fix connection drain

Signed-off-by: Aykut Bozkurt <aykut.bozkurt@snowflake.com>

Author: sfc-gh-abozkurt

pg_lake_engine/src/pgduck/client.c

@@ -647,6 +647,27 @@ CancelRunningCommandOnConnection(PGconn *conn)
 		return;
 	}
 
+	/*
+	 * Try a non-blocking drain before resorting to cancel.  When a query has
+	 * already completed (e.g. with an error) but the ereport(ERROR) unwound
+	 * the stack before libpq consumed ReadyForQuery, the connection still
+	 * appears ACTIVE.  A single PQconsumeInput + drain is usually enough to
+	 * process the buffered ReadyForQuery and transition to IDLE, avoiding a
+	 * spurious cancel that can corrupt DuckDB session state.
+	 */
+	if (PQtransactionStatus(conn) == PQTRANS_ACTIVE &&
+		PQconsumeInput(conn))
+	{
+		while (!PQisBusy(conn))
+		{
+			PGresult   *res = PQgetResult(conn);
+
+			if (res == NULL)
+				break;
+			PQclear(res);
+		}
+	}
+
 	if (PQtransactionStatus(conn) == PQTRANS_ACTIVE)
 	{
 		/* a query is still running, cancel it */

pg_lake_spatial/tests/pytests/test_gdal.py

@@ -203,11 +203,7 @@ def test_gdal_zip_gml(
     # Querying is currently not supported because WKB is converted by DuckDB
     # Error messages reflect different DuckDB spatial versions
     error = run_query("SELECT shape FROM test_gdal.fdw", user_conn, raise_error=False)
-    assert (
-        "Geometry type 10 not supported" in error
-        or "'MULTICURVE' is not supported" in error
-        or "Unsupported geometry type in WKB" in error
-    )
+    assert "Unsupported geometry type in WKB" in error
 
     user_conn.rollback()