-- pg_turbovec v2.10.0
--
-- MINOR: new GUC + changed runtime behaviour. NO SQL-surface change and NO
-- wire-format change (MetaPageData::version stays 8) -- existing indexes
-- decode byte-identically and NO REINDEX is required. `ALTER EXTENSION
-- pg_turbovec UPDATE TO '2.10.0'` is sufficient.
--
-- Phase Z5 Route A: an IVF index no longer loses its cell layout on the
-- first INSERT.
--
-- `aminsert` cannot place a row into its cell without an O(n) reshuffle, so
-- appended rows land at the tail, outside every cell. Previously the flush
-- dropped the coarse-centroid and cell-directory chains entirely, so one
-- commit turned the index into an O(n) flat scan until REINDEX. The flush
-- now writes those chains back UNCHANGED and the scan additionally sweeps
-- the tail exhaustively -- results stay EXACT, only latency is affected.
--
-- No new meta field is needed: the delta length is DERIVABLE as
-- `n_live - cell_directory.total_vectors()`, because existing rows keep
-- their slot (UPDATE writes in place) and inserts append at the tail.
--
-- New GUC: turbovec.ivf_max_delta_pct (default 10, range 0..=100). Bounds
-- the append region as a percent of cell-partitioned rows. Past the bound
-- the index degrades to flat and reports it exactly as before. Setting it to
-- 0 restores pre-2.10.0 behaviour byte-for-byte.