fix(web): convert ReadableStream to Blob for all browser environments

[JohnsonChin1009]

Context

uploadFile() fails in browser environments (Chrome + Next.js/Turbopack) with:

Failed to upload file after 6 attempts
Failed to execute 'fetch' on 'Window': The provided ReadableStream is disturbed

As reported here in #396.

Root cause

createReadableStreamWithEvents in events.ts calls originalStream.getReader() inside the start() callback, which runs immediately when the wrapper stream is constructed. Chrome's fetch is stricter than Firefox/Safari — it considers the stream already "disturbed" when { body: ReadableStream, duplex: 'half' } is passed to fetch.

New Fix

toFetchBody in http.ts already converted ReadableStream → Blob for Firefox/Safari via isFirefoxOrSafari(). This PR extends that same conversion to all browser environments by replacing the guard with isBrowser, and removes the now-unused isFirefoxOrSafari function.

Testing

• Reproduced the bug on Chrome with Next.js 15 + Turbopack (exact environment from [Feature]: uploadFile fails with "ReadableStream is disturbed" in browser (Chrome) — web SDK retry mechanism incompatibility #396)
• Verified fix resolves the error on Chrome, Firefox, Safari, and Arc Browser (the browser that I use)
• Added unit tests for TurboHTTPService.post covering the Node.js fetch body path
• All 50 unit tests pass

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[fedellen]

hey @JohnsonChin1009 thanks for this!

we're having some trouble reproducing the issue in a chrome environment using the html example on the repo. the readable stream code path can be used for files over the memory constrains of the browser to post the whole stream to /tx without getting OOM during chunkingMode: disabled

accepting the PR as is will break that functionality. we believe the best way to unblock you here is that there should be a new parameter added to the factory like browserStreamMode: 'blob' | 'stream' | 'auto' -- where auto is the current unbreaking functionality and blob and stream set use the path the client wants

you're welcome to take a shot at that, should be just updating the turbo factory and drilling that parameter down to this layer