The dispatcher deduped on inbound text but relayed a prefixed copy
("[net/sender] text"), so a re-heard relayed message hashed differently
and was re-relayed, stacking another prefix each hop — an unbounded loop,
exactly what the dedup was meant to prevent.
Add MessageBus.mark_seen() and record the on-air relayed string before
sending, so the bridge recognises and drops its own relayed copies.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
