Expand description
grex exec — run an arbitrary command inside a pack root.
Resolves the pack root via the shared cwd-default helper (same as
sync / teardown). The first positional element is the program
name; subsequent elements are passed verbatim. Stdio is inherited
in human mode and captured under --json. The child’s exit code
is propagated, clamped at 125 so it never collides with the sync
exit-code band (1/2/3).