react#36741 — Hidden-tab Suspense reveal repro

Minimal repro for react#36741: Suspense boundaries streamed while the browser tab is hidden never reveal — the page shows a loading spinner forever.

The bug (React 19.3.0-canary, main branch)

When a page with streaming Suspense loads in a hidden/background tab:

1. Shell script requestAnimationFrame(function(){$RT=performance.now()}) never fires → $RT stays undefined
2. Server streams resolved content; $RC runs: sees typeof $RT !== 'number' → schedules requestAnimationFrame($RV.bind(null,$RB))
3. That rAF also never fires in a hidden tab → $RV (reveal) never runs
4. Boundary comment stays "$~" (pending), content stays in a hidden <div> — forever

Verified with Playwright (automated)

After 5s (hidden tab):
  $RT:                   undefined      ← rAF never fired
  $RB.length:            2              ← boundary stuck in queue
  rAF callbacks queued:  2              ← never dispatched
  fallbackVisible:       true           ← user sees spinner
  revealedVisible:       false          ← content in hidden <div>
  boundary comment:      "$~"           ← pending, not "$"

✅ BUG CONFIRMED

Run the repro

git clone https://github.com/sleitor/react-36741-repro
cd react-36741-repro
npm install
npm run dev   # Next.js 15 + React 19.3.0-canary (commit 92f4fda3, pre-fix)

Open http://localhost:3000, middle-click a link to open it as a background tab, wait 5s, switch to it — spinner never goes away.

The fix

facebook/react#36751: when document.visibilityState === 'hidden' at shell parse time, set $RT = performance.now() immediately (no rAF). Add a visibilitychange listener as fallback for Case B (tab goes hidden after shell load but before the rAF fires).

Affected versions

React canary / main branch builds that include the $RT timing mechanism (introduced after 19.1.0, targeting 19.2+). React 19.1.0 stable is not affected because it uses a different reveal path without $RT.