Funkwhale's answers, deletions and NodeInfo are understood

Three shapes Funkwhale 2.0 sends, each of which lost something:
- its Accept is named after the Follow it answers, on our origin (`…#follows/<uuid>/accept`), and was refused as off its
  actor's origin, so no follow of a channel completed: an Accept or Reject whose id extends the id of the activity it
  answers, on our origin, is now taken;
- a channel deletes its uploads in one Delete without an id, their ids in a list as the object's id: each is deleted;
- its NodeInfo discovery names the document under its swagger schema's URL: a link whose path names NodeInfo is taken
  when no rel is known.

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

PrivaPub/Federation/Inbox/InboxReceiver.cs

@@ -222,7 +222,10 @@ namespace PrivaPub.Federation.Inbox
 		async Task<InboxResult> ShapeProblem(string type, JsonNode activity, string actorUri, CancellationToken token)
 		{
 			var activityId = Id(activity);
-			if (activityId != default && !Origin.Same(activityId, actorUri))
+			// (Funkwhale names its answer after the activity it answers: `<our Follow's id>/accept`)
+			if (activityId != default && !Origin.Same(activityId, actorUri)
+				&& !(type is "Accept" or "Reject" && Id(activity["object"]) is { } answered && Origin.Same(answered, _localActors.BaseAddress)
+					&& activityId.StartsWith(answered + "/", StringComparison.Ordinal)))
 				return new(StatusCodes.Status400BadRequest, "the activity's id is not on its actor's origin", Reason: "id-cross-origin");
 
 			var inner = activity["object"];