[DoctorGuidance]

Closes #15486

Problem

In React Router 8's <Scripts /> component, the initial inline SSR script sets up the streaming handoff via:

window.__reactRouterContext.stream = new ReadableStream({
  start(controller) {
    window.__reactRouterContext.streamController = controller;
  }
}).pipeThrough(new TextEncoderStream());

In Chrome Mobile iOS (and other WKWebView-based apps like Google Search), Chrome injects JavaScript via WKUserScripts at documentStart that intercepts or wraps ReadableStream.prototype.pipeThrough and TextEncoderStream. This causes mutual recursion between injected handlers (Tk ↔ Rk), which overflows WKWebView's restricted JS call stack and throws RangeError: Maximum call stack size exceeded.

Because this error occurs in the first inline script of the page:

1. window.__reactRouterContext.stream and streamController are never initialized.
2. Subsequent inline <script> tags from <StreamTransfer> fail with TypeError: Cannot read properties of undefined (reading 'enqueue').
3. Hydration fails completely, leaving the app non-interactive on Chrome Mobile iOS.

Solution

Replace pipeThrough(new TextEncoderStream()) with a manual TextEncoder wrapper directly inside the ReadableStream start handler. This eliminates both pipeThrough and TextEncoderStream from the inline script while preserving the exact same ReadableStream<Uint8Array> output and enqueue/close/error controller contract for single fetch streaming:

window.__reactRouterContext.stream = new ReadableStream({
  start(controller) {
    var enc = new TextEncoder();
    window.__reactRouterContext.streamController = {
      enqueue: function(c) {
        controller.enqueue(typeof c === "string" ? enc.encode(c) : c);
      },
      close: function() { controller.close(); },
      error: function(e) { controller.error(e); }
    };
  }
});

Testing

• Added regression test in packages/react-router/__tests__/dom/ssr/components-test.tsx verifying the inline SSR script renders without pipeThrough or TextEncoderStream.
• Updated test mock stream controller in components-test.tsx and verified all 25 SSR and hydration tests pass.
• Verified TypeScript compilation (tsc --noEmit) passes with zero errors.

[brophdawg11]

closing for the same reason #15487 was closed