Why it matters

Parallelism is a direct speed win: independent reads finish in the time of the slowest one instead of the sum. The API and protocol material matters less for a hobby agent and more the moment you want to (a) control costs (use an agent-friendly API and protect caching), or (b) build anything beyond a single CLI session. If you ever want an orchestrator coordinating several agents, or an IDE plugin, you are building on something App-Server-shaped, and the items/turns/threads model is the right vocabulary to reach for.