- ensure_index_fresh now rebuilds on ESTIMATOR_INDEX_VERSION mismatch, so a schema bump actually invalidates the cached pickle. - Corrupt meta.json rebuilds instead of crashing. - Index builder no longer falls back to the whole cache dict when per_prefix is missing — that previously treated top-level keys (algo_version, created_at) as prefix stats. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>