# Step 11 — Capstone: watch your kernel run

No test to make green here. This is the payoff. `game.js` contains the **exact
engine you built** across steps 01–10 — the same `sweptAABB`, `slide`, and
`moveAndSlide`, assembled into one file — wired to a canvas and the arrow keys.

## Run it

It's a plain HTML file with no build step. Any of these work:

```sh
# simplest: just open the file in a browser
xdg-open workshop/steps/11-capstone/index.html      # linux
# or drag index.html into a browser window

# or serve it (nicer, avoids any file:// quirks):
bunx serve workshop/steps/11-capstone
# then open the printed http://localhost:... URL
```

Arrow keys move the pink box. Run it into the border, the ledge, the pillar, the
bar. Push diagonally into a wall and watch it **slide** along instead of
sticking. That sliding is your step-09 `dot`-product projection. The fact that
it stops _at_ the wall instead of tunneling through, even at speed, is your
step-07 swept detection. The clean corners are your step-10 loop running twice
in one frame.

## Make it yours (optional)

- Open `game.js`. The top half is your kernel — read it and confirm it matches
  what you wrote. Swap in your own `moveAndSlide` from step 10 and check it
  feels identical (it will).
- Add a wall to the `walls` array. Change `SPEED`. Make the player bigger.
- Try **deleting the `EPSILON` backoff** (`Math.max(0, nearest.time - EPSILON)`
  → `nearest.time`) and push into a wall. Watch it stick and jitter. Then put it
  back. Now you've _felt_ why that line exists in your real engine.

## You're back

That's the whole climb: pairs of numbers → sweeping a point → sweeping a box via
Minkowski → detecting the hit → stopping and sliding → the full loop → a thing
you can play. Every rung is a function that exists, by name, inside your real
`engine/system/physics.ts`.

Now go open the real `sweptAABB` with fresh eyes. You know exactly what every
line is _supposed_ to do — so the two lines that don't should stand out. Happy
hunting.