Pattern: The Control Stack — Rules, Skills, Bounded Subagents, Deterministic Tools — Has Displaced Prompt Engineering

Developers Digest·medium signal

The consensus pattern emerging across practitioner writing in July 2026 is a four-layer control stack around the model: project rules, reusable skills, bounded sub-agents, and deterministic tools, with human checkpoints between stages. The claim is that decomposition into bounded subtasks beats one long agent run not because the model is weak but because bounded scopes are verifiable. rtk and lean-ctx fit the "deterministic tools" layer; skills fit the reuse layer — the stack is now buildable off the shelf.