Function is_plugin_peer 

pub fn is_plugin_peer(
    peer_uid: u32,
    peer_gids: &[u32],
    plugin_user_uid: Option<u32>,
    plugin_gid: Option<u32>,
) -> bool

Whether a connecting peer is on the plugin plane: the shared plugin user, or any process carrying PLUGIN_GROUP as its primary or a supplementary group. Such a writer is autonomous by construction, so it is gated as an injector whether or not it declares itself one; a self-declaration only binds the cooperating ones.

Pure over the kernel-reported credentials so the decision is testable without a second uid.