Drop on `await` point

Ddystopia:

Hello, what do you think about potentially adding a language feature that will allow forcing synchronous drop at the await boundary, with an error if value is used afterwards

can you expand on what that would look like ?

Ddystopia:

There exists lots of data structures that rely on the fact that they are not being held across await point, and that might help with it.

can you name some ? currently there is no way to ensure one is not held across an await point afaik.

i guess a way that could work is a recursive auto trait that is mutually exclusive with Future ? that's a bit strange. should it cover Coroutines as well ?