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_capability_test.go

@@ -105,3 +105,28 @@ func TestHostCapabilityChecker_OldAgentNoCaps(t *testing.T) {
 		t.Fatalf("old agent (no caps) state = %s, want ok", cc.GetState("h1"))
 	}
 }
+
+// F2 RED-PROOF: a host already DEGRADED at hub (re)start is left UNSEEDED by the constructor and the
+// FIRST Check emits once — so a box that was already broken when the hub restarted alerts (vs the
+// pre-fix path which seeded it silently and never alerted). Companion: pre-fix the constructor seeded
+// "degraded" and Check saw oldState==newState → no event.
+func TestHostCapabilityChecker_F2_BornDegradedAlerts(t *testing.T) {
+	st := newCapStore(t)
+	st.SaveHostReport("h1", "c1", reportWith(capCritDegraded), store.HostReportDenorm{})
+	var events []string
+	cc := NewHostCapabilityChecker(st, func(_, et, _, _, _, _ string) { events = append(events, et) }, log.New(io.Discard, "", 0))
+	if len(events) != 0 {
+		t.Fatalf("construction must not emit, got %v", events)
+	}
+	if cc.GetState("h1") != "unknown" {
+		t.Fatalf("born-degraded must be left unseeded, GetState = %s want unknown", cc.GetState("h1"))
+	}
+	cc.Check()
+	if len(events) != 1 || events[0] != "agent_capability_degraded" {
+		t.Fatalf("born-degraded first Check → one agent_capability_degraded, got %v", events)
+	}
+	cc.Check() // steady degraded → no duplicate
+	if len(events) != 1 {
+		t.Fatalf("steady degraded must not re-emit, got %v", events)
+	}
+}