3 important + 1 optional findings from code quality review:
1. layout_fingerprint_seed() now lists all 40 SP4 slots and bumps
`ISV_TOTAL_DIM=131` -> `ISV_TOTAL_DIM=171`. Without this, the fail-fast
checkpoint-load guard would not detect the SP4 layout extension —
a binary built against new code would falsely compare-equal to old
checkpoints' fingerprints.
2. Added `SP4_BRANCH_COUNT=4` constant and `debug_assert!(branch <
SP4_BRANCH_COUNT)` in `atom_pos_bound`. Test extended to verify
atom_pos_bound max does not alias into WEIGHT_BOUND family.
3. Refreshed stale content in docs/isv-slots.md: ISV_TOTAL_DIM 96->171,
fingerprint location [37..39)/[47..49) -> [115..117), table entries
[94]/[95] -> [115]/[116].
4. Added `debug_assert!(group < SP4_PARAM_GROUP_COUNT)` to weight_bound,
adam_m_bound, adam_v_bound, wd_rate accessors (symmetric with the
atom_pos_bound change).
cargo check clean, cargo test slot_layout_is_contiguous_and_total_40 passes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
206ebd3558