Next.js Silent Failures

The failure these share

Nothing here crashes. The page renders, the build is green, and the build output reads as a performance win — while the data is stale, or private, or decided by a user-agent string that lies.

• Next.js Stale Page Verdict — measured across 14, 15 AND 16: the plain `await fetch()` is frozen on all three. Next 15 changed the caching default and the symptom did not change, so upgrading does not fix it. And on 14, `force-dynamic` re-renders the route and still serves a cached fetch.
• Next.js Server Prop Leak Verdict — measured: a server-only token in the page source with no `NEXT_PUBLIC_` anywhere, in a field the client component never reads, invisible to a JS-bundle scan.
• HTTP Cache Semantics — a response marked private, stored in a shared cache, serves one user's page to another.
• Cache Invalidation Race Verdict — a read that started before the write repopulates the cache *after* the invalidate. Stale forever, no exception.
• Device Capability Verdict — `/Safari/.test(ua)` is true for Chrome, Edge, Opera and Samsung Internet.

Why buy them together

Four of the five are caching decisions made in different layers — framework, HTTP, application — and the fifth decides which of them a given browser gets. They are usually debugged one at a time, because each one alone looks like a one-off.

Each ships with its own tests and is sold separately. This is the set, below the sum.