muse-go: Muse Code on OpenCode Go and Zen

# muse-go

Run the **Muse Code harness** against either OpenCode route without changing normal Muse configuration:

```text
muse-go  -> https://opencode.ai/zen/go/v1/responses -> muse-spark-1.3-contributor
muse-zen -> https://opencode.ai/zen/v1/responses    -> muse-spark-1.3-contributor-free
```

No proxy is needed. OpenCode documents both as Responses API models, and the current Muse request/stream/tool protocol works directly. The Zen variant is currently free for a limited time; the Go variant belongs to the Go subscription.

> **Contributor privacy warning:** this discounted model explicitly permits Meta to use prompts and completions to train future models. OpenCode's privacy table marks it as **training: yes** and **not ZDR** (not zero-data-retention). Do not send private source, credentials, personal data, or other content unsuitable for that use.

## Requirements and setup

- `muse` (validated with Muse Code 1.0.1 and 1.0.2)
- `python3`
- an OpenCode API key; a Go subscription is needed only for `muse-go`, not the currently free Zen route
- `curl` for diagnostics
- optionally `opencode` for its credential store and model metadata

```bash
./setup.sh       # Go profile
./setup-zen.sh   # free Zen profile

./muse-go exec 'inspect this repository'
./muse-zen exec --json 'reply with exactly OK'
```

The recommended credential setup is `opencode auth login`. The launchers read OpenCode's documented local auth file (`~/.local/share/opencode/auth.json`):

- `muse-go` uses the `opencode-go` entry.
- `muse-zen` prefers the `opencode` entry, then falls back to `opencode-go`.

Live tests found asymmetric scope: either local key works on Zen, but this machine's Zen (`opencode`) key was rejected by Go while its `opencode-go` key works on both. Therefore **one Go key is sufficient for both commands**, but a Zen-only key is not necessarily sufficient for Go. The two stored key strings on this machine are distinct. Environment overrides remain available: `OPENCODE_GO_API_KEY` for Go, `OPENCODE_ZEN_API_KEY` for Zen, or generic `OPENCODE_API_KEY` for either. Override the store path with `OPENCODE_AUTH_FILE`.

The launcher maps the key to `META_API_KEY` **only in the child Muse process**, because Muse currently names its sole network model provider `meta`. It never puts the key in command arguments or copies it into this repository/Muse auth storage. Environment variab