agent/docs/architecture/rag_chunks_column_audit.md

column	used_by	safe_to_drop	notes
layer	USED_BY_CODE_V2, USED_BY_DOCS_INDEXING	no	Core selector for C0-C3 and D1-D4 queries.
title	USED_BY_CODE_V2, USED_BY_DOCS_INDEXING	no	Used in lexical ranking and prompt evidence labels.
metadata_json	USED_BY_CODE_V2, USED_BY_DOCS_INDEXING	no	C2/C0 graph lookups and docs metadata depend on it.
span_start, span_end	USED_BY_CODE_V2	no	Needed for symbol-to-chunk resolution and locations.
symbol_id, qname, kind, lang	USED_BY_CODE_V2	no	Used by code indexing, ranking, trace building, and diagnostics.
repo_id, commit_sha	USED_BY_CODE_V2, USED_BY_DOCS_INDEXING	no	Used by indexing/cache and retained for provenance.
entrypoint_type, framework	USED_BY_CODE_V2	no	Used by C3 filtering and entrypoint diagnostics.
doc_kind, module_id, section_path	USED_BY_DOCS_INDEXING	no	Still written by docs indexing and covered by docs tests.
artifact_type, section, doc_version, owner, system_component, last_modified, staleness_score	USED_BY_DOCS_INDEXING	no	File metadata still flows through indexing/cache; left intact for now.
rag_doc_id	UNUSED	yes	Written into rag_chunks only; no reads in runtime/indexing code.
links_json	UNUSED	yes	Stored in rag_chunks only; reads exist for rag_chunk_cache, not rag_chunks.