Ok, I got a few improvements, and I noticed where the API doesn't work:

* `askTypeCompletion` works inside methods, but not in the class body -> maybe the position should be adjusted to match the "completion" point (right now it uses the beginning of the error marker, which includes the receiver)
* we could offer scope suggestions for `not found: type..` as well  (works fine in my tests)

I'll prepare a pull request shortly. I'd prefer using the API if possible, since using contexts misses implicits (we already use contexts for create method, but here it seems we can avoid using type-checker internals).