@metaharness/host-opencode

OpenCode (sst/opencode) host adapter for agent-harness-generator. The 8th host adapter, per ADR-036.

What it does

Generates the config files a harness needs to run inside OpenCode, the open-source terminal AI coding agent by SST.

Emits per adapter.generateConfig(spec):

• .opencode/opencode.json — the OpenCode 1.x project-scoped config: $schema anchor, mcp.servers registration table, mcp.permissions allow/deny block
• install.md — runbook for opencode auth login, model-provider selection, and the first-boot smoke

Schema (OpenCode 1.x)

{
  "$schema": "https://opencode.ai/schema/opencode.json",
  "mcp": {
    "servers": {
      "codeindex": {
        "command": "node",
        "args": ["./dist/mcp-server.js"],
        "env": { "LOG_LEVEL": "info" }
      },
      "remote": {
        "url": "https://example.com/mcp"
      }
    },
    "permissions": {
      "allow": ["mcp__codeindex__*"],
      "deny": ["Bash(rm:*)", "Bash(git push:*)"]
    }
  }
}

Default-deny composition

OpenCode evaluates mcp.permissions.deny before allow. This adapter copies the harness's .harness/mcp-policy.json deny rules verbatim, so the default-deny posture from ADR-022 wins through OpenCode's own enforcement gate — no second source of truth.

Constraints

• OpenCode 1.0+ — earlier 0.x versions had a different config layout
• A model provider configured (opencode auth login)
• .opencode/opencode.json is re-read on :reload, not hot-edit

Programmatic use

This adapter is normally consumed via npx metaharness <name> --host opencode. Direct programmatic use:

import { adapter } from '@metaharness/host-opencode';
const files = adapter.generateConfig!(harnessSpec);
// files === { '.opencode/opencode.json': '...', 'install.md': '...' }

License

MIT — see LICENSE.