Availability data refreshed from server on every calendar view load

Serving stale availability data is a direct cause of double-bookings. When a customer books slot A, that change must be visible to every other client on the next calendar load — not after a session refresh or browser restart. Client-side caches without TTLs violate CWE-362 (concurrent resource access) and ISO 25010 functional correctness: two users see the same slot as open and both confirm. The downstream effect is a support ticket, a refund, and a damaged reputation. Booking platforms live and die by schedule integrity; a single double-booking erodes trust faster than any competitor can.

Add month and year (or equivalent time-period identifiers) to the useEffect dependency array in your calendar component so a fresh fetch fires on every navigation, not just on mount. Include a cache-buster parameter or set Cache-Control: no-cache on the server endpoint.

useEffect(() => {
  fetch(`/api/availability?month=${month}&year=${year}&t=${Date.now()}`)
    .then(r => r.json())
    .then(setSlots)
}, [month, year]) // re-runs on every period change

On the API route in src/app/api/availability/route.ts, set the response header:

return new Response(JSON.stringify(slots), {
  headers: { 'Cache-Control': 'no-cache, no-store, must-revalidate' },
})