-- pg_turbovec v1.27.0 -- Phase Q-0: de-duplicate the on-disk codes
-- storage (drop the persisted SIMD-blocked chain).
--
-- This file is a *reference mirror*. The authoritative install script
-- is generated by `cargo pgrx schema`.
--
-- WIRE-FORMAT CHANGE -- REINDEX REQUIRED for all pre-v7 indexes.
--
-- Every prior version persisted each vector's quantized codes TWICE:
-- the row-major bit-plane `packed_codes` chain AND the SIMD-`blocked`
-- chain (the output of `pack::repack(packed_codes, ...)`). That
-- doubled the dominant O(n) storage term. Since the blocked layout is
-- a PURE FUNCTION of the packed codes, v7 drops the blocked chain
-- entirely and recomputes it once per backend at index-open via
-- `pack::repack` (the same one-time compute a pre-Phase-P index
-- already paid on first scan; per-query cost is unchanged). This
-- roughly HALVES the per-vector on-disk footprint -- clearing the
-- storage blocker for large single-node indexes.
--
-- This is NOT additive. A v7 relfile has no blocked chain, so it is
-- not byte-compatible with any prior version FOR ANY KIND
-- (single-vector, ColBERT, or graph). Unlike the v4->v5->v6 additive
-- per-kind bumps, EVERY kind now emits wire version 7 (the `kind` byte
-- still discriminates single/colbert/graph). A pre-v7 index (v1..v6)
-- is detected by `MetaPageData::is_legacy_v6()` (version < 7) and
-- `ambeginscan` (and amgettuple's first fetch) raises a clear ERROR
-- that NAMES the index with a `HINT: REINDEX INDEX <name>;` -- never
-- silent corruption.
--
-- No SQL surface change (no operators, types, functions, GUCs, or
-- opclasses added or removed) -- this is a storage-layout change only.
-- Scan results (recall, ordering) are IDENTICAL to before for a
-- freshly-built index: the blocked layout recomputed from the packed
-- codes is bit-identical to the layout that used to be persisted.
--
-- Migration:
--   1. `ALTER EXTENSION pg_turbovec UPDATE TO '1.27.0';`
--   2. `REINDEX INDEX <name>;`  -- once per turbovec index, ANY kind.
-- Until an index is REINDEXed under v7, scans against it ERROR with
-- the REINDEX hint (they do NOT return wrong results). See
-- docs/UPGRADING.md.