fix(socket-mode): reconnect immediately on Slack disconnect refresh

[hippi345]

Summary

When Slack sends {"type":"disconnect"} (including refresh_requested), @slack/socket-mode used to close the current WebSocket before opening a replacement and then treat the close as a reconnection failure. That left apps without a connection for several seconds.

This change handles a Slack-requested disconnect in SocketModeClient by opening the next connection immediately and keeping the old socket until the new one receives hello. A successful refresh is not counted as a consecutive failure.

If the replacement never becomes ready, the client does not stay stuck: a close on the new socket before hello, a close on the old socket while the refresh is still pending, or a hello timeout (clientPingTimeout) aborts the in-flight start(), closes leftover sockets, and recovers through delayReconnectAttempt so real failures still back off.

Until the replacement has received hello, acks are written on the old socket even if the new WebSocket is already OPEN. The remaining limitation is acks already in flight at the moment of switchover (when hello arrives and the old socket is closed).

Fixes #2767.

Changes

• On a Slack type: disconnect message with auto-reconnect enabled, call start() right away instead of websocket.disconnect().
• Keep the previous SlackWebSocket until the replacement handshake completes, then close it.
• If the new socket fails before hello, the old socket dies during the refresh, or hello does not arrive in time: clear the refresh flag, emit disconnected so start() settles, close leftover sockets, and schedule delayReconnectAttempt.
• Increment a connection-attempt id when aborting so a late apps.connections.open cannot attach a socket after recovery has already started.
• While refreshInProgress is true and the old socket is still open, send() / acks use the old socket. The client switches to the new socket only after hello. The only remaining limitation is acks in flight at the moment of that switchover.
• disconnect() during a refresh emits disconnected once.
• If auto-reconnect is disabled, still close the current socket immediately (previous behavior).
• Unexpected drops still use the existing delayReconnectAttempt path.

Testing

• Unit test should acknowledge on the old socket while the new socket is OPEN but has not received hello fails on e4958bb (acks followed isActive() / WebSocket OPEN) and passes after this change.
• Also covered: successful overlap refresh, replacement/close recovery, acks while connecting, a single disconnected if disconnect() runs mid-refresh, auto-reconnect disabled.
• npm test --workspace=packages/socket-mode (unit + integration) on Node 22
• npm run lint

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

This change was prepared with AI assistance and reviewed by the author.

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🦋 Changeset detected

Latest commit: 4bd3f96

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@slack/socket-mode	Patch

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