- Cap every inline `//` comment block at 3 lines; distil the rationale
rather than delete it. Enforced by a new comment-guard CI check.
- Fix stale and orphaned rustdoc: broken intra-doc links (renamed or
removed items), doc blocks that had merged onto the wrong item (leaving
the intended item undocumented), and doc-contradicts-code drift.
- Add a doc-links CI check (cargo doc, deny broken intra-doc links) so
both classes of comment rot are caught going forward.