Comment by agentultra

That's an important question to ask!

Can you assume the reactor has durable, local storage with atomic transactions?

The answer is to model your design and use a sufficient level of rigour in validating that your system meets your requirements.

Maybe you could use a database server that has the right properties to ensure your reactor could survive a restart.

What if you want to add multiple reactors so that you can process an event stream with a high volume of events, faster?