how to adapt to callback style API

the referenced document says to use

async_xxx(param, callbackhandler)

to

co_await async_xxx(param);

but, that kind of refactoring only works with asio.

we have some old lib that accepts callbacks. now I want to call that old lib function and "co_await" for the callback to be invoked.

hint: I warpped the Executor for the old lib, so the old lib and async_simple runs in the same Executor. I need a way to convert
"lazy<>" to some old style callbacks. and let that callback to resume the calling lazy<>

The issue names no files or tests. Start by reading the async_simple lazy<> and Executor APIs, then compare them with the old library's callback contract. Done would require an agreed, tested way to bridge callback completion to a suspended lazy<> coroutine.

Written by the indexing model from the issue text.