Pasture: scenarios run again on the same pasture, and Mastodon's threads

GoToSocial's and Mastodon's scenarios passed once on a fresh pasture only:
their locked follows ended followed, so a second run found no request to
reject, and Mastodon's ended with mastouser blocking alice_masto, so every
follow after it was rejected. Each now unfollows first, and Mastodon's
undoes its block (checking that its Undo{Block} reaches our blocked_by) and
its lock; a run cut short is undone at the start.

Mastodon's scenario also checks the thread backfill live: a reply by an
account nobody here follows is never delivered, and joins the thread once
alice_masto opens it, read from Mastodon's FEP-7888 context.

interop.sh keeps the results of the peers it does not run, so the report
merges a partial rerun. All seven scenarios: 276 pass, 0 fail, 1 expected
(Lemmy moderation, P7).

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

CLAUDE.md

@@ -470,7 +470,8 @@ tools/pasture/run.sh down                                            # removes e
   deliveries are checked through `/api/v1/accounts/:id/statuses` of the sender as Mastodon knows them, or
   `Status.exists?` through `rails runner`. Its actors are numbered (`/ap/users/<id>`), so look URIs up rather than
   build them. Circle posts and a followers-only post survive its signed refetch (`ActivityPub::FetchRemoteStatusService`
-  through `rails runner`). Its block of a persona is checked through our `blocked_by`.
+  through `rails runner`). Its block of a persona, and the unblock that ends the run, are checked through our
+  `blocked_by`; the run starts with that unblock too, since Mastodon rejects every follow from an account it blocks.
 - **Misskey (2026.10.0):** one container on the shared Postgres and Redis. A new Misskey federates with nobody
   (`federation: none`) until `admin/update-meta` says `all`, which `misskey_up` does. Its API is `POST /api/<endpoint>`
   with the token as `i` (`mk` in the scenario); `users/relation` answers a list, `users/notes` leaves replies out unless