Add NOTES.md

Write-up of the plan, model choice, commit split, and what the
self-review found for the update-user endpoint.

Author: FelipeDeYcaza

NOTES.md

@@ -0,0 +1,35 @@
+# NOTES
+
+## Plan
+
+The approved plan added a `PUT /users/:id` route in `routes/users.js` and a matching
+`updateUser(id, { name, email })` helper in `db/store.js`, both mirroring the existing
+`GET /:id` and `POST /` handlers (same 404 shape, same "name and email are required" 400
+message). The plan specified validating input before doing the lookup, so a request with
+a missing field 400s even against a real id — that matched how the tests exercise each
+case independently, and I approved it as written without edits.
+
+## Model
+
+Used Claude Sonnet 5 for the whole task — plan, implementation, and review. The change is
+small and follows patterns already present in the codebase, so there was no need for a
+larger/slower model; Sonnet handled the plan-mode exploration and the route/store code
+without any back-and-forth.
+
+## Commits
+
+Split into three: `db/store.js` (the `updateUser` helper) first, then `routes/users.js`
+(the route that uses it), then this `NOTES.md` last. Store-then-route mirrors the
+dependency between them (the route can't be written meaningfully without the helper it
+calls), and keeping `NOTES.md` as its own commit means the write-up can honestly describe
+what actually happened during implementation and review rather than what was planned.
+
+## Review
+
+Ran a self-review (correctness, removed-behavior, cross-file, reuse/simplification/
+efficiency, altitude, conventions) against the two-file diff before pushing. Nothing came
+back: validation runs before the store lookup as planned, `Number(req.params.id)` on a
+non-numeric id degrades to `NaN`/not-found the same way the existing `GET /:id` handler
+already does, and the new store helper mutates the existing user record in place rather
+than duplicating any lookup logic. The review confirmed the implementation was clean
+rather than catching anything that needed fixing.