Unreleased: host_busy on GET /backup/status (R-921), a missing tunnel container is 'absent' and not-applicable after an OS update (R-1070), the janitor forces a half-removed vzdump snapshot once (R-1010)

internal/localapi/server.go

@@ -1343,6 +1343,20 @@ type BackupStatusResponse struct {
 	// presence. Served on the UNTARGETED request only; additive, so an older controller reads the
 	// response exactly as before.
 	Tiers []TierBackupState `json:"tiers,omitempty"`
+	// HostBusy (R-921, agent Unreleased 2026-10-19) says whether the host-wide heavy-operation gate is held RIGHT NOW
+	// (another guest's backup, the restore test, a night OS step, the stale-lock sweep, a power-off) — a POST /backup
+	// would then be refused with 409. The controller reads it BEFORE it stops the household's apps, so a refused tier
+	// costs no stop. Served on every request; ABSENT (nil) = an older agent, or the gate is not wired — the controller
+	// then keeps its old order (stop, ask, resume at once on 409). A read, never a reservation: the gate can be taken
+	// between this answer and the POST, and that race keeps the old order. Pinned by TestBackupStatus_R921_HostBusy.
+	HostBusy *HostBusyState `json:"host_busy,omitempty"`
+}
+
+// HostBusyState is GET /backup/status's host_busy (R-921). What names the holder ("backup:local", "restore-test",
+// "os-pve-step" …), empty when Busy is false.
+type HostBusyState struct {
+	Busy bool   `json:"busy"`
+	What string `json:"what,omitempty"`
 }
 
 func (s *Server) handleBackupStatus(w http.ResponseWriter, r *http.Request, vmid int) {
@@ -1362,6 +1376,10 @@ func (s *Server) handleBackupStatus(w http.ResponseWriter, r *http.Request, vmid
 		resp.JobID = job.JobID
 		resp.Error = job.Error
 	}
+	if s.inFlight != nil {
+		what := s.inFlight.Busy()
+		resp.HostBusy = &HostBusyState{Busy: what != "", What: what}
+	}
 	writeOK(w, resp)
 }