## Summary
- Broaden `update_metadata_to` to keep `bool` / `int` / `float` / `None`
and structured values (e.g. PDF `outline` list[dict]) while retaining
string / list[str] merge+dedupe for LLM metadata.
- Fixes document system fields (`_isCurrent`, `_version`,
`_processStatus`) being dropped when parse persists PDF outline via full
`meta_fields` replace.
---------
Co-authored-by: Cursor <cursoragent@cursor.com>