Welcome back to the Harness Engineering series — a 10-part journey from raw language model to production-ready agentic system. Made by builders. For builders.
In Part 5, we looked at the Context — the payload the model sees on every call. Now we look at what happens after the model, having seen that Context, decides to do something.
The model calls a tool. The tool has to execute somewhere. That somewhere is the Environment.
It's easy to under-appreciate. The Environment feels like plumbing — the filesystem, the shell, the network, the machine underneath. But it's where every side effect the model requests actually lands, and how you design it is what separates "an AI agent doing things on your behalf" from scary to routine.
What's ahead:
