Discord threads where the bot has already participated bypass mention gating by default, but the backfill check was still tied to the mention-needed condition. That meant follow-up thread messages could trigger a response without providing recent thread history to the session.
Run history backfill for thread messages whenever backfill is enabled, while keeping DMs skipped and channel mention backfill behavior unchanged. Add a regression test for a known thread follow-up without an explicit mention.
Fixes#33666
Co-authored-by: Cursor <cursoragent@cursor.com>
eafe11d456