Function is_transient_error 

pub fn is_transient_error(err: &RunError) -> bool

Default transient error check for jj/git.

Retries on:

• NonZeroExit with "stale" in stderr — “The working copy is stale” (jj)
• NonZeroExit with ".lock" in stderr — Lock file contention (git/jj)

Spawn failures and timeouts are never treated as transient.