feat(bindings): expose new IndexConfig fields in Python and Node.js (#3534)

## Summary

Surfaces the rich per-index metadata added in #3497 to the Python and
Node.js language bindings. Closes #3495.

New optional fields exposed on `IndexConfig` in both bindings:

- `index_uuid` / `indexUuid` — UUID of the first index segment
- `type_url` / `typeUrl` — protobuf type URL for the index
- `created_at` / `createdAt` — creation timestamp (milliseconds since
Unix epoch)
- `num_indexed_rows` / `numIndexedRows` — rows covered by the index
- `num_unindexed_rows` / `numUnindexedRows` — rows not yet indexed
- `size_bytes` / `sizeBytes` — total index file size in bytes
- `num_segments` / `numSegments` — number of index segments
- `index_version` / `indexVersion` — on-disk format version
- `index_details` / `indexDetails` — type-specific JSON details string

All fields are `None`/`undefined` for remote tables (which don't yet
surface this metadata through the server response).

## Changes

- `python/src/index.rs`: extend `IndexConfig` pyclass; update `From`
impl; update `__getitem__`
- `python/python/lancedb/_lancedb.pyi`: add type hints for new fields
- `python/python/tests/test_table.py`: new `test_index_config_fields`
test
- `nodejs/src/table.rs`: extend `IndexConfig` napi struct; update `From`
impl
- `nodejs/__test__/table.test.ts`: new test; update existing `toEqual`
assertions to `expect.objectContaining` to accommodate new fields

## Test plan

- [x] Python: `uv run --extra tests pytest
python/tests/test_table.py::test_index_config_fields`
- [x] Node.js: `pnpm test __test__/table.test.ts`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

python/python/lancedb/_lancedb.pyi

@@ -1,4 +1,4 @@
-from datetime import timedelta
+from datetime import datetime, timedelta
 from typing import Dict, List, Optional, Tuple, Any, TypedDict, Union, Literal
 
 import pyarrow as pa
@@ -259,6 +259,15 @@ class IndexConfig:
     name: str
     index_type: str
     columns: List[str]
+    index_uuid: Optional[str]
+    type_url: Optional[str]
+    created_at: Optional[datetime]
+    num_indexed_rows: Optional[int]
+    num_unindexed_rows: Optional[int]
+    size_bytes: Optional[int]
+    num_segments: Optional[int]
+    index_version: Optional[int]
+    index_details: Optional[Any]
 
 async def connect(
     uri: str,

python/python/tests/test_table.py

@@ -2566,6 +2566,55 @@ def test_create_index_nested_field_paths(mem_db: DBConnection):
     assert fts_results[0]["payload"]["text"] == "document 44"
 
 
+def test_index_config_fields(mem_db: DBConnection):
+    """Test that IndexConfig exposes the new rich metadata fields."""
+    vec_array = pa.array(
+        [[float(i), float(i + 1)] for i in range(300)], pa.list_(pa.float32(), 2)
+    )
+    data = pa.Table.from_pydict({"x": list(range(300)), "vector": vec_array})
+    table = mem_db.create_table("index_config_fields", data=data)
+    table.create_scalar_index("x", index_type="BTREE")
+    table.create_index(
+        vector_column_name="vector",
+        num_partitions=1,
+        num_sub_vectors=1,
+    )
+
+    indices = {idx.name: idx for idx in table.list_indices()}
+
+    scalar_idx = indices["x_idx"]
+    assert scalar_idx.index_uuid is not None
+    assert isinstance(scalar_idx.index_uuid, str)
+    assert scalar_idx.num_indexed_rows is not None
+    assert scalar_idx.num_indexed_rows == 300
+    assert scalar_idx.num_unindexed_rows is not None
+    assert scalar_idx.num_unindexed_rows == 0
+    assert scalar_idx.num_segments is not None
+    assert scalar_idx.num_segments >= 1
+    assert scalar_idx.size_bytes is not None
+    assert scalar_idx.size_bytes > 0
+    assert scalar_idx.created_at is not None
+    from datetime import datetime, timezone
+
+    assert isinstance(scalar_idx.created_at, datetime)
+    assert scalar_idx.created_at.tzinfo == timezone.utc
+
+    # __getitem__ compatibility
+    assert scalar_idx["index_uuid"] == scalar_idx.index_uuid
+    assert scalar_idx["num_indexed_rows"] == scalar_idx.num_indexed_rows
+    assert scalar_idx["created_at"] == scalar_idx.created_at
+
+    # index_details is parsed from JSON into a Python object
+    assert scalar_idx.index_details is not None
+    assert isinstance(scalar_idx.index_details, dict)
+    assert scalar_idx["index_details"] == scalar_idx.index_details
+
+    vector_idx = indices["vector_idx"]
+    assert vector_idx.index_uuid is not None
+    assert vector_idx.num_indexed_rows == 300
+    assert isinstance(vector_idx.index_details, dict)
+
+
 def test_empty_query(mem_db: DBConnection):
     table = mem_db.create_table(
         "my_table",