Brian's piece "agents need control flow, not more prompts" hit the HN front page today with 300+ points, and the core argument is right: prompting is not a programming language. Reliable agents need deterministic scaffolding, explicit state transitions, validation checkpoints. The LLM becomes a component inside a system that controls it, not a system that controls itself through sheer prompting willpower. One commenter framed it perfectly: "use the non-deterministic thing that is right 90% of the time to generate a deterministic thing that is right 100% of the time." That's correct. And it leaves a gap open. Control flow is the agent's internal view When you add control flow to an agent (explicit branching, validation gates, retry logic, typed I/O), you create a scaffold that constrains what the agent can do. The LLM still decides. The scaffold ensures those decisions run through the right checks.…