fix: close relay loop from prefixed dedup mismatch

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>

host-bridge/bridge_core.py

@@ -56,5 +56,21 @@ class MessageBus:
             self._seen[h] = now + self._dedup_ttl
             return False
 
+    def mark_seen(self, text: str) -> None:
+        """Record text as already-seen without reporting duplicate status.
+
+        The dispatcher relays a *prefixed* copy of each message (e.g.
+        "[meshtastic/x] hello"), not the original text. Dedup is content-hash
+        based, so unless the exact on-air relayed string is recorded here, the
+        bridge won't recognise its own relayed copy when it echoes back from
+        another network — it would re-relay it, stacking another prefix each
+        hop (an unbounded loop). Marking every outbound string seen closes
+        that loop.
+        """
+        h = self._content_hash(text)
+        now = time.monotonic()
+        with self._lock:
+            self._seen[h] = now + self._dedup_ttl
+
     def get(self, timeout: float | None = None) -> BridgeMessage:
         return self._queue.get(timeout=timeout)

host-bridge/main.py

@@ -82,11 +82,16 @@ def main() -> int:
             if bus.is_duplicate(message.text):
                 continue
             print(f"[{message.network}] {message.sender}: {message.text}")
+            relayed = f"[{message.network}/{message.sender}] {message.text}"
+            # Record the exact on-air string so that if this relayed copy is
+            # re-heard from another network it's recognised as a duplicate and
+            # not re-relayed (which would stack another prefix each hop).
+            bus.mark_seen(relayed)
             for network, adapter in adapters.items():
                 if network == message.network:
                     continue  # don't echo back onto the network it came from
                 try:
-                    adapter.send(f"[{message.network}/{message.sender}] {message.text}")
+                    adapter.send(relayed)
                 except Exception as exc:  # noqa: BLE001
                     print(f"  ! failed to relay onto {network}: {exc}", file=sys.stderr)
     except KeyboardInterrupt: