fix(cursor): make close() idempotent on sync and async cursors

Add an early-return guard when the cursor is already closed so a
second close() is a no-op. This matches Connection.close() and the
convention used by sqlite3 / psycopg. The sync path also avoids a
spurious _check_thread() call from a finalizer thread during
interpreter shutdown.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitedbapi/aio/cursor.py

@@ -187,7 +187,12 @@ async def fetchall(self) -> list[tuple[Any, ...]]:
         return result
 
     async def close(self) -> None:
-        """Close the cursor."""
+        """Close the cursor.
+
+        Idempotent: a second call is a no-op.
+        """
+        if self._closed:
+            return
         self._closed = True
         self._rows = []
         self._description = None

src/dqlitedbapi/cursor.py

@@ -309,7 +309,14 @@ def fetchall(self) -> list[tuple[Any, ...]]:
         return result
 
     def close(self) -> None:
-        """Close the cursor."""
+        """Close the cursor.
+
+        Idempotent: a second call is a no-op. PEP 249 mandates that
+        operations on a closed cursor raise an Error, but the close
+        itself is permitted to be repeated.
+        """
+        if self._closed:
+            return
         self._connection._check_thread()
         self._closed = True
         self._rows = []

tests/test_async_cursor.py

@@ -41,6 +41,14 @@ async def test_close_marks_cursor_closed(self) -> None:
         await cursor.close()
         assert cursor._closed
 
+    @pytest.mark.asyncio
+    async def test_close_is_idempotent(self) -> None:
+        conn = AsyncConnection("localhost:9001")
+        cursor = AsyncCursor(conn)
+        await cursor.close()
+        await cursor.close()  # must not raise
+        assert cursor._closed
+
     @pytest.mark.asyncio
     async def test_fetchone_on_closed_cursor_raises(self) -> None:
         conn = AsyncConnection("localhost:9001")

tests/test_cursor.py

@@ -35,6 +35,13 @@ def test_close_marks_cursor_closed(self) -> None:
         cursor.close()
         assert cursor._closed
 
+    def test_close_is_idempotent(self) -> None:
+        conn = Connection("localhost:9001")
+        cursor = Cursor(conn)
+        cursor.close()
+        cursor.close()  # must not raise
+        assert cursor._closed
+
     def test_fetchone_on_closed_cursor_raises(self) -> None:
         conn = Connection("localhost:9001")
         cursor = Cursor(conn)