metaphore | Cache slam defense using a semaphore to prevent dogpile | Caching library

The gist of your question:

How can I implement an exception handler for coroutines, such that a second thread can send a signal to a thread evaluating a coroutine, forcing it to yield when its running for too long.

And once more:

How can I successfully write a signal handler that will (yield) correctly so that I can resume the coroutine later?

It seems to me that you are not cleanly separating cooperative and preemptive multitasking, since you seem to want to combine coroutines (cooperative) with time-outs (preemptive). (You also mention threads, but seem to conflate them with coroutines.)

With cooperative multitasking there is no way that you can force anyone else to stop running; hence the moniker "cooperative".

With preemptive multitasking you do not need to yield, because the scheduler will preempt you when your allocated time has run out. The scheduler is also responsible for saving your continuation, but it is not the (scheduler's) current continuation, since the scheduler is wholly separate from the user thread.

Perhaps the closest thing to what you are proposing is simulating preemptive multitasking via polling. Every (simulated) timestep (i.e. a VM instruction) the simulation needs to check whether any interrupts/signals have been received by a running thread and handle them.