Add live roster / presence to A2ABus (announce + roster)#40
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Who is on a channel right now, gated by the same scopes as the messages: - announce(principal, channel) heartbeats a live seat; roster(channel, within=) lists subjects seen in the window, sorted. announce needs the channel's post scope (asserting presence is a write, so a read-only principal can't claim a seat); roster needs the read scope; denial stays opaque (who-is-here doesn't leak channel existence). - Presence is soft state: a subject that stops heartbeating ages off, and a roster seat is never a grant, so it can't smuggle access past the gate. An orchestrator can dispatch only to workers that are up and notice a dark one. - Backed by a per-channel presence table on the existing bus connection. 301 tests (+9), mypy --strict, ruff, catalog freshness all green. v1.7.0. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Live roster / presence (
A2ABus.announce/A2ABus.roster)Who is on a channel right now. The bus already answers "who may post/read here"; this adds "who is here", gated the same way:
announce(principal, channel)heartbeats a live seat and returns the timestamp — call it on a timer to stay live.roster(principal, channel, within=30.0)returns the subjects seen within the window, sorted.It reuses the auth core, it doesn't bolt on a side channel:
announceneeds the channel's post scope — asserting presence is a write, so a read-only watcher can't claim a seat it couldn't post from.rosterneeds the read scope, and denial stays opaque (an unknown channel and a declared-but-unauthorized one fail identically — who-is-here leaks channel existence no more than the messages do).That lets an orchestrator dispatch only to workers that are actually up, and notice when one goes dark — without a second identity system.
Backed by a per-channel
a2a_presencetable on the bus's existing connection.Verification
tests/test_presence.py— 9 tests: on-roster after announce, sorted+deduped, announce needs post scope, roster needs read scope, opaque denial, stale ages off, re-announce refreshes the heartbeat, per-channel isolation, decisions audited.mypy --strict,ruff, catalog freshness all green.Additive. Advances the "A2A depth: presence/live-roster" roadmap item.