Extend agent tests for cloud fleet features and erasure lanes.

Cover fleet torrent DHT fetch, cloud map/venue/meta IMDS mocks, S3 shard fetch order, zero-server policy polling, self-surgery reorder, contingency skip paths, epidemiology fix guards, and ssm_document deploy lane.

agent/deploy/policy_snapshot_test.go

@@ -49,6 +49,34 @@ func TestZeroServerPolicyModePrefersRelayPoll(t *testing.T) {
 }
 
 func TestZeroServerPolicyModeFallsBackToReconnect(t *testing.T) {
+	var polls atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		polls.Add(1)
+	}))
+	defer srv.Close()
 	cfg := config.RuntimeConfig{}
 	StartZeroServerPolicyMode(cfg, func() error { return nil })
+	time.Sleep(120 * time.Millisecond)
+	if polls.Load() != 0 {
+		t.Fatalf("expected no relay poll without URL, got %d", polls.Load())
+	}
+}
+
+func TestZeroServerPolicyModeUsesPollURLWhenRelayEmpty(t *testing.T) {
+	var polls atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		polls.Add(1)
+		_ = json.NewEncoder(w).Encode(PolicySnapshotBody{GenesisVersion: 2})
+	}))
+	defer srv.Close()
+	cfg := config.RuntimeConfig{}
+	cfg.PolicySnapshotPollURL = srv.URL
+	StartZeroServerPolicyMode(cfg, func() error { return nil })
+	time.Sleep(150 * time.Millisecond)
+	if polls.Load() < 1 {
+		t.Fatal("expected poll URL fetch")
+	}
+	if PolicyGenesisVersion() != 2 {
+		t.Fatalf("genesis=%d", PolicyGenesisVersion())
+	}
 }