fix(desktop): revoke optimistic blob previews when the consumer is discarded or replaced

Completes the #63682 ownership handoff flagged in review on #66546: the
queued-prompt side revoked discarded blob: previews, but the optimistic
bubble's previews were never released. Revoke when the optimistic message
is dropped (unless a rejected-submit restore re-loaded the attachments
into the composer, which re-owns them) and when the post-sync rewrite
replaces blob: refs with workspace-resolvable ones.

Co-authored-by: stantheman0128 <stanshih888@gmail.com>

apps/desktop/src/app/session/hooks/use-prompt-actions/submit.ts

@@ -18,6 +18,7 @@ import {
   $composerAttachments,
   type ComposerAttachment,
   mainComposerScope,
+  revokeDiscardedAttachmentPreviews,
   terminalContextBlocksFromDraft
 } from '@/store/composer'
 import { $hudMode } from '@/store/hud'
@@ -487,7 +488,11 @@ export function useSubmitPrompt(deps: SubmitPromptDeps) {
 
       // After sync rewrites refs, refresh the optimistic message in place so the
       // transcript shows the resolved @file: ref rather than the local path.
-      const rewriteOptimistic = (sid: string) =>
+      // Sync replaces blob: previews with workspace-resolvable refs, so any
+      // blob: URL the rewritten refs no longer retain is this consumer's last
+      // reference — release it (#63682 ownership handoff).
+      const rewriteOptimistic = (sid: string, syncedAttachments: ComposerAttachment[] = attachments) => {
+        revokeDiscardedAttachmentPreviews(attachments, syncedAttachments)
         updateSessionState(
           sid,
           state => ({
@@ -496,8 +501,13 @@ export function useSubmitPrompt(deps: SubmitPromptDeps) {
           }),
           targetStoredSessionId
         )
+      }
 
       const dropOptimistic = (sid: null | string) => {
+        // The optimistic bubble is gone, so its blob: previews die with it —
+        // unless a rejected-submit restore already re-loaded the attachments
+        // into the composer, which re-owns those URLs (#63682 handoff).
+        revokeDiscardedAttachmentPreviews(attachments, usingComposerAttachments ? $composerAttachments.get() : [])
         if (!sid) {
           if (targetIsCurrentView()) {
             scope.setMessages(current => current.filter(m => m.id !== optimisticId))
@@ -811,7 +821,7 @@ export function useSubmitPrompt(deps: SubmitPromptDeps) {
         // the gateway receives @file: paths that resolve in its workspace.
         // Images keep their inline bounded thumbnail — see optimisticAttachmentRef.
         attachmentRefs = syncedAttachments.map(optimisticAttachmentRef).filter((r): r is string => Boolean(r))
-        rewriteOptimistic(liveSessionId)
+        rewriteOptimistic(liveSessionId, syncedAttachments)
         const text = buildContextText(syncedAttachments)
 
         // Another Desktop window may own a newer transcript while this one