The dispatch-gate tests spawned where.exe and powershell and pointed the gate
at the checked-in .cmd wrappers. On non-Windows they now resolve executables
with which, run commands through sh, write a fake gh as an executable script,
and stand in for git.cmd/gh.cmd with sh shims that exec the same Node proxies
(git-proxy.mjs, gh-proxy.mjs). Windows behavior is unchanged.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>