Function barrier_coverage_gaps_for_driven 

pub fn barrier_coverage_gaps_for_driven(
    graph: &CompiledGraph,
    driven: &[bool],
) -> Vec<BarrierGap>

The same check restricted to the resources driven[resource_index] marks, i.e. the ones a backend executor resolves to a native target and emits transitions for. A backend calls this on the graphs a real session builds, so it covers the input combinations a headless sweep does not reach, and it asserts specifically that everything the backend claims to drive is fully covered. Resources outside the driven set keep whatever synchronisation their encoder owns and are skipped.