fix: resolve memory leak in useReconnectCountdown hook

[Makeepan-dev]

Proposed changes

This PR resolves a memory leak in apps/meteor/client/components/connectionStatus/useReconnectCountdown.ts.

The Issue:

The setInterval used to manage the reconnect countdown timer was not being properly cleared when the component unmounted. Because the interval ID was stored in a useRef (reconnectionTimerRef.current), if the component unmounted while the status was 'waiting', the timer would continue running orphaned in the background.

The Fix:

• Added a proper return cleanup function to the useEffect hook.
• Cleared the interval explicitly using reconnectionTimerRef.current.
• Defensively reset the ref to undefined to ensure a clean state initialization on subsequent renders.

Issue(s)

Found via static analysis auditing for unhandled subscription/listener cleanups. (No existing issue number).

Steps to test or reproduce

1. Force the Rocket.Chat client into a disconnected/reconnecting state so the useReconnectCountdown component mounts and status becomes 'waiting'.
2. Trigger an unmount of the component while the countdown is actively running.
3. Observe via React DevTools or memory profiling that the interval no longer continues executing in the background.

Further comments

The fix defensively checks for the existence of reconnectionTimerRef.current before calling clearInterval and resets the reference, ensuring no stale closures or ghost intervals persist.

Task: ARCH-1978

[dionisio-bot]

Looks like this PR is not ready to merge, because of the following issues:

• This PR is missing the 'stat: QA assured' label

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[CLAassistant]

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[changeset-bot]

⚠️ No Changeset found

Latest commit: cd1dd0f

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[cubic-dev-ai]

No issues found across 1 file

[ggazzo]

/jira ARCH-1935