When the Matrix homeserver returns M_UNKNOWN_TOKEN / M_FORBIDDEN /
M_UNAUTHORIZED (or soft_logout), the previous _sync_loop kept retrying
sync_forever every 2 seconds forever, spamming the homeserver and
filling logs (#1851). The auth state cannot recover by retrying, so
this is pure noise and a soft DoS on the homeserver.
- Extract `_is_fatal_auth_response()` helper
- In `_on_sync_error`, on fatal auth: set `_running=False` and call
`stop_sync_forever()` so the loop exits cleanly
- Add exponential backoff (2s → 60s cap) to the generic exception path
in `_sync_loop` so transient network blips also stop hammering
Closes#1851
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Matrix sync replays the room timeline on each startup or `/restart`,
causing already-handled messages to be reprocessed (#3553). Even with
`store_sync_tokens=True`, the sync token isn't reliably re-injected
when restoring a session via access_token + load_store(), so the
client re-reads recent timeline entries.
Filter `event.server_timestamp` against the process start time so old
events are dropped at the `_on_message` / `_on_media_message` entry
points. Trade-off: messages received during downtime won't be
processed, which matches the issue reporter's expectation.
Closes#3553
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
