Function publish 

pub fn publish(
    repo: &Path,
    project_state: &Path,
    feature: &str,
    tmp: &Path,
) -> Result<Option<String>, String>

Publishes a finished feature’s held-out sets in the private store (every task is closed then): publish_closed over the tasks the branch tip closes. Never pushed here; speccoder pr pushes it. Ok(None) when no closed task names a stored set.