Mattermost `_find_existing_bot` swallows all exceptions and reports the bot as missing

_find_existing_bot in core/switch_core/bridges/collaboration/mattermost/adapter.py (lines 1643-1663) wraps its entire paged lookup in except Exception: pass and returns None.

A session expiry, a 500 from Mattermost, a network blip or a malformed page all collapse into the same None. Both callers (lines 973 and 1125) read that as "this bot does not exist yet" and respond by creating the bot. The create then fails with a username-taken error, and the logs show "Failed to create Mattermost bot" — the real cause, that the lookup failed, is never recorded anywhere. Nothing is logged in the swallow itself.

This is a "Fail Loud, Never Fake" violation: an error path returns a plausible-looking value the caller cannot distinguish from a real answer.

Suggested fix

Remove the blanket handler and let the exception propagate — both call sites already have their own try/except with logger.exception around the create. At minimum, log the failure and re-raise.

Tests

No existing test references _find_existing_bot.

Start in core/switch_core/bridges/collaboration/mattermost/adapter.py at _find_existing_bot and inspect its callers at lines 973 and 1125. Add focused coverage for a lookup exception; done when lookup failures are no longer converted to None and the existing caller error handling can record the real failure.