Macro subgroup_header_accessor 

macro_rules! subgroup_header_accessor {
    (
        $(#[$meta:meta])*
        $name:ident -> $ret:ty;
        $(
            [ $( $variant:ident @ $feat:literal ),+ $(,)? ] => |$h:ident| $body:expr
        ),+ $(,)?
    ) => { ... };
}

Generates one uniform AnySubgroupHeader accessor.

Bodies are written once per group of drafts that share one; every arm is #[cfg]-gated on its own draft feature and a catch-all closes the match, so a single-draft build and a zero-draft build both compile — the same shape dispatch_enum! generates for draft().