With `require_mention: true` + `bots_require_mention: true` + wake words in `mention_patterns`, a message
authored by another Hermes bot that addressed this bot by name matched no dispatch path (the
bot-to-bot loop breaker skips it) and was also refused by the observe gate (`mention_patterns`
matches are assumed dispatched), so it vanished from both paths with no log line.
Factor the loop-breaker predicate into `_bot_sender_suppressed` and consult it in
`_should_observe_unmentioned_group_message`, so every message the dispatcher drops because of
`bots_require_mention` is kept as observed context instead of being lost (#115119).
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