Why: string writes of .docx/.xlsx/.pdf produce files that will not open,
and generated binary artifacts were skipped by search entirely.
Evidence: go test ./... 19 packages ok. Office extensions are refused
with a pointer to run_python plus register_artifact. A docgen docx is
searchable after WriteArtifact; unparseable bytes are not indexed.
Impact: write_artifact and fs_write_file no longer accept those
extensions. Text artifacts index as before. Merge after the interpreter
PR so the error text names tools that exist.
Refs: task feature/binary-doc-index; supersedes Dev #99 / Backend #27
Co-authored-by: Cursor <cursoragent@cursor.com>
weichen
