new-harness

name	new-harness
description	Scaffold a new agent harness for open-managed-agents and register it. Use when adding a new way to drive the model loop, like the default / acp-proxy / flue harnesses.
disable-model-invocation	true

Scaffold a new harness named $ARGUMENTS (the string an agent selects via harness: "<name>").

1. Read the current contract first — open apps/agent/src/harness/interface.ts and use the live HarnessInterface, HarnessContext, and HarnessRuntime shapes. Do NOT assume a signature from memory; the interface evolves.

2. Study a real implementation for the pattern:

   • apps/agent/src/harness/default-loop.ts (DefaultHarness) — drives its own streamText/generateText loop.
   • apps/agent/src/harness/acp-proxy-loop.ts / flue-loop.ts — meta-harnesses that hand the turn to an external runtime and make shouldCompact / compact / deriveModelContext deliberate no-ops.

3. Create apps/agent/src/harness/<name>-loop.ts exporting a class that implements HarnessInterface. run(ctx) is required; only override the optional hooks (onSessionInit, shouldCompact, compact, deriveModelContext) where this harness must diverge from platform defaults. If you override deriveModelContext, keep its output byte-deterministic — the prompt cache invalidates on any prefix drift (see the interface comments).

4. Register it in apps/agent/src/index.ts, next to the existing registerHarness(...) calls:

   import { <Name>Harness } from "./harness/<name>-loop";
   registerHarness("<name>", () => new <Name>Harness());
   

5. Add a unit test alongside the existing harness tests, then run /preflight.