Function short_oid 

pub fn short_oid(oid: &str) -> &str

An oid abbreviated for display.

Deliberately not git rev-parse --short: no uniqueness check and no repo access, because every call site wanted a fixed prefix to print, not an abbreviation a reader could resolve. An oid that must be typed back is a different problem — the stack’s ref name uses its own narrower width, which spec/stack.md documents.