Function acquire_shadow_lock

atomic-cli/src/commands/git/shadow.rs:111–135

Acquire the repo-scoped shadow-commit lock, or return `None` (a no-op skip) if a shadow materialize/commit is already in flight (SPEC §4.3 / Principle 5). Non-blocking: rather than queueing (which would hang a turn-end hook), the contended case is a logged no-op — the in-flight operation owns this commit. The returned guard must be held for the whole stage → validate → commit sequence; dropping i

(
    repo: &Repository,
    repo_root: &Path,
    view: &str,
)

/// sequence; dropping it releases the lock. Acquire it **outermost**, before any
/// staging or DB write.
pub(crate) fn acquire_shadow_lock(
    repo: &Repository,
    repo_root: &Path,
    view: &str,
) -> CliResult<Option<std::fs::File>> {
    match repo
        .try_lock_shadow_commit()
        .map_err(CliError::Repository)?
    {
        Some(guard) => Ok(Some(guard)),
        None => {
            if std::io::stderr().is_terminal() {
                print_info("Another shadow materialize is in flight; skipping this push.");
            } else {
                append_shadow_log(
                    repo_root,
                    "shadow-lock:contended",
                    view,
                    "another shadow materialize in flight",
                );
            }
            Ok(None)
        }
    }
}

/// Stage the current working copy for a shadow commit, run the pre-commit
/// Validator, and return the candidate git tree OID.