Extract a PresencePort seam (async setFocus/clearSocket/isViewing) with two
impls: the existing in-memory Map (dev, single instance) and a new
RedisPresenceService (prod). MessageModule provides PRESENCE_PORT via a
REDIS_URL-gated factory — same pattern as the socket.io Redis adapter — so
'who is viewing what' is shared across replicas and the notification projector's
presence gate works at N>1. Gateway + projector inject the port; isViewing is
now awaited. Presence spec updated to async (passing).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
maaz519
1cbfddd4c2