`runtime_kind='microvm'` passes the DB CHECK, is honoured by placement, and now
has an executor — but `POST /api/missions` rejected the value with 400, so the
only interface that creates missions could not produce one. And `backend`, which
selects the per-CLI rootfs, was not in the create payload at all: it existed as a
column and as a parameter to `vm_create`, with nothing able to set it.
microvm needs no target_node_id at create time, unlike local_herdr: placement
resolves a KVM-capable node at launch and fails the launch when there is none, so
an explicit target is a request rather than a requirement.
461 tests pass, clippy clean.
Co-Authored-By: Claude Opus 5 <[email protected]>
