Since a655117 ("tools: start-vmm: enable Cloud Hypervisor landlock"),
it's not possible to reboot a VM:

~ # ch-remote --api-socket /run/vm/by-id/dLPcEC/vmm reboot
[2025-12-07T13:04:25Z ERROR cloud_hypervisor] Fatal error: HttpApiClient(ServerResponse(InternalServerError, Some("[\"Error from API\",\"The VM could not reboot\",\"Error creating console devices\",\"Error creating console device\",\"Permission denied (os error 13)\"]")))
Error: ch-remote exited with the following chain of errors:
  0: http client error
  1: Server responded with InternalServerError
  2: Error from API
  3: The VM could not reboot
  4: Error creating console devices
  5: Error creating console device
  6: Permission denied (os error 13)

I've opened an upstream bug reported about this:

https://github.com/cloud-hypervisor/cloud-hypervisor/issues/7547