Package mockexe lets a test binary impersonate an agent CLI: call
Main() first in TestMain; in child processes spawned with Env(spec)
it performs the configured behavior and exits. This replaces
sh mock scripts so adapter/daemon tests run on Windows.
Env returns the environment entries that make a child running the
test binary behave per spec. Append to os.Environ() — or set them via
t.Setenv so children inherit them implicitly.
Spec describes the mocked CLI's behavior. In Stdout/Stderr the token
{LAST} is replaced with the process's last argv element — that is how
dash-prompt tests prove the prompt arrived intact.