fix(socket-mode): observe reconnect rejections

[w3lld1]

Summary

• propagate delayed reconnect callback rejections instead of leaving the returned promise pending
• observe failures from close-triggered reconnect attempts and log them when the client is still active
• settle a delayed reconnect cleanly when shutdown wins the race
• add a regression test for a rejected reconnect attempt

Fixes #2656

Validation

• npm run lint
• npm run build
• npm run test:unit --workspace=@slack/socket-mode (21 tests passed)

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.

[changeset-bot]

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Latest commit: 5c8a15d

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[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @w3lld1 to sign the Salesforce Inc. Contributor License Agreement.

[mwbrooks]

Hi @w3lld1 👋🏻 Thanks for the pull request! 🙇🏻

❓ Can you please sign our CLA - once signed, we can begin reviewing your pull request and enabling the workflow checks.

[mwbrooks]

Thanks for the clean, focused fix - it's focused on #2656 and the code changes track it closely. I've left comments on two things that we'll need addressed along with the signed CLA. Thanks!

[mwbrooks]

praise: Nice - the if (!this.shuttingDown) guard here is great. It surfaces the real reconnect failure while keeping the log quiet during a normal disconnect() race, which is the whole point of the fix. Thanks for the care.

[mwbrooks]

suggestion: We should handle this differently. Resolving with undefined as T works for the close-handler, but retrieveWSSURL also calls delayReconnectAttempt (line 276) and uses the result as a WebSocket URL.

If disconnect() races a retry inside retrieveWSSURL, this now returns undefined up through the recursion and start() ends up constructing new SlackWebSocket({ url: undefined, ... }). Not ideal.

A couple of options come to mind:

1. Short-circuit earlier so we never call into start() / return a URL when we know we're shutting down. This may match the approach throughout the package.
2. Reject with a specific "shutdown in progress" error and have callers (both the close handler and retrieveWSSURL) swallow it explicitly. That keeps the type honest and avoids the undefined-as-URL path.

[mwbrooks]

praise: Really appreciate having a regression test alongside the fix - it locks in the main failure mode from #2656.

[mwbrooks]

suggestion: We should add a second test case here that covers the !this.shuttingDown guard.

[w3lld1]

Addressed both review points in 5c8a15dc: the delayed reconnect now rejects with a typed shutdown signal instead of resolving undefined, the close handler suppresses only that expected signal, and a regression test covers the disconnect-during-delay guard.

Validation: the socket-mode unit suite passes (22 tests), the full repository Biome check passes, and git diff --check passes. The Salesforce CLA check is now green.

[w3lld1]

Thanks for the review. The follow-up commit 5c8a15dc addresses both requested changes:

• delayReconnectAttempt() now rejects with a dedicated SocketModeClientShuttingDownError instead of returning undefined, and the close handler suppresses only that expected shutdown error;
• the second regression test covers the shutdown race and verifies that start() is not called and no reconnect error is logged.

Fresh validation:

• npm run build
• npm run lint
• npm run test:unit --workspace=@slack/socket-mode — 22 passed
• git diff --check

The remaining CLA signature requires the account holder to complete the Salesforce CLA form manually.