Function linked_runtime_bytes 

pub fn linked_runtime_bytes(runtime: &BTreeSet<&'static str>) -> usize

The runtime files one bundle actually links, in bytes.

The set comes from Bundle::runtime, which is the same closure the emitter used to decide the import list — one decision rather than two that have to agree. This is what makes “ships nothing it does not use” a measured property here rather than an assumption baked into a sum.