Captures only a managed toplevel's surface tree, independently of its workspace, occlusion, animations and output transform. The compositor advertises this interface only to its native portal executable. Capture requires session opt-in and fails while locked. Window IDs are compositor lifetime IDs and never resolve to replacement windows. The two unsigned words encode a 64-bit window ID (high word first). A version 1 wlr screencopy frame announces a bounded SHM ARGB8888 snapshot. It fails if the target has closed, capture is unavailable, or the outstanding snapshot budget is exhausted. Resize after the buffer announcement does not change this frame's dimensions. Overlay cursor is zero for hidden and one for embedded. Sent before this frame's failed event if the bounded snapshot pool is occupied. Retry a later frame; this does not revoke the window source. Sent before the frame's buffer event. These dimensions describe this captured frame, even if the window resizes before it is copied.