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.