fix(python): return the session supplied to LanceDBConnection (#4433)

LanceDBConnection.session read AsyncConnection.session, but
AsyncConnection has no session attribute, so access raised
AttributeError. Store the session passed to the constructor and return
that object.

Assisted by Cursor (Grok).

Co-authored-by: Preston Zhao <195942578+canyang25@users.noreply.github.com>

python/python/lancedb/db.py

@@ -1300,6 +1300,10 @@ class LanceDBConnection(DBConnection):
         self.storage_options = storage_options
         self._manifest_enabled = manifest_enabled
         self._namespace_client_properties = namespace_client_properties
+        # The native connection does not expose the Python Session wrapper.
+        # Keep the object supplied by the caller so this property stays
+        # synchronous for debugger inspection.
+        self._session = session
         if _inner is not None:
             self._conn = _inner
             # Native-derived wrappers resolve this in their async reconstruction
@@ -1366,7 +1370,12 @@ class LanceDBConnection(DBConnection):
 
     @property
     def session(self) -> Optional[Session]:
-        return self._conn.session
+        """Return the session supplied when this connection was opened.
+
+        None when the caller did not pass a session, including connections
+        reconstructed with :meth:`from_inner`.
+        """
+        return self._session
 
     @property
     def uri(self) -> str:

python/python/tests/test_db.py

@@ -86,6 +86,7 @@ def test_sync_debugger_inspection_does_not_use_background_loop(tmp_path, monkeyp
 
     assert members["uri"] == str(tmp_path)
     assert members["read_consistency_interval"] is None
+    assert members["session"] is None
     assert repr(db) == f"LanceDBConnection(uri={str(tmp_path)!r})"
     assert repr(table) == f"LanceTable(name='test', _conn={db!r})"
 
@@ -105,6 +106,8 @@ def test_read_consistency_interval_does_not_use_background_loop(tmp_path, monkey
 
     assert db.read_consistency_interval == consistency_interval
     assert db_from_inner.read_consistency_interval == consistency_interval
+    assert db.session is None
+    assert db_from_inner.session is None
 
 
 def test_ingest_pd(tmp_path):

python/python/tests/test_session.py

@@ -36,3 +36,13 @@ def test_session_cache_configuration(tmp_path):
     assert final_cache_size > initial_cache_size  # Cache should have grown
     assert final_cache_items >= initial_cache_items  # Items should not decrease
     assert initial_cache_size < index_cache_size + metadata_cache_size
+
+
+def test_connection_session_returns_supplied_session(tmp_path):
+    """Sync connections must expose the session they were opened with."""
+    db = lancedb.connect(tmp_path)
+    assert db.session is None
+
+    session = lancedb.Session()
+    db = lancedb.connect(tmp_path, session=session)
+    assert db.session is session