Create OpenCode plugins using @opencode-ai/plugin SDK. Use when user wants to BUILD a plugin in .opencode/plugin/ or ~/.config/opencode/plugin/ - for custom tools, event hooks, LLM parameter control, auth providers, or tool execution interception. DO NOT use when modifying OpenCode source code (packages/plugin, packages/opencode, etc.) or working on OC internals - those are core development, not plugin creation.