feat(ui-flow): composer focus after thread/forum create (Phase 443)

Send composer-focus-channel IPC after create-thread and create-forum-post
so the message composer autofocuses in the new thread.

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

README.md

@@ -108,6 +108,16 @@ await dispatchUiMessage(
 
 **v0.8.174:** `update-guild-settings` IPC forwards `nsfwGateEnabled` to `platform.updateGuildSettings`.
 
+## Composer focus channel (v0.8.406)
+
+After `create-thread` or `create-forum-post`, dispatch emits a sidecar event (not a full IPC round-trip from the UI):
+
+```javascript
+send({ type: 'composer-focus-channel', channelId: thread.id })
+```
+
+The renderer handles `composer-focus-channel` and calls `requestComposerAutofocusForChannel(channelId)` so the message box focuses once the new thread/post channel is active. Smoke: `test:composer-autofocus-after-thread-create`. See [MESSAGE_THREADS.md](../../docs/MESSAGE_THREADS.md) and [FORUM_CHANNELS.md](../../docs/FORUM_CHANNELS.md).
+
 ## Maintenance
 
 When adding IPC in the Pear app, add the same `msg.type` branch here first (or simultaneously) so `dispatchUiMessage` remains the single routing table.

index.js

@@ -859,17 +859,20 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     return true
   }
   if (t === 'create-thread') {
-    await platform.createThread({ messageId: msg.messageId, name: msg.name })
+    const thread = await platform.createThread({ messageId: msg.messageId, name: msg.name })
     pushState()
+    send({ type: 'composer-focus-channel', channelId: thread.id })
     return true
   }
   if (t === 'create-forum-post') {
-    await platform.createForumPost({
+    const result = await platform.createForumPost({
       title: msg.title,
       content: msg.content,
       tags: msg.tags
     })
     pushState()
+    const threadId = result?.thread?.id
+    if (threadId) send({ type: 'composer-focus-channel', channelId: threadId })
     return true
   }
   if (t === 'set-forum-channel-palette') {