Macro subcommands 

macro_rules! subcommands {
    (
		[$argtype:ty => $prep:expr]
		$(
			$(#[cfg($cfg:meta)])*
			$(#[clap($clap:meta)])*
			$modname:ident => $enumname:ident($argname:ident)
		),+
	) => { ... };
}

Wire up a subcommand level.

Generates an Action enum (one variant per subcommand), and a run(args, ctx) dispatcher. The prep closure runs before dispatch: it returns the chosen Action along with a Context that has been populated with this level’s args (and anything else the level wants to provide). Each variant then dispatches to <modname>::run(sub_args, ctx).

Every level uses the same (args, ctx) signature, so contexts compose across arbitrary nesting depth and downstream handlers can extract any ancestor’s args by type via ctx.require::<T>().