OS updates, guest fast lane (11 §8 step 2): felhom-os-apply wrapper (R1-R13 refusals, repair first, snapshot.debian.org fallback), FELHOM_OSAPPLY sudoers, the OS leg after the primary backup, hub os_update block + os-report, --selftest=os-update

No automatic undo: a customer guest cannot be snapshotted (R-837, measured).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/localapi/afterbackup_test.go

@@ -0,0 +1,63 @@
+package localapi
+
+import (
+	"context"
+	"net/http"
+	"sync"
+	"testing"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/backup"
+)
+
+// The OS leg (agent v0.140.0) runs after a SUCCESSFUL primary backup, and only then; and it runs BEFORE the
+// host-wide heavy-op gate is released, so a restore-test cannot start in the middle of it (`11` C10).
+// Red-proof: drop the `b.Success &&` guard and the failed-backup sub-case fails; move the call after release()
+// and the gate sub-case fails.
+func TestAfterPrimaryBackup(t *testing.T) {
+	run := func(t *testing.T, failErr string) (calls []int, gateHeld bool) {
+		gate := &backup.InFlight{}
+		b := &fakeBackups{failErr: failErr}
+		srv := newTestServerS(t, &fakeGuests{}, b, &fakeStore{}, nil)
+		srv.inFlight = gate
+		var mu sync.Mutex
+		done := make(chan struct{}, 1)
+		srv.SetAfterPrimaryBackup(func(_ context.Context, vmid int) {
+			rel, _, ok := gate.TryAcquire("probe")
+			mu.Lock()
+			calls = append(calls, vmid)
+			gateHeld = !ok
+			mu.Unlock()
+			if ok {
+				rel()
+			}
+			done <- struct{}{}
+		})
+		h := srv.Handler()
+		if do(t, h, "POST", "/backup", "A", "").Code != http.StatusAccepted {
+			t.Fatal("POST /backup not accepted")
+		}
+		select {
+		case <-done:
+		case <-time.After(500 * time.Millisecond):
+		}
+		time.Sleep(20 * time.Millisecond)
+		mu.Lock()
+		defer mu.Unlock()
+		return calls, gateHeld
+	}
+	t.Run("success runs the leg under the gate", func(t *testing.T) {
+		calls, held := run(t, "")
+		if len(calls) != 1 {
+			t.Fatalf("the leg ran %d time(s), want 1", len(calls))
+		}
+		if !held {
+			t.Fatal("the heavy-op gate was free while the leg ran — a restore-test could overlap it")
+		}
+	})
+	t.Run("a failed backup runs nothing", func(t *testing.T) {
+		if calls, _ := run(t, "vzdump exploded"); len(calls) != 0 {
+			t.Fatalf("the leg ran after a FAILED backup: %v", calls)
+		}
+	})
+}