Live migrate VM failed when 'Error-ed" VM snapshots exists and VM stopped.

### problem

Live migrate VM failed when 'Error-ed" VM snapshots exists and VM stopped.

```
2026-04-10 08:06:55,931 DEBUG [c.c.a.m.ClusteredAgentAttache] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026430: Routed from 32986137363417
2026-04-10 08:06:55,933 DEBUG [c.c.a.t.Request] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026430: Sending { Cmd , MgmtId: 32986137363417, via: 1(ref-trl-11538-k-Mol8-suresh-anaparti-kvm1), Ver: v1, Flags: 100011, [{"com.cloud.agent.api.RestoreVMSnapshotCommand":{"snapshots":[{"id":"1","snapshotName":"i-2-3-VM_VS_20260410080110","type":"DiskAndMemory","createTime":"1775808070000","quiescevm":"true"}],"snapshotAndParents":{},"volumeTOs":[{"uuid":"4fbf60a0-9ecb-4fa5-8238-35363309b8fe","volumeType":"ROOT","dataStore":{"org.apache.cloudstack.storage.to.PrimaryDataStoreTO":{"uuid":"d90d639c-b4df-387d-a3cc-c4a9fad1a939","name":"ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2","id":"2","poolType":"NetworkFilesystem","host":"10.0.32.4","path":"/acs/primary/ref-trl-11538-k-Mol8-suresh-anaparti/ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2","port":"2049","url":"NetworkFilesystem://10.0.32.4/acs/primary/ref-trl-11538-k-Mol8-suresh-anaparti/ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2/?ROLE=Primary&STOREUUID=d90d639c-b4df-387d-a3cc-c4a9fad1a939","isManaged":"false"}},"name":"ROOT-3","size":"(8.00 GB) 8589934592","path":"4fbf60a0-9ecb-4fa5-8238-35363309b8fe","volumeId":"3","vmName":"i-2-3-VM","accountId":"2","format":"QCOW2","provisioningType":"THIN","poolId":"2","id":"3","deviceId":"0","hypervisorType":"KVM","directDownload":"false","deployAsIs":"false","followRedirects":"false"},{"uuid":"f98a16a9-d53a-4c32-b1c4-f20340435757","volumeType":"DATADISK","dataStore":{"org.apache.cloudstack.storage.to.PrimaryDataStoreTO":{"uuid":"c3812f1e-6c98-408b-80bf-8c294ecef883","name":"pflexcspool1","id":"5","poolType":"PowerFlex","host":"10.0.32.170","path":"3357f56800000000","port":"0","url":"PowerFlex://10.0.32.170/3357f56800000000/?ROLE=Primary&STOREUUID=c3812f1e-6c98-408b-80bf-8c294ecef883","isManaged":"true"}},"name":"MyDATA01","size":"(8.00 GB) 8589934592","path":"8a4d19710000005a:vol-20-2f1e-7565","volumeId":"20","vmName":"i-2-3-VM","accountId":"2","format":"QCOW2","provisioningType":"THIN","poolId":"5","id":"20","deviceId":"1","hypervisorType":"KVM","directDownload":"false","deployAsIs":"false","followRedirects":"false"}],"vmName":"i-2-3-VM","guestOSType":"CentOS 5.5 (64-bit)","wait":"0","bypassHostMaintenance":"false"}}] }
2026-04-10 08:06:55,950 DEBUG [c.c.a.t.Request] (AgentManager-Handler-14:[]) (logid:) Seq 1-5825124643027026430: Processing: { Ans: , MgmtId: 32986137363417, via: 1, Ver: v1, Flags: 10, [{"com.cloud.agent.api.Answer":{"result":"false","details":"java.lang.NullPointerException: Cannot invoke "java.lang.Boolean.booleanValue()" because the return value of "com.cloud.agent.api.VMSnapshotTO.getCurrent()" is null
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRestoreVMSnapshotCommandWrapper.execute(LibvirtRestoreVMSnapshotCommandWrapper.java:69)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRestoreVMSnapshotCommandWrapper.execute(LibvirtRestoreVMSnapshotCommandWrapper.java:39)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRequestWrapper.execute(LibvirtRequestWrapper.java:78)
at com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.executeRequest(LibvirtComputingResource.java:1973)
at com.cloud.agent.Agent.processRequest(Agent.java:778)
at com.cloud.agent.Agent$AgentRequestHandler.doTask(Agent.java:1193)
at com.cloud.utils.nio.Task.call(Task.java:83)
at com.cloud.utils.nio.Task.call(Task.java:29)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)
","wait":"0","bypassHostMaintenance":"false"}}] }
...
2026-04-10 08:06:55,951 INFO [c.c.v.ClusteredVirtualMachineManagerImpl] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Migration was unsuccessful. Cleaning up: VM instance {"id":3,"instanceName":"i-2-3-VM","state":"Running","type":"User","uuid":"7b213c30-2290-4801-beb9-5a70a3b5ce3d"}

2026-04-10 08:06:59,232 DEBUG [c.c.a.t.Request] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026433: Sending { Cmd , MgmtId: 32986137363417, via: 1(ref-trl-11538-k-Mol8-suresh-anaparti-kvm1), Ver: v1, Flags: 100011, [{"com.cloud.agent.api.StopCommand":{"isProxy":"false","checkBeforeCleanup":"false","forceStop":"false","vlanToPersistenceMap":{"2671":"true"},"volumesToDisconnect":[],"vmName":"i-2-3-VM","executeInSequence":"false","wait":"0","bypassHostMaintenance":"false"}}] }
2026-04-10 08:06:59,232 WARN [c.c.v.ClusteredVirtualMachineManagerImpl] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Unable to transition to a new state from Running via OperationFailed

2026-04-10 08:06:59,235 INFO [c.c.v.VmWorkJobHandlerProxy] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Rethrow exception java.lang.ClassCastException: class com.cloud.agent.api.Answer cannot be cast to class com.cloud.agent.api.RestoreVMSnapshotAnswer (com.cloud.agent.api.Answer and com.cloud.agent.api.RestoreVMSnapshotAnswer are in unnamed module of loader 'app')
2026-04-10 08:06:59,235 DEBUG [c.c.v.VmWorkJobDispatcher] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118]) (logid:bfef3797) Done with run of VM work job: com.cloud.vm.VmWorkMigrate for VM 3, job origin: 117
2026-04-10 08:06:59,236 ERROR [c.c.v.VmWorkJobDispatcher] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118]) (logid:bfef3797) Unable to complete AsyncJob {"accountId":2,"cmd":"com.cloud.vm.VmWorkMigrate","cmdInfo":"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-AAlwcQB-AAk","cmdVersion":0,"completeMsid":null,"created":"Fri Apr 10 08:06:34 UTC 2026","id":118,"initMsid":32986137363417,"instanceId":null,"instanceType":null,"lastPolled":null,"lastUpdated":null,"processStatus":0,"removed":null,"result":null,"resultCode":0,"status":"IN_PROGRESS","userId":2,"uuid":"76ff9b90-ac44-4ed9-89d9-43a3a777b16f"}, job origin: 117 java.lang.ClassCastException: class com.cloud.agent.api.Answer cannot be cast to class com.cloud.agent.api.RestoreVMSnapshotAnswer (com.cloud.agent.api.Answer and com.cloud.agent.api.RestoreVMSnapshotAnswer are in unnamed module of loader 'app')
at com.cloud.vm.VirtualMachineManagerImpl.checkVmOnHost(VirtualMachineManagerImpl.java:2405)
at com.cloud.vm.VirtualMachineManagerImpl.migrate(VirtualMachineManagerImpl.java:2875)
at com.cloud.vm.VirtualMachineManagerImpl.orchestrateMigrate(VirtualMachineManagerImpl.java:2733)
at com.cloud.vm.VirtualMachineManagerImpl.orchestrateMigrate(VirtualMachineManagerImpl.java:5524)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:569)
at com.cloud.vm.VmWorkJobHandlerProxy.handleVmWorkJob(VmWorkJobHandlerProxy.java:102)
at com.cloud.vm.VirtualMachineManagerImpl.handleVmWorkJob(VirtualMachineManagerImpl.java:5621)
at com.cloud.vm.VmWorkJobDispatcher.runJob(VmWorkJobDispatcher.java:99)
at org.apache.cloudstack.framework.jobs.impl.AsyncJobManagerImpl$5.runInContext(AsyncJobManagerImpl.java:661)
at org.apache.cloudstack.managed.context.ManagedContextRunnable$1.run(ManagedContextRunnable.java:49)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext$1.call(DefaultManagedContext.java:56)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext.callWithContext(DefaultManagedContext.java:103)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext.runWithContext(DefaultManagedContext.java:53)
at org.apache.cloudstack.managed.context.ManagedContextRunnable.run(ManagedContextRunnable.java:46)
at org.apache.cloudstack.framework.jobs.impl.AsyncJobManagerImpl$5.run(AsyncJobManagerImpl.java:609)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)
```

### versions

ACS 4.20.3 RC4 + Advanced Zone + KVM hypervisor

### The steps to reproduce the bug

1. Deploy a VM
2. Create VM snapshot (should fail, otherwise update state to Error in DB)
3. Live migrate VM to another host

### What to do about it?

Expecting Live migrate VM to succeed (even when failed/error-ed VM snapshots exists), and VM shouldn't be stopped in case of migration failure.

Bắt đầu với LibvirtRestoreVMSnapshotCommandWrapper.java tại dòng được báo cáo nơi VMSnapshotTO.getCurrent() được sử dụng, sau đó truy vết VirtualMachineManagerImpl.checkVmOnHost() và luồng dọn dẹp migration. Tái hiện trường hợp snapshot VM bị failed hoặc ở trạng thái Error và xác minh rằng live migration thành công mà không dừng VM khi migration thất bại.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.