The agent loop signals silent replies (NO_REPLY, cancelled runs, suppressed
errors) by publishing an outbound message with empty content plus the inbound
routing metadata (placeholder_key / local_key). Slack, Telegram and Discord
each implement an empty-content branch in Send() that deletes their streamed
'Thinking...' placeholder — the partial draft left visible in the thread when
delivery is suppressed.
deliverOutbound skipped every text-only empty outbound, so that cleanup
signal never reached channel.Send and the stray partial draft stayed
published (issue #1475). Pass the signal through when placeholder routing
metadata is present; keep skipping bare empty messages so channels without
an empty-content branch never render empty bubbles.
Fixes#1475
fchengyan
4e99816a87