`sleep()` hangs indefinitely when using a custom clock

Tested on 0.32 and the current master.

MRE:

import trio
import trio.testing


class FooMockClock(trio.abc.Clock):
    def __init__(self) -> None:
        self._clock = trio.testing.MockClock(autojump_threshold=0)

    def current_time(self) -> float:
        return self._clock.current_time()

    def deadline_to_sleep_time(self, deadline: float) -> float:
        return self._clock.deadline_to_sleep_time(deadline)

    def start_clock(self) -> None:
        self._clock.start_clock()


async def main():
    print(trio.current_time())
    await trio.sleep(2)
    print(trio.current_time())


if __name__ == '__main__':
    print("MockClock")
    trio.run(main, clock=trio.testing.MockClock(autojump_threshold=0))
    print("FooMockClock")
    trio.run(main, clock=FooMockClock())

Output:

MockClock
0.0
2.0
FooMockClock
0.0
< hangs indefinitely >

I expected the second run() to behave exactly the same as the first. What am I doing wrong?

Also, if I copy-paste trio.testing.MockClock verbatim to this script and use that, the execution crashes - may be related:

Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2813, in unrolled_run
    assert isinstance(runner.clock, _core.MockClock)
AssertionError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/bogdan/wb/github/nucypher-async/t_new.py", line 185, in <module>
    trio.run(main, clock=MockClock(autojump_threshold=0))
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2538, in run
    timeout = gen.send(next_send)
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2951, in unrolled_run
    raise TrioInternalError("internal error in Trio - please file a bug!") from exc
trio.TrioInternalError: internal error in Trio - please file a bug!
Exception ignored in: <coroutine object Runner.init at 0x106a26500>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2156, in init
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1112, in __aexit__
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1288, in _nested_child_finished
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1252, in _add_exc
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 933, in _cancel
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 501, in recalculate
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1671, in _attempt_delivery_of_any_pending_cancel
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1644, in _attempt_abort
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_io_kqueue.py", line 162, in abort
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_io_kqueue.py", line 184, in abort
ValueError: I/O operation on closed kqueue object
Exception ignored in: <function Nursery.__del__ at 0x105b208b0>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1486, in __del__
AssertionError: 
Exception ignored in: <coroutine object main at 0x106a26570>
Traceback (most recent call last):
  File "/Users/bogdan/wb/github/nucypher-async/t_new.py", line 180, in main
  File "/Users/bogdan/wb/repos/trio/src/trio/_timeouts.py", line 111, in sleep
  File "/Users/bogdan/wb/repos/trio/src/trio/_timeouts.py", line 91, in sleep_until
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 714, in __exit__
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 640, in _close
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2993, in current_task
RuntimeError: must be called from async context
Exception ignored in: <function Nursery.__del__ at 0x105b208b0>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1486, in __del__
AssertionError: 
bogdan@lair ~/w/g/nucypher-async (todo-party) [1]> python t_new.py
0.0
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2813, in unrolled_run
    assert isinstance(runner.clock, _core.MockClock)
AssertionError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/bogdan/wb/github/nucypher-async/t_new.py", line 186, in <module>
    trio.run(main, clock=MockClock(autojump_threshold=0))
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2538, in run
    timeout = gen.send(next_send)
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2951, in unrolled_run
    raise TrioInternalError("internal error in Trio - please file a bug!") from exc
trio.TrioInternalError: internal error in Trio - please file a bug!
Exception ignored in: <coroutine object Runner.init at 0x106ade500>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2156, in init
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1112, in __aexit__
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1288, in _nested_child_finished
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1252, in _add_exc
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 933, in _cancel
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 501, in recalculate
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1671, in _attempt_delivery_of_any_pending_cancel
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1644, in _attempt_abort
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_io_kqueue.py", line 162, in abort
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_io_kqueue.py", line 184, in abort
ValueError: I/O operation on closed kqueue object
Exception ignored in: <function Nursery.__del__ at 0x105bd8820>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1486, in __del__
AssertionError: 
Exception ignored in: <coroutine object main at 0x106ade570>
Traceback (most recent call last):
  File "/Users/bogdan/wb/github/nucypher-async/t_new.py", line 181, in main
  File "/Users/bogdan/wb/repos/trio/src/trio/_timeouts.py", line 111, in sleep
  File "/Users/bogdan/wb/repos/trio/src/trio/_timeouts.py", line 91, in sleep_until
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 714, in __exit__
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 640, in _close
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 2993, in current_task
RuntimeError: must be called from async context
Exception ignored in: <function Nursery.__del__ at 0x105bd8820>
Traceback (most recent call last):
  File "/Users/bogdan/wb/repos/trio/src/trio/_core/_run.py", line 1486, in __del__
AssertionError: 

Run the supplied MRE first, then inspect the clock handling in src/trio/_core/_run.py and the sleep path in src/trio/_timeouts.py. Review the related assertion and cleanup failures in src/trio/_core/_io_kqueue.py. Done means a custom clock and a copied MockClock no longer hang, trigger the internal assertion, or produce the shown cleanup errors.