In ConversationHandler we have quite a lot of kwargs regarding @run_async decorated handler callbacks and timeouts.
these are:

• run_async_timeout - The time conversationhandler will wait on a run_async task to complete.
• timed_out_behavior - Here you can specify a list of handlers that will handle the new update if the timeout is exceeded but nog finished on a @run_async decorated callback
• conversation_timeout - If this value is exceeded the conversation will be ended (with an internal job)

in v12 we add a mechanic to give the user an interaction with the conversation on

• conversation_timeout by adding a TIMEOUT state which will be offered the last received update.

Now while debugging I noticed the following things that are a bit off.
If I specify a run_async_timeout=5 it should mean that if the decorated handler takes longer then 5 seconds it will switch to timed_out)behavior but this is not the case.
The waiting for it to complete starts on an incomming new update, within check_update. This means a couple of bad things.

• If I set a timeout for 10 seconds. It could still be running for 3 days and 10 seconds if the next update is only received after 10 days
• If I specify a run_async_timeout=20 and the handler is doing something infinite. The processing of the update_queue will be paused for 20 seconds while waiting.
• see this example: https://gist.github.com/Eldinnie/a94f313eb74d7d1ef8579a514f18f1a4 If you send /start -> /brew it will timeout (which will set the state to END) but after 20 seconds it will still send the message from brew

I also think timed_out_behavior is badly named. From the name I would expect whatever is in there to happen when it's timedout (especially with the conversation_timeout also an argument)

Question:
Why was run_async_timeout and timed_out_behavior added, and mostly do we still need it with the new mechanics?
Is it possible to stop a promise from running if timeout is reached?

Proposal.
Remove run_async_timeout and timed_out_behavior kwargs and functionality. I think it's superseeded with the newer timeout mechanics.