Why this is the leash for an agent
A boundary is not just structure. It is the smallest unit you can safely delegate.
Now the agent-era payoff. A bounded core behind a port is the smallest unit you can safely hand to an agent. “Implement InviteTeammateHandler so that it satisfies this port and enforces these rules” is a task an agent cannot sprawl out of — the boundary is the leash. It can’t wander into your database schema or your HTTP layer, because the port stands between it and them. And because the unit is small and bounded, you can actually verify what it gives back.
This is the seed to remember, because we harvest it twice later in the course: a boundary is a unit of delegation. The same edge you draw for human comprehension is the edge you hand to an agent. Draw your boundaries well and you’ve simultaneously made the system understandable, testable, and delegable. Draw them badly and no amount of agent horsepower will save you — it’ll just generate the mess faster.