Teknium af3d5150c1 fix(matrix): close 'hall of mirrors' pairing + echo loop (#15763) (#16374) ...

Harden the Matrix adapter's sender-drop guards so bot-self events and
appservice/bridge identities never reach the gateway's pairing flow or
the agent loop.

Two filters, applied as early as possible in _on_room_message (and
_on_reaction for the self-filter):

1. _is_self_sender(sender) — case-insensitive + whitespace-trimmed
   equality with self._user_id.  When self._user_id is still empty
   (whoami has not resolved, or login failed), returns True
   defensively: an unidentified bot dropping its own events is always
   preferable to falling into an echo loop.  The previous byte-for-byte
   equality check let differently-cased copies of the bot's MXID slip
   through, and an unresolved self-ID silently disabled the guard.

2. _is_system_or_bridge_sender(sender) — drops appservice namespace
   puppets (conventional @_bridge_...:server form) and malformed
   senders with an empty localpart.  These identities used to fall
   through to the gateway's unauthorized-user path, trigger a pairing
   code, and — once an operator approved the bridge — every outbound
   message the bridge relayed would loop back as an authorized user
   message.  This was the root of the 'hall of mirrors' symptom.

Fixes #15763

Test plan
---------
scripts/run_tests.sh tests/gateway/test_matrix.py
scripts/run_tests.sh tests/gateway/test_matrix_mention.py tests/gateway/test_matrix_voice.py
All 182 tests pass.  14 new regression tests cover exact / case-insensitive
/ whitespace / unresolved-self-id matches, bridge prefix detection, empty
sender, and the full _on_room_message drop path.

2026-04-26 21:50:28 -07:00

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