Smoke-15: be-doc i_documented(files=["README.md"]) → choreographer
doc.py stamped `existing.documents = files` (a list[str]) onto
Task.documents. Task.documents is list[DocRef] persisted as dicts —
list_docs does DocRef(**d), _get_existing_doc_ref does d.get("path"),
the RAG indexer does d.get("path"). A bare string 500'd GET /docs
("TypeError: DocRef() argument after ** must be a mapping, not str")
during be-pm's PR review and would AttributeError the indexer.
Fix at source: new _doc_refs_for builds proper DocRef dicts
(path, title=filename, doc_type, created_by/at, updated_by/at) at the
i_documented stamp. Defensive read: new _coerce_doc_ref tolerates
dict / DocRef / bare-string / rejects unknown — applied at
list_docs and _get_existing_doc_ref so legacy/corrupted rows can't
500. _add_doc_to_task (docs-route write path, not the gateway flow
that broke) left as-is per scope.
