-- pg_turbovec v2.9.0
--
-- MINOR: adds one new SQL object. Wire format unchanged
-- (MetaPageData::version stays 8) -- existing indexes decode
-- byte-identically, so NO REINDEX is required. The upgrade is in-place:
-- `ALTER EXTENSION pg_turbovec UPDATE TO '2.9.0'` creates the function.
--
-- New: turbovec.index_degradation(regclass) -> TABLE(degraded, lists,
-- n_vectors, scan_fraction, est_slowdown, recovery).
--
-- Phase Z1 made IVF degradation observable and Phase Z4 made the planner
-- cost it; neither told an operator the SIZE of the problem, which is what
-- decides whether to act. This quantifies it: a degraded index reports
-- scan_fraction = 1.0 (it reads everything) and est_slowdown = lists/probes,
-- plus the REINDEX command naming the index.
--
-- Reads only the meta page (one buffer hit), so it is safe to poll from
-- monitoring.