fix(backend): skip inbox activities without an actor instead of throwing TypeError (#17558)

* fix(backend): skip inbox activities without an actor instead of throwing TypeError

- guard getApId() against null/undefined (and fix the 'detemine' typo)
- skip actor-less inbox activities early with Bull.UnrecoverableError

Fixes #17557

* fix(backend): reject actor-less inbox activities at enqueue time

Per review feedback (#17558), move the actor presence check to the inbox
HTTP handler and drop the processor-side guard.

- ActivityPubServerService.inbox(): validate the request body from the
  loose (unknown) type and return 400 for structurally invalid activities
  (non-object / missing actor) instead of enqueueing a job that can never
  be authenticated. Avoids useless retries and TypeError noise.
- InboxProcessorService.process(): remove the actor null guard; IActivity.actor
  is non-null, so the check is unnecessary once enqueue is validated.
- getApId(): widen the parameter to include undefined so the existing null
  guard is type-honest (getOneApId can pass value[0] of an empty array).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/backend/src/server/ActivityPubServerService.ts

@@ -174,7 +174,17 @@ export class ActivityPubServerService {
 			}
 		}
 
-		this.queueService.inbox(request.body as IActivity, signature);
+		const body = request.body;
+
+		// Reject structurally invalid activities (e.g. missing actor) here instead
+		// of letting them fail deep inside the inbox processor. An actor-less
+		// activity can never be authenticated, so there is no point enqueueing it.
+		if (typeof body !== 'object' || body == null || !('actor' in body) || body.actor == null) {
+			reply.code(400);
+			return;
+		}
+
+		this.queueService.inbox(body as IActivity, signature);
 
 		reply.code(202);
 	}