feat: fix panic on empty Events array in etcd watch response

[Copilot]

etcd watch responses can contain progress notifications or empty event arrays, causing res.Events[0] to panic with index out of bounds.

Changes

• Added check for IsProgressNotify() to skip health check/keep-alive messages
• Added length check before accessing res.Events[0] to handle empty arrays

func (w *Watcher) startWatch() error {
    watcher := w.client.Watch(context.Background(), w.keyName)
    for res := range watcher {
        // Skip progress notifications
        if res.IsProgressNotify() {
            continue
        }
        // Skip empty events
        if len(res.Events) == 0 {
            continue
        }
        t := res.Events[0]
        // ... rest of event processing
    }
}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• go.etcd.io
  • Triggering command: /update-job-proxy /update-job-proxy -c=4 (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy DROP ache/go/1.24.11/--global test -e ntrust_Root_Certgit@github.com/ ache/go/1.24.11//usr/share/ca-certificates/mozilla/SecureTrust_CA.crt (dns block)
• go.googlesource.com
  • Triggering command: /update-job-proxy /update-job-proxy -c=4 (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy DROP ache/go/1.24.11/--global test -e ntrust_Root_Certgit@github.com/ ache/go/1.24.11//usr/share/ca-certificates/mozilla/SecureTrust_CA.crt (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>etcd watcher events maybe empty</issue_title>
<issue_description>etcd watcher RequestProgress maybe send message empty event; t := res.Events[0] will panic

func (w *Watcher) startWatch() error {
	watcher := w.client.Watch(context.Background(), w.keyName)
	for res := range watcher {
                // to check ProgressNotify
		if res.IsProgressNotify() {
			continue
		}
		t := res.Events[0]
		if t.IsCreate() || t.IsModify() {
			w.lock.RLock()
			//ignore self update
			if rev := t.Kv.ModRevision; rev > w.lastSentRev && w.callback != nil {
				w.callback(strconv.FormatInt(rev, 10))
			}
			w.lock.RUnlock()
		}
	}
	return nil
}</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes etcd watcher events maybe empty #26

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[coveralls]

coverage: 80.808% (-3.2%) from 84.043%
when pulling bec95a9 on copilot/fix-etcd-watcher-empty-events
into 2f2c69e on master.