Capstone: A Complete, Working Food Tracker

Marcus scans a carton of milk. Chapter 4's useBarcodeScanner hook decodes the barcode entirely client-side, then handleDetected calls fetch("/api/lookup/...") — Chapter 3's route, which checks barcode_cache first and falls back to a live Open Food Facts call, caching whatever it finds.

Chapter 5's AddItemForm pre-fills the name and category from that lookup. Marcus sets the expiry date and submits; the client-side check catches an empty name instantly, but it's Chapter 3's own POST /api/items route — the real gate, by construction — that actually validates and inserts the row, exactly as Chapter 5's finding-box promised it would.

Chapter 6's alerts route surfaces the milk once it's within three days of its (consistently YYYY-MM-DD-formatted) expiry date — a plain SQL range query needing no index at all, at this app's own realistic scale.

Wanting to check if he's bought a particular brand of yogurt before, Marcus types "yog" into the search box. Chapter 7's useDebouncedSearch waits for him to stop typing, then hits the search route's native, case-insensitive LIKE match — no shadow field required, unlike the Firebase sibling's own nameLower.

The milk gets finished. Chapter 8's PATCH /api/items/:id/use — never a plain link — sets status='used', stamps used_at, and clears expiry_date to NULL, guarded by AND status = 'active' so accidentally clicking twice changes nothing the second time.

Marking the milk used calls Chapter 10's notifyChange() — one call, with no knowledge of who's listening. The alerts dashboard disappears the milk from its own list; the recipe suggestions (Chapter 9) stop counting it as an expiring ingredient — both react on their own, independently, exactly as Chapter 10's whole redesign was built to make possible.

With chicken and spinach both nearing expiry, Chapter 9's Promise.all fan-out queries TheMealDB for both concurrently — not sequentially, a real, honest advantage over the Django sibling's own admitted sequential cost — merging and sorting the results by how many expiring ingredients each recipe actually uses.

Marcus's session happens against a real deployment: Express serving the built React app via Chapter 11's own catch-all SPA route (registered after the API routes, never before), pm2 keeping the process alive, nginx terminating HTTPS in front of it, and the SQLite file sitting on a volume that survives a redeploy.