Function is_lock_failure 

fn is_lock_failure(stderr: &str) -> bool

Whether git refused the fetch because a ref lock it needed is held - by another git in the same checkout, or by a killed child that left one.

Forge runs one fetch per repository and base branch (a caller joins the run already in flight), so no second fetch of this ref is this process’s: two branches of one repository take different ref locks and may run together. What reaches this check is the user’s git, another forge instance on the same repo, or a stranded lock.