-- `--vm` is the canonical register-VM flag, symmetric with `--jit` and
-- `--run-llvm`: the flag names the engine, not the action. The pre-0.12.1
-- spelling `--run-vm` is kept as a hidden alias for one release and emits
-- a one-shot stderr hint nudging callers to `--vm`. Hard removal of the
-- alias lands in 0.13.0 alongside the tree-walker drop.
--
-- Both forms run the same engine and produce the same stdout; the only
-- observable difference is the deprecation hint on stderr when the alias
-- is used. The example harness asserts stdout only, so both `-- run:`
-- markers below pass identically.
main x:n>n;y=*x 2;+y 1
-- run: main 5
-- out: 11