Cursor 3 vs DOOM MCP

Cursor 3 launched on April 2, 2026 with the biggest architectural shift since the team forked VS Code. The new Agents Window lets developers run multiple AI agents in parallel — each in its own isolated VM on a separate Git branch — while you stay in the editor reviewing their work. Background agents handle full feature implementations, batches of bug fixes, or multi-file refactors without blocking your current session. The release also introduces Design Mode, which lets developers click any UI element and describe changes in plain English — the agent handles the implementation. Composer 2, Cursor's in-house model trained specifically on code editing, ships alongside it with tighter context handling and fewer hallucinated diffs. Cloud agent handoff, multi-repo layout, and seamless local/remote context switching round out the release. The deeper shift is philosophical: Cursor is no longer positioning itself as a smart code editor — it's an agent orchestration platform that happens to include an IDE. The interface now treats the developer as a director, not a typist. Cursor 3 demotes the editor window to a fallback for review; agents are the primary execution surface.

Chris Nager built a fully playable DOOM that runs as an MCP (Model Context Protocol) app, rendering inline inside Claude and ChatGPT without a separate browser tab. The architecture uses two MCP tools — create_doom_session for inline-capable hosts and get_doom_launch_url as a browser fallback — combined with cloudflare/doom-wasm for the game runtime and a signed token system that maintains session state across both surfaces. The result is the same session whether you're playing inline or in a tab. The key technical challenge was avoiding iframe and CSP (Content Security Policy) issues. Rather than embedding a browser page inside the MCP iframe, the DOOM canvas runs directly inside the host's iframe — a subtle but critical distinction that resolved a class of rendering and input-handling bugs. The final implementation is intentionally stripped down: no save/load, no persistence adapters, just stable playable DOOM. Beyond the novelty, this project is a concrete demonstration that MCP apps are interactive surfaces, not just tool-calling JSON endpoints. The progressive enhancement pattern — same signed-token foundation serving both inline and browser modes — is a reusable architecture for any game or interactive experience that wants to live inside an AI assistant. Nager open-sourced the implementation and the blog post is a detailed technical breakdown.