PieFed joins the pasture; the instance actor answers at the root

PieFed 1.7.17 (dockurr's image of the release) runs in the pasture with its
Celery worker on the shared Postgres and Redis, and scenarios/piefed.sh
checks it both ways: 29 checks, communities, titled threads, comments, votes
up and down, a community poll and a vote in it, private messages, a
moderator's lock, unlock and removal, the unfollow and statistics.

What it showed:
- PieFed sends a community's announces to the inbox of the Application at a
  peer's root (as Lemmy serves its site actor) and to /inbox otherwise.
  PrivaPub answered 404 at its root, so every announce went to an /inbox it
  does not have. The instance actor now answers at / for ActivityPub
  requests, unsigned under SecureMode as at its own address.
- PieFed keeps serving a thread its moderator removed, so the removal could
  never be checked against the post's origin. A community on the post's own
  server now speaks for it; one elsewhere still waits for the origin to say
  the post is gone.

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

docs/ROADMAP.md

@@ -69,6 +69,9 @@ Written 2026-10-01 from the original 2023 code, the decePubClient UI, a federati
     Funkwhale serve it; Funkwhale's answers named after our follow and its deletions of several uploads.
   - GoToSocial's interaction policies both ways; personas join and leave remote events; third-party replies to a
     persona's posts passed on to its followers (owner decisions 2026-10-05).
+  - wave 2, under way: PieFed in the pasture with a scenario (2026-10-05). What it showed and was fixed: the instance
+    actor answers at the server's root, where PieFed looks for the inbox it announces to; a community's removal of a
+    post on its own server is believed at once.
 - [ ] P7 Threads, communities, moderation, the social graph
 - [ ] P8 Signatures, discovery, the long tail
 - [x] P9 Reading at volume (owner decision 2026-10-04, back from "Cut"): lists, server-side filters, scheduled posts,