fix(envd): replace time.Sleep with ticker in ScanAndBroadcast for prompt shutdown

[AdaAibaby]

fixes #3356

Problem

ScanAndBroadcast() used time.Sleep inside a default select case:

select {
case <-s.scanExit:
    return
default:
    time.Sleep(s.period)  // ← Destroy() is invisible here
}

Destroy() closes scanExit, but the goroutine only checks scanExit at the top of each iteration — before the sleep starts. Once time.Sleep is entered, a concurrent Destroy() call is not noticed until the sleep completes. With portScannerInterval = 1 s, every envd shutdown was delayed by up to 1 second waiting for the port scanner goroutine.

Fix

Replace time.Sleep with time.NewTicker so scanExit and the tick interval are waited on simultaneously in a single select:

func (s *Scanner) ScanAndBroadcast() {
    ticker := time.NewTicker(s.period)
    defer ticker.Stop()

    for {
        processes, _ := net.Connections("tcp")
        for _, sub := range s.subs.Items() {
            sub.Signal(processes)
        }
        select {
        case <-s.scanExit:
            return          // exits immediately on Destroy()
        case <-ticker.C:
        }
    }
}

Destroy() now unblocks the goroutine instantly, regardless of how far into the current interval it is.

Using a Ticker (instead of time.After) also avoids allocating a new timer object on every loop iteration.

Tests

Two new tests in scan_test.go:

• TestScanAndBroadcastDestroyExitsPromptly — creates a scanner with a 5 s period, lets it enter the select block, calls Destroy(), and asserts the goroutine exits within 200 ms (not after 5 s).
• TestScanAndBroadcastDestroyBeforeSleep — calls Destroy() before ScanAndBroadcast starts, verifying the goroutine still exits promptly.

Both pass in < 100 ms total.

/cc @jakubno @dobrac @ValentaTomas

[arkamar]

Thanks for the change, LGTM. I think the tests are not needed for this, as they could easily become flaky, at least as they were written. The timing assertions could false-fail on a loaded runner. The fix itself is a straightforward select on scanExit, verifiable by inspection.

I removed the additional comment from ScanAndBroadcast() as it described the implementation detail rather than the contract, and the original one-liner still covers what the function does.

I pushed these changes directly to your branch, along with the envd version bump to 0.6.11. The remaining diff is just the sleep→ticker change, which is exactly what we want here.