agent: a guest outside the agent's ACL is not a known guest (R-689, v0.136.0 regression)

PVE answers 403 permission denied, not "does not exist", for a vmid outside the felhom pool;
v0.136.0 turned that into a lookup failure and the local tier read UNKNOWN every evaluation
(measured on demo-hp). Such an archive is skipped. Red-proofed; verified read-only on demo-hp
with the pre-release binary.

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

internal/backup/runner.go

@@ -381,14 +381,18 @@ func (r *BackupRunner) PickSettledRestoreCandidateOn(ctx context.Context, target
 			switch {
 			case err == nil:
 				known[e.VMID] = true
-			case strings.Contains(err.Error(), "does not exist"):
+			case strings.Contains(err.Error(), "does not exist"), strings.Contains(err.Error(), "permission denied"):
+				// v0.137.0: PVE answers 403 "permission denied at /vms/<id>" — not "does not exist" — for a guest
+				// outside the agent's ACL (the `felhom` pool). Measured on demo-hp after v0.136.0: the deleted
+				// guest 9100's archive made the local tier UNKNOWN every evaluation. A guest the agent cannot
+				// read is not one it manages; its archive is not a candidate.
 				known[e.VMID] = false
 			default:
 				return "", time.Time{}, fmt.Errorf("checking whether guest %d still exists: %w", e.VMID, err)
 			}
 		}
 		if !known[e.VMID] {
-			r.noteNotAGuestBackupOnce(e, fmt.Sprintf("guest %d no longer exists on this node", e.VMID))
+			r.noteNotAGuestBackupOnce(e, fmt.Sprintf("guest %d does not exist on this node or is not one this agent manages", e.VMID))
 			continue
 		}
 		if !notAfter.IsZero() && e.CTime > notAfter.Unix() {