Finding 1: handleReactionAdd/Remove now drop reactions on a dead 1-on-1
(isDeadOneOnOne) — previously a survivor could react on a Deleted-User
thread and the relay fanned out to all peers via undefined target-origins.
Client Message.tsx withdraws add/toggle reaction affordances for dead DMs
(existing reactions still display read-only).
Finding 2: dmMembership purge test now runs with foreign_keys=ON (matches
prod) and asserts dm_members/dm_messages cascade cleanup on channel purge.
Finding 3: tombstone group-DM ownership transfer filters isDeleted=0 so
ownership can never move to a tombstoned member; covered by a new test.
Jannis Braun