Function tracker_body 

pub fn tracker_body(original: &str, parts: &[(String, i64)]) -> String

A split parent’s body: what it said, then the checklist of its parts.

The original text comes through untouched, byte for byte, and the checklist is appended after it. This is the one place spar rewrites prose somebody else wrote, and appending is the only shape of that which cannot lose any of it.

Each line carries its #N, which is what makes the parent an ordinary tracker: a checklist whose items are issue numbers.