Parametric CAD models that explain how mechanical power flows through real machines, built entirely with open-source tools and rendered live in a static three.js viewer that ships to GitHub Pages.

Two models live here today:

• build123d — Python parametric CAD, generates the assembly as a labeled Compound of solids.
• CAD Skills (earthtojake/text-to-cad) — agent-skill toolkit that handles STEP generation, GLB/topology export, and CAD Explorer rendering.
• .<name>.step.js sidecar — a tiny ES module per model that exports a manifest (parameter definitions + occurrence-id features) and an update(ctx) function that drives part transforms from the live parameters. The same sidecar runs inside the CAD Explorer locally and in the static Pages viewer.
• site/ — a hand-rolled three.js viewer (~500 LOC) that loads the GLB, reparents each top-level o1.N occurrence into a wrapper group, and runs the sidecar's update() every frame to apply matrices and colors.

models/
  f1_car/
    f1_car.py          # build123d generator
    f1_car.step        # exported STEP (one solid compound)
    .f1_car.step.glb   # mesh + STEP_topology extension
    .f1_car.step.js    # animation sidecar
    renders/           # PNG / GIF previews used as thumbnails
  bicycle/
    bicycle.py
    bicycle.step
    .bicycle.step.glb
    .bicycle.step.js
    renders/

site/
  index.html           # landing page (model cards)
  viewer.html          # generic ?model=... viewer page
  viewer.js            # three.js + STEP-module sidecar runner
  style.css
  build-models.sh      # copies models/ -> site/models/ for deployment

.agents/skills/        # CAD Skills installed via `npx skills add`

source .venv/bin/activate
python .agents/skills/cad/scripts/step models/bicycle/bicycle.py

This rewrites bicycle.step, the hidden .bicycle.step.glb, and assorted topology sidecars. Open it locally with:

npm --prefix .agents/skills/render/scripts/viewer run dev:ensure -- \
  --workspace-root "$PWD" --file models/bicycle/bicycle.step

1. Drop a new <name>.py in models/<name>/ that exposes a gen_step() returning a labeled Compound.
2. Generate models/<name>/<name>.step with the launcher above.
3. Write models/<name>/.<name>.step.js (ES module exporting { manifest, update(ctx) }). Reference parts by #o1.N selectors in manifest.features.
4. Render a hero PNG (models/<name>/renders/hero.png) so the landing card has a thumbnail.
5. Register the model in site/viewer.js MODELS = { ... }.
6. Add a card to site/index.html.

A GitHub Actions workflow (.github/workflows/pages.yml) bundles site/ + the necessary files from models/ and publishes them to Pages on every push to main. After the first run, enable Pages in the repository Settings → Pages → Build and deployment → GitHub Actions.