# Switch harness mid-feature
> Relay a feature's session from one harness to another with the same branch and worktrees, and nothing uploaded.
Source: https://ivar.run/docs/recipes/switch-harness

You need a hall with at least two providers and a feature with a session. This example moves `avatar-url` to OpenCode. If the hall lacks the provider, `ivar provider add opencode` registers it.

```sh
ivar session relay avatar-url --provider opencode
```

`--provider` is required, because a relay exists to switch harnesses.

## What happens

- The worktrees are git, the manifest is JSON and the skills are folders of Markdown, so nothing in the view dir belongs to one vendor.
- The feature keeps its branch and its promoted repos. Only the harness that reads them changes.
- The new session gets the new provider's native files: `.opencode/` and `AGENTS.md` in this example.
- Nothing is uploaded to do it.
- To open a fresh session on the same feature under the new provider, use `ivar session start avatar-url --provider opencode`.

Use it when one harness hits a limit you do not want to wait out, or when a teammate prefers another one. Check the result with `ivar feature status avatar-url`: the promoted repos and their states match what you left. Run `ivar session stop` on the old session when you finish with it, so a second agent never writes into the same worktrees.

The relay prints four lines of output for external consumers, so a script or an editor can read the new session's binding. Add `--json` for the same value in machine-readable form. The hall's `ivar.json` lists which providers are available, and `ivar provider list` shows them with the default.

Instruction files follow the provider. The hall's `HALL.md` becomes `CLAUDE.md` for Claude Code and `AGENTS.md` for OpenCode and OMP, so the new agent starts with the same rules the old one had, and the skills are the same Markdown folders under a different harness directory.

## Read the full walkthrough

The [session reference](/docs/reference/session#relay-to-another-harness) covers relay and the binding variables a session exposes. [With OpenCode](/docs/with/opencode), [with Claude Code](/docs/with/claude-code) and [with OMP](/docs/with/omp) show what each harness gets.