React 19.2 stream batching causes SSR HTML to omit resolved loader data in React Router v7

[bendvc]

Reproduction

https://stackblitz.com/edit/github-2kri2mpb?file=app%2Froutes%2Fdemo.tsx

You'll have to copy this demo and run it locally in order to view the document contents in the network tab as this wasn't possible in stackblitz.

You'll see that the fallback loader is showing in the html even though I'm forcing the isbot flag to be true, this worked differently before React 19.2

System Info

OS: macOS (any)

Node: 20.x

React: 19.2.x

React DOM: 19.2.x

React Router: v7.x (framework mode, streaming SSR)

Browser: Chrome (behavior also affects non-JS crawlers and bots)

User Agents Affected:

LLM crawlers / AI bots (no JS execution)

Link preview bots

Internal indexing bots

Used Package Manager

pnpm

Expected Behavior

When React Router detects a bot user agent and switches to its path to onAllReady, the generated HTML should contain all resolved loader data, matching pre–React 19.2 behavior.

Specifically:

All loader promises are awaited

The final HTML contains fully rendered route content

No client-side JavaScript execution is required to see resolved data

This behavior is important for crawlers and bots that do not execute JavaScript or process streamed chunks.

Actual Behavior

After upgrading to React 19.2, SSR HTML generated by React Router v7 no longer includes all resolved loader data, even when:

A bot user agent is detected

The server waits for all loaders to resolve

Instead:

The initial HTML still contains Suspense fallbacks or incomplete content

Resolved data only appears after client-side hydration and streamed updates

Crawlers that do not execute JavaScript observe incomplete or empty content

Setting progressiveChunkSize: Infinity in the server entry restores the previous behavior, but this feels like a React-internal workaround and changes React Router’s default SSR semantics.