"PostHog + Next.js 16 App Router: the Suspense gotcha that silenced my analytics for 6 days"

I shipped a no-op stub of PostHogProvider.tsx on April 20. I told myself I would come back to it that afternoon. Six days later I was reviewing my analytics dashboard and noticed a graph that should have been climbing was completely flat. Every posthog.capture() in my Next.js 16 App Router app had been firing into a black hole. Including the one event I actually cared about: the waitlist signup. This is the post-mortem. Three gotchas, real code, and how I verified the fix in a way that did not d