Phase 668: composer embed prefetch IPC routes.

Wire composer-embed-prefetch and composer-embed-preview-clear to platform.

Co-authored-by: Cursor <[email protected]>

README.md

@@ -2,6 +2,8 @@
 
 Pearcord desktop UI IPC dispatch and automated flow scenarios for Bare smokes. Mirrors `apps/pearcord` pear-pipe message handling.
 
+**Phase 668 (v0.8.643):** IPC `composer-embed-prefetch` → platform `prefetchComposerEmbed`; `composer-embed-preview-clear` → `clearComposerEmbedPreview`. Bundle: `npm run test:ci-phase668`.
+
 **Phase 665 batch 2 (v0.8.640):** IPC `cancel-attachment-download`, `forward-attachment`, `open-attachment-in-viewer`; download progress polling via `attachment-download-progress` event. Bundle: `npm run test:phase665-media-batch2`.
 
 **v0.8.638 (Phase 659):** Added DM poll IPC routes: `vote-dm-poll` (optional `voted` desired-state) -> `dm-poll-voted`, `edit-dm-poll` -> `dm-poll-edited`, `close-dm-poll` -> `dm-poll-closed`, and `delete-dm-poll` -> `dm-poll-deleted`.

index.js

@@ -2414,6 +2414,16 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     platform.setComposerImeComposing(!!msg.active)
     return true
   }
+  if (t === 'composer-embed-prefetch') {
+    await platform.prefetchComposerEmbed(msg.url)
+    pushState()
+    return true
+  }
+  if (t === 'composer-embed-preview-clear') {
+    platform.clearComposerEmbedPreview()
+    pushState()
+    return true
+  }
   if (t === 'retry-link-embed') {
     await platform.retryLinkEmbedForMessage(msg.messageId)
     pushState()