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

PrivaPub/Federation/Inbox/Handlers/AnnounceHandler.cs

@@ -198,12 +198,15 @@ namespace PrivaPub.Federation.Inbox.Handlers
 						return;
 					}
 					Arrival.About(visibility: deleted.Visibility, created: deleted.CreationDate);
-					using (var check = await _remoteActors.FetchObject(objectUri, token))
-						if (check != default && Value(System.Text.Json.Nodes.JsonNode.Parse(check.Root.GetRawText()), "type") != "Tombstone")
-						{
-							Arrival.Drop("not-deleted");
-							return;
-						}
+					// a community on the post's own server speaks for it: PieFed keeps serving a thread its moderator removed.
+					// One elsewhere is believed once the post's server says it is gone
+					if (!Origin.Same(objectUri, group.ActorURI))
+						using (var check = await _remoteActors.FetchObject(objectUri, token))
+							if (check != default && Value(System.Text.Json.Nodes.JsonNode.Parse(check.Root.GetRawText()), "type") != "Tombstone")
+							{
+								Arrival.Drop("not-deleted");
+								return;
+							}
 					Arrival.Accept("removed");
 					await RemoteDeletes.Remove(deleted, objectUri, token);
 					break;