Two correctness bugs in the real-time stack — both silent failures, both
session-wide once they trigger.
(1) `SocketProvider` was setting the React context to null on every
`disconnect` event. socket.io's built-in reconnection re-establishes the
underlying transport and replays handlers, but the React tree had
already lost its reference to the socket — so every `useSocket()`
consumer saw null until a session/port change forced a remount. Effect:
after the first transient drop (laptop sleep, wifi blip, server
restart), realtime invalidation and toasts went dead session-wide with
no user-visible signal.
Fix: keep the socket reference stable for the lifetime of the
session+port, and surface a separate `isConnected` boolean for any UI
that wants to render an offline indicator. Exposed as a new
`useIsSocketConnected()` hook; `useSocket()` signature is unchanged.
(2) `useRealtimeInvalidation` captured `eventMap` as a useEffect
dependency. Every caller passes a fresh `{ ... }` object literal on each
render, so the effect re-ran every render → `socket.off`/`socket.on`
storm on pages with many subscribed events.
Fix: extract the subscription logic into a pure helper
(`realtime-invalidation-core.ts`, JSX-free for vitest). The hook now
keeps the latest map in a ref and only re-subscribes when the SET of
event names changes (joined-keys signature, not object identity). The
handler reads `ref.current` at fire time, so callers still see fresh
queryKey lists without re-binding.
Helper is unit-tested with a stub socket: registration count,
fire-time map lookup, cleanup deregistration, missing-event safety.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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