Function select_public_key_focus_segment_kernel 

pub fn select_public_key_focus_segment_kernel(
    ready: SegmentGroups,
    public_key_block: b6,
    public_key_inflight: bool,
) -> SegmentSelection

Select a ready segment in an eight-block endpoint-stream lookahead window.

Before public-key block n issues the window begins at n; while n is in flight it begins at n + 1. The first ready segment in blocks from the window start through start + 7 wins. Each selected segment immediately becomes in flight and cannot issue again until its 64-cycle response, so the lookahead cannot continuously monopolize issue slots; the rotating general selector consumes the gaps. The scan saturates at block 33 and never wraps.