-- 2.7.3 — 1-bit BQ frontier MEASURED + an empty-table insert fix.
--
-- 1. BUG FIX (real, found on a corpus host, not by a test): a bit_width = 1
--    index created on an EMPTY table rejected its first INSERT with
--    "dim mismatch -- index expects 0, row has N". The empty build stamps
--    dim = 0 (no rows, no reloption-pinned dim) and insert_bq_row read the dim
--    from the meta page. The flat path never had this because it takes the dim
--    from the incoming row; the BQ path now does too, seeding the mean as
--    zeros for the 0-row case (a 1-row corpus mean IS that row, so every
--    centred coordinate is 0 -- what a rebuild would produce). Every in-tree
--    BQ fixture indexed an already-populated table, which is why all of them
--    missed it. Regression test covers the exact failing order AND asserts a
--    wrong-dim row is still rejected once the dim is pinned.
--
-- 2. The 1-bit sign-BQ recall/storage/latency frontier is now MEASURED and
--    published, closing the last "not yet published" claim in the README.
--    arnold (AVX2, latency-publishable per AGENTS.md), PG 17.9, 250k x 1024-d
--    Cohere-wiki, 100 held-out queries, exact in-DB ground truth, postmaster
--    and driver pinned to P-cores 2-5, all 24 configs verified to use a real
--    Index Scan.
--
--    Storage: 1-bit is 3.98x smaller than 4-bit, 2.02x smaller than 2-bit.
--    Cost: at matched recall it is 2.7-6.1x slower and needs a 25x WIDER
--    exact-rerank window than 2-bit to clear R@10 >= 0.99 (800 vs 32).
--    All four predictions registered BEFORE the run held, including P2, whose
--    falsification condition would have meant the hi_dim_rerank 1-bit
--    special-case was unnecessary -- the data justifies it.
--
--    Also found: R@100 for 1-bit tops out at 0.981 and is 0.948 at the auto
--    default, so 1-bit degrades faster at DEPTH than at k=10 -- budget a
--    wider window if you paginate past the top 10.
--
-- No wire-format change (stays v8), no SQL surface change, no REINDEX.
-- This migration is intentionally empty.