hub: F2 — alert on host already degraded/stale at (re)start (seed only healthy) v0.21.0

Constructors seed only healthy hosts; an already-degraded/stale host is left unseeded so the first
Check() emits once (cooldown dedups on hub restart). Born-degraded red-proof + staleness test updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pg8ANF97SEeKYSN5Jxw3qJ

hub/internal/monitor/host_staleness_test.go

@@ -42,20 +42,25 @@ func TestHostStalenessChecker(t *testing.T) {
 		events = append(events, eventType)
 	}
 
-	// Seed already-stale (40m) → state stale, but NO event on init.
+	// F2: already-stale (40m) at construction → left UNSEEDED (not seeded "stale"), NO event on init.
 	backdate(t, db, "h1", 40)
 	sc := NewHostStalenessChecker(st, 30*time.Minute, onEvent, log.New(io.Discard, "", 0))
 	if len(events) != 0 {
-		t.Fatalf("seed must not emit events, got %v", events)
+		t.Fatalf("construction must not emit, got %v", events)
 	}
-	if sc.GetState("h1") != "stale" {
-		t.Fatalf("seeded state = %q, want stale", sc.GetState("h1"))
+	if sc.GetState("h1") != "unknown" {
+		t.Fatalf("born-stale must be left unseeded, GetState = %q want unknown", sc.GetState("h1"))
 	}
 
-	// Same age → no transition.
+	// F2: the FIRST Check on a born-stale host emits host_stale once (persistent-down alerting).
 	sc.Check()
-	if len(events) != 0 {
-		t.Fatalf("no transition expected, got %v", events)
+	if len(events) != 1 || last(events) != "host_stale" {
+		t.Fatalf("born-stale first Check → one host_stale, got %v", events)
+	}
+	// Steady stale → no duplicate.
+	sc.Check()
+	if len(events) != 1 {
+		t.Fatalf("steady stale must not re-emit, got %v", events)
 	}
 
 	// Fresh report → host_recovered.