Why it matters

Subagents are the answer to the context wall from Chapter 4 and the path to parallel throughput from Chapter 8. They are also how you encode specialization (a security reviewer, a test runner, a verifier) and how you keep noisy work from poisoning the main thread. Most importantly, the verifier pattern is a structural reliability mechanism: independent checking is how you catch an agent that confidently shipped something broken, which is the central risk Chapters 13 and 16 are about.