Faol's replies can't duplicate anymore

A heartbeat turn re-replied to three Bluesky posts Faol had already answered, including two from the day before. The prompt told him to only reply to notifications newer than a state timestamp, but a 20B model doesn't reliably do ISO-date filtering mid-turn. Instructions weren't enough.

What changed

• reply in the faol-atproto harness is now idempotent: if the target URI is in .replied-uris, it prints ALREADY REPLIED ... skipping and posts nothing. Successful replies append their target.
• .replied-uris backfilled from his author feed (21 posts).
• The heartbeat prompt no longer checks mentions at all — the reactive watcher owns them, mechanically, via its own state file and lock.
• The three duplicate replies were deleted.

Checked

• Refusal path: replying to an already-answered URI skips without a network call.
• Author feed shows only the original replies.