A follow request sent again carries a new id

Lemmy keeps the ids of the activities it received and never answers one again, so resending the same Follow could not
heal a follow whose Accept it lost: the village's community follow stayed pending through two resends. Each resend is
now the same follow under its own id (<follow id>-again-<n>), and an Accept naming any of them answers the follow;
the Undo still embeds the follow, so servers match it by its actor and object. Sent this way, the stuck follow was
accepted at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

docs/INTEROP.md

@@ -533,6 +533,9 @@ What it showed:
 - **Every bare `Announce{object}` is answered 400** (`Failed to parse object`: Lemmy dereferences it expecting an
   activity), as Lemmy answers the compatibility `Announce(Page)` it sends itself. Both 400s show up as dead deliveries
   in the statistics.
+- **It keeps the ids of the activities it received and never answers one again.** A follow it took and whose Accept it
+  lost (sent before its worker for our server started) stayed pending through two resends of the same Follow; sent
+  under a new id (2026-10-05), it was accepted at once (the village's community follow, pending since 05:06).
 - **Votes travel only to the community**, which relays them as `Announce{Like}` and `Announce{Dislike}`: counted since
   ed08f80, and a vote turned the other way replaces the first since bbeeda7. A moderator's removal, lock and ban come
   the same way and are applied since 2026-10-05 (the removal was applied all along; the scenario gave up before Lemmy's