Add check_opencode_plugins() to read ~/.config/opencode/opencode.json, parse the plugin[] array, and cross-reference against ~/.cache/opencode/node_modules/ to report installed vs. missing plugins. Also adds opencode_config_path, opencode_cache_dir, and has_project_opencode_config helpers. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>