Plugin Package Guide

The server SDK has two versions: Effect and Promise. src/tui/ is the TUI SDK and src/gui/ the GUI SDK.
In the Effect version, every domain must extend the corresponding Effect API client interface from @opencode/client/effect/api.
Do not redefine functions that already exist on the Effect API client interface.
Plugin domains add only the additional functions that make sense in the plugin context.
The GUI SDK never loads in the server or the TUI, so runtime-modules.ts skips gui/ and the CLI bundle does not grow.
src/gui/ follows packages/gui-plugins/AGENTS.md: the built-ins there are its main users, and bun run lint from the repository root checks its TSDoc (script/sdk-docs.ts). Run bun run generate here after the app's icon catalog changes.
src/gui/host.ts (@opencode/plugin/gui/host) is the app's and desktop's internal protocol, for workspace imports only: tsconfig.build.json leaves it out of dist and script/pack.ts exports it as null. Keep public SDK modules from importing it.
src/gui/builtin.ts (@opencode/plugin/gui/builtin, the API only the app's built-in plugins use) and src/gui/updater.ts (@opencode/plugin/gui/updater, the app's own updater contract) are workspace-only the same way, and neither is a module a plugin bundle may require. src/gui/internal.ts holds the window host's internals the public helpers read; gui/host re-exports them. The ./gui/* export is null, so only the listed gui subpaths resolve.