How to add a custom agent harness?

[ferrreo]

Is there a way to add a custom internal agent harness when self hosting without pretending to be one of the others or forking the project? ACP or something?

[cookesan]

Not as a config-only hook in the current source.

There is a clean internal agent.Backend interface, but provider selection is a fixed registry/switch over known agent types such as Claude, Codex, Gemini, OpenCode/OpenClaw, Hermes, Kimi, Cursor, etc. The model listing and launch headers are also keyed off that fixed provider set. custom_args, environment, and MCP config can adapt a supported harness, but they do not add a new agent type.

ACP can be the protocol a backend uses, and some built-in providers already use ACP-style labels, but it is not dynamic provider loading by itself here. To add a real internal harness without pretending to be another provider, upstream would need a plugin/provider registration surface, or you would add a backend implementation and register it in agent.New, model listing, launch metadata, runtime detection, and the UI/provider selection path.