Cursor.close() leaks server-side handle for async commands that were never fetched (#791)

src/databricks/sql/client.py

@@ -1759,9 +1759,18 @@ def cancel(self) -> None:
     def close(self) -> None:
         """Close cursor"""
         self.open = False
-        self.active_command_id = None
         if self.active_result_set:
             self._close_and_clear_active_result_set()
+        elif self.active_command_id is not None:
+            # Async submission whose result was never fetched (no
+            # get_execution_result call), so the result-set close path never
+            # fired. Issue an explicit close_command to free the server-side
+            # statement handle instead of leaking it until session close.
+            try:
+                self.backend.close_command(self.active_command_id)
+            except Exception as exc:
+                logger.warning("close_command on cursor close failed: %s", exc)
+        self.active_command_id = None
 
     @property
     def query_id(self) -> Optional[str]:

tests/e2e/test_driver.py

@@ -342,6 +342,38 @@ def test_execute_async__large_result(self, extra_params):
 
             assert len(result) == x_dimension * y_dimension
 
+    @pytest.mark.parametrize(
+        "extra_params",
+        [
+            {},
+        ],
+    )
+    def test_execute_async__close_without_fetch_frees_handle(self, extra_params):
+        """Closing a cursor whose async command result was never fetched must free
+        the server-side statement handle (issue #791). Otherwise the handle leaks
+        until the session closes."""
+        with self.cursor(extra_params) as cursor:
+            cursor.execute_async("SELECT 1")
+
+            # Capture the server-side command id before we close the cursor.
+            command_id = cursor.active_command_id
+            assert command_id is not None
+
+            backend = cursor.backend
+
+            # Sanity: the handle is live and pollable before close.
+            backend.get_query_state(command_id)
+
+            # User decides not to wait for the result and closes the cursor
+            # without ever calling get_async_execution_result().
+            cursor.close()
+
+            # After close, the server-side handle must have been freed, so a
+            # re-poll of the saved command id should raise a server error.
+            # Pre-fix (leak): this poll succeeds. Post-fix: it raises.
+            with pytest.raises((RequestError, OperationalError, DatabaseError)):
+                backend.get_query_state(command_id)
+
 
 # Exclude Retry tests because they require specific setups, and LargeQueries too slow for core
 # tests