readbacks property
Every readback asked for, in order: which texture and which region.
Recorded because the thing worth testing about a readback off a device is that it was asked for at all, of the right texture, for the right pixel — what comes back is the backend's business, and this one has no pixels.
Implementation
final List<({TextureHandle texture, ScreenRect region})> readbacks =
<({TextureHandle texture, ScreenRect region})>[];