[diegosouzapw]

Closes #16245

Root cause

React Fizz's $RC reveal runtime gates the first Suspense boundary swap on requestAnimationFrame unless the global $RT is already a number. rAF never fires in a hidden/occluded tab, and src/app/loading.tsx makes every route stream behind a Suspense fallback, so "Loading OmniRoute..." stays until the tab is shown. Upstream: React #36741, Next.js #95588.

What changed

• src/shared/utils/hiddenTabReveal.ts: exports HIDDEN_TAB_REVEAL_SCRIPT, which seeds window.$RT = performance.now() when document.visibilityState === "hidden", so $RC takes the setTimeout path.
• src/app/layout.tsx: injects it as the first <head> script via dangerouslySetInnerHTML, the same pattern as the existing pre-hydration scripts (no nonce handling exists there).
• Changelog fragment changelog.d/fixes/16245-hidden-tab-reveal.md.

Regression test

tests/unit/hidden-tab-suspense-reveal-16245.test.ts (jsdom, rAF stubbed as never firing, real React streamed HTML): imports the shipped constant and asserts the fallback is replaced; plus a static guard that layout.tsx injects it.

• RED (without the script): AssertionError: fallback 'Loading OmniRoute...' must be gone.
• GREEN (with the shipped script): 2 pass, 0 fail.
  The no-script baseline case was dropped from the committed file because it would fail by design.

Gates run

eslint (with suppressions) clean, prettier, typecheck:core exit 0, check-file-size, check-complexity, check-cognitive-complexity, check-changelog-integrity all OK, sibling layout tests (material-icons-self-hosted, hydration-extension-attrs) pass, pre-commit hooks passed.

Manual production-build browser check was not done by the author; the owner validates it. Caveat: relies on the private React global $RT; if renamed upstream the script becomes a no-op.

⚠️ base-red inherited: #15306 — full unit suite ceiling, Vitest MCP audit shutdown, integration suite ceiling, package-artifact, tarball boot-smoke, ci.yml lint check:ai-attribution range step (not touched by this PR).

[github-actions]

CI Coverage Report

• Coverage job: skipped
• PR test policy: success

Coverage artifact was not available for this run.