VPython for VS Code notebooks

Renders VPython 3D scenes in VS Code's notebook UI. Companion to vpython-jupyter's websocket-only frontend (with_wsfrontend.py, branch feat/vscode-frontend): under VS Code the kernel skips the classic Comm/nbextension machinery, serves the whole VPython wire protocol on a tornado websocket inside the kernel, and announces it with an application/vnd.vpython.v1+json output. This extension's renderer picks that up, loads GlowScript (bundled jquery + glow.min), connects to the websocket, and drives glowcomm_host.js — the same host-agnostic protocol frontend the trinket worker integration uses.

kernel (python)                          VS Code output webview
─────────────────                        ──────────────────────
with_wsfrontend.py                       renderer.js
  tornado ws server  ◄──── ws ────►        glowcomm_host frontend
  WsSender (buffers)   duplex              glow.min.js (GlowScript)
  display(MIME{port})  ────────────►       (this is how the port arrives)

• downlink: kernel sender(package) → ws → fe.handle(package)
• uplink: 33 ms pacer → fe.tick() → events (or update_canvas trigger) → ws → kernel ws_queue → handle_msg → trigger() flushes updates
• v1 assumes kernel and UI share a machine (127.0.0.1); remote kernels need asExternalUri port forwarding via the extension host — future work.

1. Kernel env: install the branch — VPYTHON_PURE_PYTHON=1 pip install -e <vpython-jupyter checkout on feat/vscode-frontend>
2. Install the extension vsix: code --install-extension vscode-vpython-0.1.0.vsix, then Developer: Reload Window.
3. Open test-workspace/vpython-demo.ipynb, pick that kernel, run the cells.

VPYTHON_FRONTEND=ws forces the websocket frontend outside VS Code; VPYTHON_FRONTEND=jupyter forces classic behavior under VS Code.

• Fonts for text() objects not bundled yet (glow loads them from the host)
• Widgets (button/slider/menu) and scene.pause/waitfor: same deferrals as the trinket worker integration — glowcomm_host warns and drops
• Remote/WSL/Codespaces kernels (port forwarding)
• One scene container per MIME output; every canvas() renders into the import cell's output

Learned in the spike (../vscode-vpython-spike): never assign innerHTML (Trusted Types rejects it and kills the render silently); build DOM with createElement/textContent; render every failure into the output element so nothing fails invisibly; ship a text/plain fallback beside the MIME.