Improve Realtime Frontend

Operation

Implement the requested coherent change at the owning source and update directly affected consumers. An earlier audit is optional when the user and repository already establish the target. Validate the changed behavior, then stop when the requested scope is complete.

Goal

Implement one selected, evidence-backed Realtime Frontend improvement at the authoritative owner. Complete the directly affected contract without broad cleanup or redesign.

Domain rules

• Centralize query-key and entity/version rules and change every affected query, mutation, prefetch, subscription, and persistence path together.
• When the repository uses TanStack Query, use its cancellation, invalidation, mutation, structural-sharing and persistence boundaries. Otherwise use equivalent capabilities of the existing state library; do not introduce a new library merely to follow this recipe.
• Make optimistic operations concurrency-safe with operation-scoped snapshots/context and authoritative response/event reconciliation.
• Reconnect by proving continuity through sequence/resume token or fetching a fresh snapshot; bound backoff, buffers, and refetch fan-out.
• Optimize only measured dominant render/cache/network work and preserve correctness under errors, offline, hidden tabs, and unmount.

Validation

• Run component/integration tests with deterministic query client, network/event fixtures, fake time where appropriate, and real browser profiling for performance claims.
• Exercise overlapping mutations, rollback, duplicate/out-of-order/gap events, reconnect/focus/offline, persisted-cache user switch, unmount, and slow consumer behavior.
• Compare before/after request count, cache transitions, commit duration/count, long tasks, memory, event lag, and recovery.