time for a snapshot

workshop/steps/11-capstone/README.md

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+# 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.