Treat connection recovery as a state-convergence problem. The client needs to know its last confirmed version, obtain missed state or a fresh snapshot, apply events idempotently, and expose a recoverable error when the available history cannot bridge the gap.
Define what survives a disconnection
Separate ephemeral signals from durable product state. Presence and typing indicators may expire without replay, while a completed job, message, approval, or notification record usually needs a durable source that a returning client can fetch. For each event family, state whether documented behavior provides a snapshot, a bounded replay window, or only best-effort delivery while connected.
Store a sequence, version, or cursor that lets the client describe its last confirmed state. On reconnect, the server can replay events after that cursor or return a fresh authoritative snapshot. If history has expired, the client should discard unsafe incremental assumptions and reconcile from the snapshot. The interface should not claim current state until this recovery step completes.
Test duplicates, order changes, and unrecoverable gaps
Reconnect can repeat an event that arrived before the connection dropped. Apply events idempotently using stable identifiers or versions. If the transport can deliver across multiple channels or regions, test its documented ordering scope and reject stale versions at the reducer. Arrival time alone is weak evidence when clocks and networks differ.
The matrix should include a disconnect before publish, during publish, after broker acknowledgement, and after client receipt but before local persistence. It should also cover expired recovery history, revoked permission, multiple tabs, and an old client schema. Every case needs an expected durable state, expected visible state, and log evidence explaining how convergence occurred.
Where the service stops
Reality Contact, LLC repairs the bounded application delivery path, but does not warrant a third-party provider, guarantee uninterrupted delivery, certify security or compliance, or work on emergency, medical, life-safety, or other consequential alerting systems. The buyer approves the authoritative event and expected interface states, controls provider accounts and production release, reviews limitations, and decides whether to deploy or extend the repaired path. This is application reliability engineering; it does not replace legal, security, compliance, safety, medical, or professional advice. The service does not work on emergency or life-safety alerts and does not guarantee uninterrupted delivery or a third-party provider's availability.
Sources: Socket.IO connection state recovery; Ably message ordering documentation.