[gouyt13]

Summary

Share IVF/HNSW removal-ID validation and reuse four identical binding documentation strings. Keep conversion order, byte-safe reads, error messages, public documentation, and GIL/access-guard boundaries unchanged.

Give QG save/load one private definition of the format marker/version, and extract centroid-graph preparation from QGAssigner without changing build policy or cache publication order. No public API, saved-index format, or dependency changes.

Testing

• Portable C++ unit/reference suite: 367 passed; the OpenMP binding test skipped in the default run passed separately. Frozen core v1 consumer passed.
• Rebuilt and verified installed wheel: 762 Python tests passed, two platform-only checks skipped (standard wheel test scope).
• Before/after comparison: 50 public documentation entries, raw/4/8-bit QG serialized bytes/search results, and fixed-seed clustering results unchanged.
• Independent review found no blocking issues and reran 193 targeted Python tests successfully, including documentation and persistence comparisons.
• Full configured clang-tidy, C++ formatting, Python formatting/lint, and git diff --check passed.
• No additional cross-platform runtime, sanitizer, or performance validation; no performance claim.