That's right each harness runs in it's own sandbox. Really the harness itself is just a docker template with some pre-installed harness (say openclaw, hermes, claude code, opencode, pi, grok etc) that runs.

For convenience and cross-harness unified API we also built open source Gateway API - https://github.com/agent37-platform/gateway

Think of it as open router for Agent harnesses. So in our default templates we also run this and expose the APIs. So that makes using any harness easy as they all speak a single OpenAI responses API schema.