C++ destructors and exception safety will likely wreak havoc with any "simple" assembly/longjmp-based solution, unless severely constraining what types you can use within the coroutines.

Not really. I've done it years ago. The one restriction for code inside the coroutine is that it mustn't catch (...). You solve destruction by distinguishing whether a couroutine is paused in the middle of execution or if it finished running. When the coroutine is about to be destructed you run it one last time and throw a special exception, triggering destruction of all RAII objects, which you catch at the coroutine entry point.

Passing uncaught exceptions from the coroutine up to the caller is also pretty easy, because it's all synchronous. You just need to wrap it so it can safely travel across the gap. You can restrict the exception types however you want. I chose to support only subclasses of std::exception and handle anything else as an unknown exception.