fix(harness): do not hold recovery on layer-1 signature alerts

alerts_ok は第 2 層（signature なし）のアラートだけを見る。第 1 層のシグネチャ
アラートはプラットフォームが復旧を担う情報であり、Grafana の解決が 8 分遅れると
MTTR に乗ってしまうため除外する。

harness/alerts.go

@@ -108,7 +108,9 @@ func (r *AlertRouter) handleWebhook(w http.ResponseWriter, req *http.Request) {
 			"startsAt": al.StartsAt, "fingerprint": al.Fingerprint, "layer": al.Labels["layer"], "signature": sig}
 		r.app.store.Event(bg, runID, sid, "alert", "grafana", payload)
 		handled++
-		r.setFiring(al.Fingerprint, name, al.Status == "firing")
+		// layer-1 signature alerts are informational (the platform owns the recovery); they must not hold the judge
+		// (campaign 3, 2026-10-08: LegacyUnhealthy resolved 8.5 minutes after the container was back, V-K1 MTTR 631 s)
+		r.setFiring(al.Fingerprint, name, al.Status == "firing" && sig == "")
 		if al.Status != "firing" {
 			r.cancelTimer(al.Fingerprint)
 			continue