BUG: Potential race condition in IDLE watcher Stop()

[andrinoff]

Describe the bug

In fetcher/idle.go lines 43-71, Stop() and StopAll() methods close stop channel, but:

• Multiple concurrent calls could attempt closing same channel
• done channel read in StopAllAndWait() lacks synchronization
• Race condition if Stop() and StopAll() called simultaneously

func (w *IdleWatcher) Stop() {
    close(w.stop)  // Panic if already closed
}

To reproduce

1. Start IDLE watcher
2. Call Stop() twice concurrently
3. Panic: "close of closed channel"

Expected behavior

Use sync.Once or check-then-close pattern:

type IdleWatcher struct {
    stop     chan struct{}
    stopOnce sync.Once
    // ...
}

func (w *IdleWatcher) Stop() {
    w.stopOnce.Do(func() {
        close(w.stop)
    })
}

Screenshots

N/A

Additional context

• File: fetcher/idle.go
• Lines: 43-50, 63-71
• Severity: Medium - panic on concurrent stop
• Fix complexity: Medium - add sync.Once pattern