Cursor-style Coding App

August 17, 2026 · View on GitHub

The primary application for the Build a Cursor in 3 Steps HarnessRouter workshop at Harvard.

This demo shows how to turn a purpose-configured HarnessRouter coding agent into a product experience with streamed output, recoverable sessions, follow-up tasks, cancellation, and artifact downloads.

Run it

From the repository root:

Install dependencies.
```
npm install
```
Copy .env.example to the repository root as .env, then set both values.
```
HR_API_KEY=your_key_here
HR_CURSOR_AGENT_ID=your_coding_agent_id
PORT=3000
```
No key yet? Create one from the quickstart. Starting the demo consumes no credits; credits are only used when tasks run.
Start the primary demo.
```
npm run dev:cursor
```

Open http://localhost:3000.

Architecture

Layer	Responsibility
`config/agents.json`	Declares the `coding_assistant` feature; `HR_CURSOR_AGENT_ID` supplies its HarnessRouter agent ID
`server/index.ts`	Keeps credentials server-side and proxies runs, sessions, cancellation, previews, and downloads
`src/api.ts`	Parses data-only server-sent events
`src/App.tsx`	Provides the Cursor-style coding-agent interface and session history
`tests/`	Covers stream parsing and cross-user session ownership

The demo intentionally does not include a production repository sandbox. Configure the HarnessRouter coding agent with the tools and repository access appropriate to your environment.

Direct workspace commands

npm run test --workspace=@harnessrouter/cursor-coding-app
npm run build --workspace=@harnessrouter/cursor-coding-app
npm run preview:cursor