FileVectorIndex persists one binary file per model under index/ with
atomic tmp+rename writes; FileDocumentCatalog persists a single
catalog.json, rebuilding the link graph via WikiLinks.Extract on every
upsert. Both start empty and report health Ok with a reset detail if
their file on disk is corrupt, rather than crashing.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
