add-opencode

# OpenCode agent provider Install OpenCode as an optional NanoClaw runtime. The payload is included in this skill; it needs no separate provider branch. It uses the upstream runtime, instructions, host, and setup metadata contracts. The host contract remains at version 1; the container owns its non-secret ChatGPT placeholder file. OpenCode is offered by the standard setup provider picker. Existing installs can add or authenticate it with `pnpm exec tsx setup/index.ts --step provider-auth opencode`. To replace an installed payload and update its pins, append `--refresh`; back up local payload edits first. Ordinary re-authentication leaves installed files and the container image alone. Backend defaults are installation-wide; model and reasoning effort can be overridden per group through the existing container configuration. Per-group backend/auth selection and structured channel attachment transport are separate work. Authentication checks the installed files, registration lines, and exact pins against this skill's declarations without launching a subprocess or container. Install and refresh run the existing provider contract verification; the build step owns image freshness. Model selection does not repeat installation checks. A working backend and account are checked separately by sending a real request. ## Install After installing this payload, run `pnpm exec tsx scripts/opencode-host.ts --configure` for host OpenCode setup, or use `--update` / `--debug` for the corresp...