"Cancel scope stack corrupted" is thrown when recursion depth exceeded

The following code:

import trio

def f():
    with trio.move_on_after(1):
        f()

trio.run(f)

Fails with:

RuntimeError: Cancel scope stack corrupted: attempted to exit <trio.CancelScope at 0x7f451b880130, active, deadline is 1.00 seconds from now> in <Task '<init>' at 0x7f451ba35ed0> that's still within its child <trio.CancelScope at 0x7f451b880210, active, deadline is 1.00 seconds from now>

Way up the stack trace, there's also a RecursionError: maximum recursion depth exceeded in comparison. Neither of those are the errors I'd expect; I'd expect a simple RecursionError: maximum recursion depth exceeded.

Reproduce the failure with the recursive f(), trio.move_on_after(), and trio.run() entry points shown in the issue, then trace how recursion exhaustion is handled while nested cancel scopes exit. Done means the example raises the expected plain RecursionError instead of the cancel-scope corruption RuntimeError.