#3528 added blob declarations and binary coercion. String values were
still rejected. They now coerce to the blob `uri` child.
```python
table.add([{"id": 1, "image": "s3://bucket/media/cat.jpg"}])
payload = table.fetch_blobs("image", table.search().to_arrow())
```
A URI under a registered base writes with no extra options. An
unregistered URI fails. `allow_external_blob_outside_bases` is a local
escape hatch that stores an absolute URI. It does not register a base.
Remote `add` rejects that flag before making a request. String input
still coerces and is sent as a `uri` struct.
`add_bases` is a follow-up. `merge_insert` does not coerce string blob
input.
### Testing
- `cargo test -p lancedb --test blob_integration`
- `cargo test -p lancedb blob_coerce`
- `cargo test -p lancedb --features remote --lib
add_rejects_external_blob_flag add_string_blob_becomes_uri_struct`
- `cd python && uv run --extra tests pytest python/tests/test_blob.py -k
uri -q`
Co-authored-by: Xuanwo <github@xuanwo.io>