Function execute_history_observed 

pub fn execute_history_observed(
    request: &HistoryRequest,
    observe: &mut dyn FnMut(HistoryProgress<'_>) -> bool,
) -> HistoryResult

execute_history with a progress observer. observe is called immediately BEFORE each feature the run executes (cached replays are not reported); returning false stops the run at that boundary — the feature is not executed, nothing after it runs, and the result holds what was built so far. The boundary is the only cooperative stop the kernel offers: nothing inside a feature (a boolean, a blend, a sew) checks anything.

The cache bookkeeping is untouched by an early stop: the entries of the features that did run are as valid as after a full run, and the entries of the ones that did not were retained as parse-only exactly as under a stop_before_id, so the next full run replays the former and executes the latter.