When a federated user's identity has been tombstoned (isDeleted=1),
findFederatedUser filters them out, causing resolveOrCreateReplicatedUser
to silently create a new stub — a "zombie" resurrection. This guard checks
for a deleted row before creating a stub and returns null instead.
All 11 call sites across federation.ts and dm.ts have been updated with
appropriate null guards: federation relay handlers reject or skip the event
(participant_not_found / accepted no-op), while dm.ts routes convert null
to undefined so the existing 404 path handles it.
Jannis Braun
4da373c970