backport of commit 7a9e3d2 (#24440)

Co-authored-by: Piotr Kazmierczak <[email protected]>

nomad/fsm.go

@@ -33,7 +33,6 @@ const (
 	IndexSnapshot                        SnapshotType = 2
 	EvalSnapshot                         SnapshotType = 3
 	AllocSnapshot                        SnapshotType = 4
-	TimeTableSnapshot                    SnapshotType = 5
 	PeriodicLaunchSnapshot               SnapshotType = 6
 	JobSummarySnapshot                   SnapshotType = 7
 	VaultAccessorSnapshot                SnapshotType = 8
@@ -48,7 +47,6 @@ const (
 	CSIPluginSnapshot                    SnapshotType = 17
 	CSIVolumeSnapshot                    SnapshotType = 18
 	ScalingEventsSnapshot                SnapshotType = 19
-	EventSinkSnapshot                    SnapshotType = 20
 	ServiceRegistrationSnapshot          SnapshotType = 21
 	VariablesSnapshot                    SnapshotType = 22
 	VariablesQuotaSnapshot               SnapshotType = 23
@@ -60,6 +58,14 @@ const (
 	JobSubmissionSnapshot                SnapshotType = 29
 	RootKeySnapshot                      SnapshotType = 30
 
+	// TimeTableSnapshot
+	// Deprecated: Nomad no longer supports TimeTable snapshots since 1.9.2
+	TimeTableSnapshot SnapshotType = 5
+
+	// EventSinkSnapshot
+	// Deprecated: Nomad no longer supports EventSink snapshots since 1.0
+	EventSinkSnapshot SnapshotType = 20
+
 	// Namespace appliers were moved from enterprise and therefore start at 64
 	NamespaceSnapshot SnapshotType = 64
 )
@@ -1796,9 +1802,10 @@ func (n *nomadFSM) restoreImpl(old io.ReadCloser, filter *FSMFilter) error {
 				return err
 			}
 
-		// COMPAT(1.0): Allow 1.0-beta clusterers to gracefully handle
+		// DEPRECATED: EventSinkSnapshot type only available in pre-1.0 Nomad
 		case EventSinkSnapshot:
-			return nil
+			return fmt.Errorf(
+				"EventSinkSnapshot is an unsupported snapshot type since Nomad 1.0. Executing this code path means state corruption!")
 
 		case ServiceRegistrationSnapshot:
 			serviceRegistration := new(structs.ServiceRegistration)