Reproduce

npm install
npm run dev
# Open http://localhost:5173 — the tab will freeze.

The Bug

A page freezes (infinite hang, no error output) when all of the following are true:

1. hydrateRoot is used (not createRoot)
2. The server HTML differs from what the client renders (hydration mismatch)
3. A component throws an error during render
4. React.Activity is present in the component tree