[iamnbutler]

Part of #607. In a teammate's channel whose Mac was offline, the composer offered Ace mode and pre-filled an "ace" chip while agent access was unknown.

The composer now offers agent mode only to the channel's owner, or to a teammate once the channel reports that agent access is on. While access is unknown, it shows Chat only, with the placeholder "Message the channel" and no ace mention. The saved per-channel mode is unchanged, so the person's choice comes back once access is known. Known-off keeps "Message the channel (agent access is off)" from #612.

The study's "reverts to Ace mode after reload" isn't changed here. The mode is already saved per channel in localStorage, and each tester turn used a fresh browser.

Smoke: isolated loopback host on port 4771 from this lane, rebuilt app, with samchan created as ACE_USER=sam so the browser is a teammate there.

• Access off: Chat only, "Message the channel (agent access is off)".
• After ace agents samchan on: Ace mode with the ace chip and the model picker.
• Unknown: I froze samchan's worker with SIGSTOP and opened it in a fresh browser. The composer showed Chat only, "Message the channel", with no chip.
• Owner's own channel: Ace mode by default, as before.

I didn't reproduce this with a real offline second Mac. The frozen worker leaves shared unknown in the same way.

Built in Ace

No. Built by Claude Code as a fix worker after the two-Mac pair study because the worker runs outside an Ace channel. Dogfooding gap tracked in #5.