Friend DM never sends presence: turn.start has no trigger, so no 'is thinking…' for DM replies (#297 follow-up) #332

Summary

In a friend DM, the replying home never sends the presence signal, so the asker never sees Name is thinking… while the friend's Bot works. Bot Social prod lists presence in GET /v1/platform features, and the face-room case works (the line shows there). Follow-up to #297 / #301 (DM half).

Cause (found with a debug log, not a debugger)

createPresence().onTurnStart (plugins/social/src/presence.js) takes targetOf(event), whose DM branch needs event.place === 'chat' && event.trigger?.from?.kind === 'remote'. In a live friend DM the turn.start event of the answering Bot has place: 'chat', a botId and a turnId, but no trigger field. targetOf returns undefined, onTurnStart returns early, and set_presence is never called (no beat ok / beat err either). The core feed (core/src/host/flybot-feed.js) fills trigger from entry.pending, which only the preceding user/message event sets (deliveredOf); for a friend's line that delivered record is evidently missing or comes after turn/start.

Repro (main a526c75, Node 24, Bot Social prod with presence)

1. Two fresh homes A and B (own DSH_HOME each, ports e.g. 3101/3102), both with a working model, flybot-social pointed at the Bot Social server.
2. A: Chief → Sharing → Invite to this Bot. B: Add friend → paste the link. Wait about 20 s for the grant to sync (a message sent right after joining is refused, see Accepting an invite briefly publishes the joiner's (unshared) Bot on the inviter's home: dead 'no longer shared with you' chat opens on load; friend invisible in Social #303).
3. B opens "A's Chief" and sends a line (for example "Name a tea house near West Lake").
4. While A's Chief works, poll B's flybot/social/typing (or watch B's chat): {"supported":true,"typing":[]} the whole time, and no is thinking… line.
5. To see the cause: log the event in onTurnStart on A. It prints {"place":"chat","botId":"session-…","turnId":"session-…#2"} with no trigger.

Expected

turn.start for a turn answering a friend's line carries trigger.from.kind === 'remote' with the friend's handle (or targetOf finds the friend another way, for example the Bot's open remote chat), so set_presence { to } goes out and B shows Name is thinking… until the reply or the held-approval line arrives.

Notes

• README (PR docs(readme): re-record every demo on the current UI #329) now says the thinking line shows in face rooms and that the DM one is not shown yet.
• Unit tests in plugins/social/test/presence.test.js feed targetOf a hand-built event with trigger, so they pass without the real feed shape. A live or feed-level test would catch this.