meta-harness means two things: Databricks' control plane and Stanford's outer-loop optimizer. This post uses a four-layer model (MCP/ACP/Runtime/meta-harness) to place Omnigent, Zed ACP, Vercel HarnessAgent and Cloudflare Flue.
Five external CLIs expose five different machine interfaces: JSONL event streams, JSON-RPC handshake, HTTP API, ACP, stream-json. The right way to support them is not one interface that pretends they're identical — it's a narrow runtime boundary plus an honest capability matrix. Availability means installed, not authenticated; protocol drift fails closed.