Function execute_history 

pub fn execute_history(request: &HistoryRequest) -> HistoryResult

Run a whole feature history incrementally: build the expression env once, then walk the ordered features. A CLEAN feature (see the cache section above) replays its cached result; a DIRTY one re-executes (its old outputs are freed first). On a feature error, record it and HALT (abort-on-error); errored results are never cached. Never panics.