCallback((entryId: string) => {
-    const entry = [...failedPrompts, ...pendingPrompts].find(e => e.id === entryId)
+    const entry = queuedPrompts.find(e => e.id === entryId)
     if (entry) {
       updateInterrupt(entryId, entry.interrupt === false)
     }
-  }, [failedPrompts, pendingPrompts, updateInterrupt])
+  }, [queuedPrompts, updateInterrupt])
 
   // Restart Zed thread after a Claude Agent crash. Calls the backend endpoint
   // which clears the dead acp_thread_id and resets crashed prompts back to
@@ -938,7 +954,10 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
       // Empty field: promote most-recent queued entry to interrupt instead of sending nothing.
       if (!content && attachments.length === 0) {
         if (disabled) return
-        const candidates = pendingPrompts.filter(p =>
+        // Promote the most-recent NON-interrupt queued message to interrupt.
+        // Scans queuedPrompts (failed + pending) so a deferred message — the one
+        // the user is actually trying to escalate — is still a candidate.
+        const candidates = queuedPrompts.filter(p =>
           p.interrupt === false &&
           !p.deleted &&
           p.id !== sendingId &&
@@ -998,7 +1017,7 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
         e.preventDefault()
       }
     }
-  }, [draft, disabled, attachments, saveToHistory, clearDraft, navigateUp, navigateDown, pendingPrompts, updateInterrupt, sendingId, editingId])
+  }, [draft, disabled, attachments, saveToHistory, clearDraft, navigateUp, navigateDown, queuedPrompts, updateInterrupt, sendingId, editingId])
 
   // Add a file as an attachment (queues for upload, uploads if online)
   const addFileAsAttachment = useCallback((file: File): string => {
@@ -1219,7 +1238,7 @@ const RobustPromptInput: FC<RobustPromptInputProps> = ({
   }
 
   // All queued messages (pending + failed), sorted: interrupt mode first, then queue mode
-  const queuedMessages = [...failedPrompts, ...pendingPrompts].sort((a, b) => {
+  const queuedMessages = [...queuedPrompts].sort((a, b) => {
     // Interrupt mode (true or undefined) comes first
     const aInterrupt = a.interrupt !== false
     const bInterrupt = b.interrupt !== false

frontend/src/hooks/usePromptHistory.ts

@@ -209,9 +209,19 @@ export function usePromptHistory({
       // IDs that are locally tombstoned — never re-import these from backend
       const deletedIds = new Set(prev.filter(e => e.deleted).map(e => e.id))
 
-      // Mark existing entries that are in backend as synced (skip deleted ones)
+      // Mark existing entries that are in backend as synced (skip deleted ones).
+      // CRITICAL: never re-confirm an entry that has an un-pushed local change
+      // (syncedToBackend === false, set by updateInterrupt/updateContent). A pull
+      // confirms the backend has *some* version, not the local one — flipping a
+      // dirty entry back to "synced" makes the next syncToBackend skip it, so the
+      // local change is silently dropped. This is exactly how promoting a queued
+      // prompt to interrupt showed the lightning in the UI while the backend kept
+      // interrupt=false: a backend poll landed between the promote and the push.
+      // See design/2026-06-19-incident-interrupt-during-boot-context-loss.md.
       const updatedPrev = prev.map(e =>
-        backendIds.has(e.id) && !e.deleted ? { ...e, syncedToBackend: true } : e
+        backendIds.has(e.id) && !e.deleted && e.syncedToBackend !== false
+          ? { ...e, syncedToBackend: true }
+          : e
       )
 
       // Add any backend entries that don't exist locally (mark as synced)
@@ -443,7 +453,10 @@ export function usePromptHistory({
                   retryCount: backendEntry.retryCount,
                   nextRetryAt: backendEntry.nextRetryAt,
                   errorMessage: backendEntry.errorMessage,
-                  syncedToBackend: true
+                  // Reflect backend-owned status, but PRESERVE a pending local
+                  // change (e.g. an interrupt promotion not yet pushed) — don't
+                  // clobber the dirty flag, or syncToBackend will skip the push.
+                  syncedToBackend: h.syncedToBackend === false ? false : true,
                 }
               }
               // Reconcile against the source of truth: a queue entry we previously