Perform code review checklist for KNHK.

Review checklist:
- [ ] No `unwrap()` or `expect()` in production code
- [ ] All errors properly handled with `Result<T, E>`
- [ ] Guard constraints enforced (max_run_len ≤ 8)
- [ ] Performance within 8-tick budget
- [ ] No placeholders or TODOs
- [ ] Tests cover critical paths
- [ ] OTEL validation confirms behavior
- [ ] Feature-gated optional dependencies
- [ ] Proper resource cleanup
- [ ] Input validation present
- [ ] Error messages provide context

Focus on 80/20 critical path items.

