fix: address review issues for immediate check-phase refactor
- Fix duplicate "2d" phase comment numbering (rejections → "2e")
- Add clarifying comment on IMM_IDX_COUNT vs IMM_IDX_REF_COUNT gate
- Fix misleading test comment about immediate nesting semantics
- Enable 2 newly-passing node compat tests (invalid-clear, throw-when-cb-not-function)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
