[Web] GraphQL subscription leaks — NotificationStore, ApplicationSettings, Matchmaking, MatchLobby

[Flegma]

Summary

Multiple Pinia stores create GraphQL subscriptions that are never unsubscribed, causing memory leaks that grow over the session lifetime.

Findings

• NotificationStore — three subscriptions in subscribeToAll() never stored for cleanup. Called multiple times on auth changes.
• ApplicationSettings — setInterval created inside subscription callback. New interval on every settings update without clearing old ones.
• MatchmakingStore — subscribeToFriends, subscribeToMatchInvites, subscribeToLobbies called on auth changes via watch, old subscriptions never cleaned up.
• MatchLobbyStore — all subscription methods called from AuthStore but never returned or stored for cleanup.

Impact

Memory and connection usage grows with each auth state change. Long sessions accumulate hundreds of active subscriptions.

Suggested Fix

Create a useSubscriptionManager() composable that stores subscription references, auto-unsubscribes previous on same key, and provides cleanup on logout/unmount.

---

Related Issues (Memory Leak Pattern)

• [API] Missing NestJS lifecycle cleanup — intervals, recursive timeouts, stale WS refs #375 — [API] Missing NestJS lifecycle cleanup
• [Web] GraphQL subscription leaks — NotificationStore, ApplicationSettings, Matchmaking, MatchLobby #385 — [Web] GraphQL subscription leaks
• [Web] Socket listeners & component event handlers never cleaned up #386 — [Web] Socket listeners never cleaned up
• [Game Server] Resource disposal — HttpClient, WebSocket, Timer, pending messages accumulation #398 — [Game Server] Resource disposal issues
• [Connector] Network monitoring process leak & throttle instance accumulation #407 — [Connector] Network process leak & throttle accumulation