grex-plugins-builtin — built-in action primitives and pack-type handlers.
Stub crate reserved for v2 third-party plugin loading. In v1, all
builtins live in grex-core::plugin and are re-exported here for
forward-compat import paths.
M4-A: the Tier-1 action plugins (symlink, env, mkdir, rmdir,
require, when, exec) live inside grex-core::plugin because the
wet-run logic is already there; hoisting the structs alone into this
crate would either force the executor free functions out of
grex-core or create a circular grex-core ↔ grex-plugins-builtin
dependency. This crate therefore re-exports the canonical
[register_builtins] path and the per-action plugin types so
downstream CLI crates can bind to grex_plugins_builtin::... even
while the implementations co-locate with the executor.