Function versions_compatible 

pub fn versions_compatible(a: &str, b: &str) -> bool

Two protocol version strings interoperate when they share a major family — the substring up to the first .. So contextgraph/1.0-draft and contextgraph/1.0 interoperate (both contextgraph/1), while contextgraph/2.0 does not. This is what allowed the public v1.0 freeze to drop the -draft suffix without a flag day (SPEC.md).