Add PUT /users/:id update endpoint

NOTES.md

@@ -0,0 +1,17 @@
+# Notes
+
+## Plan
+
+The plan was to add `updateUser(id, { name, email })` to `db/store.js` following the same pattern as `createUser`, then wire up a `PUT /users/:id` route in `routes/users.js` following the same shape as the existing GET and POST routes. The plan needed no edits — the test file made the requirements explicit (200 on success, 404 for unknown id, 400 for missing fields).
+
+## Model choice
+
+Claude Sonnet 4.6. The task is straightforward CRUD with clear tests, so the fastest capable model was the right call — no need for extended reasoning.
+
+## Commit split
+
+Two commits: one for the store helper (`updateUser`) and one for the route (`PUT /users/:id`). Each commit is independently understandable and the store change is useful even without the route.
+
+## What the review caught
+
+The review confirmed the implementation was correct: validation runs before the store lookup (so a 400 is returned before attempting an update), and `updateUser` returns `null` on a miss so the route can return 404 cleanly. No issues found.

db/store.js

@@ -24,4 +24,12 @@ function createUser({ name, email }) {
   return user;
 }
 
-module.exports = { getAllUsers, getUserById, createUser };
+function updateUser(id, { name, email }) {
+  const user = users.find((u) => u.id === id);
+  if (!user) return null;
+  user.name = name;
+  user.email = email;
+  return user;
+}
+
+module.exports = { getAllUsers, getUserById, createUser, updateUser };

routes/users.js

@@ -20,6 +20,24 @@ router.get("/:id", (req, res) => {
   res.json(user);
 });
 
+// PUT /users/:id — update a user; name and email are required; 404 if not found
+router.put("/:id", (req, res) => {
+  const { name, email } = req.body;
+
+  if (!name || !email) {
+    return res.status(400).json({ error: "name and email are required" });
+  }
+
+  const id = Number(req.params.id);
+  const user = store.updateUser(id, { name, email });
+
+  if (!user) {
+    return res.status(404).json({ error: "User not found" });
+  }
+
+  res.json(user);
+});
+
 // POST /users — create a user; name and email are required
 router.post("/", (req, res) => {
   const { name, email } = req.body;