Function acquire_project_blocking 

pub fn acquire_project_blocking(
    project_root: &Path,
    timeout: Duration,
) -> Result<LockGuard, LockError>

Blocking variant of acquire_project: waits out a sibling phase’s short critical section, polling with backoff up to timeout. Returns the last Contended error if the sibling still holds the lock at the deadline — after timeout of waiting the holder is more likely wedged than slow, and failing loudly beats mutating the checkout concurrently.