Cross-connection DMs were pure polling: the Desktop drains every gateway's
bot_relay outbox on a 4s interval, so each hop eats up to 4s outbound plus
4s for the reply leg (#92760 'bots reply slowly').
Emission point: the gateway's existing change watcher (_CHANGE_WATCHES in
tui_gateway/server.py). Envelopes are written by the AGENT process
(message_agent -> tools.bot_relay.enqueue_envelope), not the gateway, so no
gateway RPC is on the enqueue path and an in-process emit is impossible.
That is exactly the situation the change watcher already solves for the
pairing store (pairing.changed: 'written by a different process; the files
are the only shared signal') - so a new bot_relay.outbox.pending entry in
the existing watch table is the smallest correct diff: one cheap 1s-interval
stat probe folded into the existing 0.5s watcher tick, no new thread, no new
RPC, and _broadcast_global_event fans it to every connected WS client for
free. The signature is monotone (newest envelope mtime ever seen) so a
drain emptying outbox/ never re-fires the event.
Desktop (hermes-bots plugin): subscribe via the existing host.onEvent tap
(feature-detected - older shells lack it) and run drainRelayOutboxes through
a 250ms trailing debounce so a burst of signals collapses to one drain.
The 4s interval poll is intentionally UNCHANGED as the backstop: the event
tap only hears the active gateway socket, so per-connection push detection
would be complex and wrong to trade the poll against - push simply makes
the common case near-instant while older backends keep working exactly as
before.
Tests: 3 new watcher contracts (fires on enqueue, monotone across drain,
silent with no outbox) and a new relay-push-drain.test.mjs (debounce burst
-> one drain, re-arm after window, disposed no-op, poll backstop intact).
kshitijk4poor
9c829f965d