The 3-phase retain pipeline (914ba796) introduced several regressions:
1. **Per-content tags lost** — streaming pipeline used `contents[0].tags`
for ALL chunks, breaking tag-based visibility. Fixed by tracking
chunk-to-content mapping so each chunk uses its source content's tags.
2. **Multi-document batches broken** — batches with per-content
`document_id` values were merged into a single document. Fixed by
grouping by document_id and processing each group independently.
3. **Migration ID collision** — `d6e7f8a9b0c1` was used by both
`drop_documents_metadata` and `case_insensitive_entities_trgm_index`.
Renamed trgm migration to `e8f9a0b1c2d3`, fixed chain, added missing
schema prefix on DROP INDEX.
4. **Graph entity inheritance** — `get_graph_data` queried entities for
observation IDs only, but observations inherit entities from source
memories. Fixed by querying `all_relevant_ids`.
5. **Docstring false positives** — link_utils.py docstrings triggered
the SQL schema safety test's unqualified table reference check.
6. **Config test count** — `retain_chunk_batch_size` added to
`_CONFIGURABLE_FIELDS` without updating the test assertion.
7415ebff7c