I'm giving texture readback and shared contexts another try. It seems things have improved, but here is something I don't understand.
In the following patch I render twice on one render context, both times with a different shader. When I enable the metro I first see a stream of error messages. But once I assign the captured texture to an object, the errors disappear.
Steps to reproduce are inside the patch. It would be great if someone could explain me whether I do something wrong or this is a bug in jitter.
(note, please save and open before use)