Here is an interesting find.

Let's say that you have two agents running concurrently: A & B. Agent A decides to push a message into the context of agent B. It does that and the message ends up somewhere in the list of the message right at the bottom of the conversation.

The question is, will agent B register that a new message was inserted and will it act on it?

If you do this experiment you will find out that this architecture does not work very well. New messages that are recent but not the latest have little effect for interactive session. In other words, Agent A will not respond and say, "and btw, this and that happened" unless perhaps instructed very rigidly or perhaps if there is some other instrumentation in place.

Your mileage may vary depending on the model.

A better architecture is pull-based. In other words, the agent has tools to query any pending messages. That way whatever needs to be communicated is immediately visible as those are right at the bottom of the context so agents can pay attention to them.

An agent in that case slightly more rigid in a sense that the loop needs to orchestrate and surface information and there is certainly not one-size-fits-all solution here.

I hope this helps. We've learned this the hard way.

Yep, I didn't want to have to think about concurrency so my solution was a global lock file on my VM that gets checked by a pre-start hook in claude code. Each of my "agents" is a it's own linux user with their own CLAUDE.md, and there is a changelog file that gets injected into that each time they launch. They can update the changelog themselves, and one agent in particular runs more frequently to give updates to all of them. Most of it is just initiated by cron jobs. This doesn't scale infinitely, but if you stick to two-pizza teams per VM it will still be able to do a lot.

So hooks are your friends. I also use one as a pre flight status check so it doesn't waste time spinning forever when the API has issues.