Event notifiers used the `mentionees` DB association to exclude mentioned
users from comment/card notifications. Since mentions are created async
via Mention::CreateJob, a race condition meant the mentionee list could
be empty when the event notification job ran first, causing the user to
receive both a comment and a mention push notification.
Use `scan_mentionees` instead, which scans the rich text body directly
for mentioned users without depending on Mention records existing yet.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Rosa Gutierrez
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