How to build your own agent harness???
iii proposes an alternative to monolithic agent frameworks: decomposing the harness into a set of independent workers on a shared WebSocket engine. Each of the 15 responsibilities (turn orchestration, auth, policy, approval, session, etc.) is a separate worker that registers functions and triggers on a common bus via iii.trigger(). The architecture makes every layer replaceable—swap the model catalogue by writing a worker that registers models::list, add a provider with provider::<name>::stream, without touching the rest of the stack. The post walks through the turn loop in detail, explaining how provisioning, streaming, tool execution, approval gating, and teardown work across workers. Concrete replacement examples include model catalogue, credential store, approval UI, and policy engine. The entire harness is open source (github.com/iii-hq/workers), with all workers operating under the same protocol, yielding full OpenTelemetry tracing. The key insight: 'build your own harness' means swapping workers, not forking a framework, enabling a slider between thin and thick setups.