Function compose_prefix 

pub fn compose_prefix(prefix: &str, value: &str) -> String

Glue prefix onto value without doubling it: a value that already spells the prefix out comes back unchanged.

Two coordinates of one tag compose this way — a monorepo namespace onto a per-crate track (subproject1/ + core-v), and tag.tag_prefix onto the tag name git reported (v + v1.2.3). Both are idempotent because the operator may already have written the composed form, and prepending blindly turns v1.2.3 into vv1.2.3.