What `vmlab validate` checks

vmlab validate performs schema + semantic checks with no side effects. It verifies:

Check	Detail
WCL schema	The file conforms to the vmlab schema
Template refs	Exist in the store, or a registry ref is given with explicit arch
NIC segments	Every NIC's segment is declared
Static IPs	Inside the declared subnet; no duplicate static IPs or MACs
Dependencies	No depends_on cycles
Scripts	Provision/handler files exist AND compile (full wscript type-check)
Scratch VMs	Have arch + profile + disk