[appkit plugin] [7/x] Add default-ui playground for @databricks/appkit-agent

[hubertzub-db]

🥞 Stacked PR

• stack/agent-plugin-p2
• stack/agent-plugin-p3 (diff)
• stack/agent-plugin-p4 (diff)
• stack/agent-plugin-p5 (diff)
• stack/agent-plugin-p6 (diff)
• stack/agent-plugin-p7 (diff)
• stack/agent-plugin-p8 (diff)

---

Summary

Adds a minimal playground app (integrations/appkit-agent/playground/default-ui/) that demonstrates the agent + chat plugin stack with the bundled UI from p6. The playground is a server-only project — it imports @databricks/appkit-agent as a workspace dependency and uses chat.staticAssetsPath to serve the pre-built chat client.

This serves as a development testbed and a reference example for wiring the plugins together.

Playground setup

playground/default-ui/
  server/index.ts    # ~18 lines — the entire app
  package.json
  .env.example
  tsconfig.json

server/index.ts is the complete application:

import { createApp, server } from "@databricks/appkit";
import { agent, chat } from "@databricks/appkit-agent";

await createApp({
  plugins: [
    server({ autoStart: true, staticPath: chat.staticAssetsPath }),
    agent({
      model: process.env.DATABRICKS_MODEL || "databricks-claude-sonnet-4-5",
      systemPrompt: "You are a helpful assistant.",
      tools: [],
    }),
    chat({
      backend: "agent",
    }),
  ],
});

How to run

cd integrations/appkit-agent/playground/default-ui
cp .env.example .env
# Configure DATABRICKS_CONFIG_PROFILE or DATABRICKS_HOST + DATABRICKS_TOKEN
pnpm install
pnpm run dev   # tsx watch --env-file=.env server/index.ts

Other changes

• .gitignore: added .env and .env.local to prevent committing secrets
• src/chat-plugin/types.ts: duplicate autoMigrate field added during rebase (to be cleaned up)