Type Alias SubscribeSetSecurityPlan 

pub type SubscribeSetSecurityPlan = (u64, Option<NonZero<u32>>, Vec<(i32, SubBitOptions)>);

Per-security input for one backend CMD6211 SubscribeSetReq.

Backend owns the protobuf encoding, while this domain tuple owns the stable command-plan shape: stock id, optional broker id, and all requested subscribe bits/options for that stock.