time for a snapshot

workshop/steps/01-vectors/README.md

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+# Step 01 — Vectors
+
+> You know this cold. The point of this step is to make the red→green loop
+> automatic, not to teach you arithmetic. Blast through it.
+
+## Concept
+
+A **vector** here is nothing mystical: a pair of numbers `(x, y)`. We use the
+same value to mean two different things depending on context:
+
+- a **position** — a point in the world.
+- a **displacement / velocity** — an arrow: "move this much in x, this much in y."
+
+That's it. All of 2D physics is built on adding, subtracting, and scaling these
+pairs.
+
+- `add(a, b)` → `(a.x + b.x, a.y + b.y)` — apply an arrow to a point.
+- `sub(a, b)` → `(a.x - b.x, a.y - b.y)` — the arrow that points *from b to a*.
+- `scale(a, s)` → `(a.x * s, a.y * s)` — make an arrow longer/shorter.
+
+> Note: we return **new** objects (pure functions) here for clarity. Your real
+> engine mutates vectors in place to avoid garbage collection — that's a speed
+> optimization we'll deliberately ignore until the very end.
+
+## Task
+
+Implement `vec`, `add`, `sub`, and `scale` in `vector.ts`.
+
+```sh
+bun test workshop/steps/01-vectors
+```