fix(browser): decode response bodies as UTF-8 text in the run sandbox

[ankitranjan7]

Closes #354

What was wrong

Response.text() in the vendored Playwright client did content.toString('utf8') on the body. Under QuickJS there is no Node Buffer, so the body is a plain Uint8Array and Uint8Array.prototype.toString falls through to Array.prototype.toString — comma-joining the byte values and discarding the 'utf8' argument. response.json() then JSON.parsed that string and always failed.

Request.postData() had the identical defect (?.toString('utf-8')), so it is fixed in the same commit.

The fix

quickjsEncoding.decodeText(...) from src/browser/run/playwright-client/quickjs-platform.ts, the same injected UTF-8 codec vendor/protocol/validatorPrimitives.ts already uses for base64.

Note: the issue suggested this._platform.decodeText(content). That would have been undefined at runtime — decodeText lives on the exported quickjsEncoding object, not on the Platform type. Importing quickjsEncoding is the pattern the vendored protocol files already follow.

src/browser/run/generated/playwright-client.js is regenerated with node scripts/build-playwright-sandbox-client.mjs, vendor-manifest.json's vendorSha256 is updated for the vendor edit, and the README's "Local patches" list documents it. playwright-client-build.test.ts needed no change; its --check passes.

Before / after

Same repro, same daemon, only the bundle swapped between runs.

Before:

{
  "type": "string",
  "first80": "123,34,105,100,34,58,49,44,34,116,105,116,108,101,34,58,34,69,115,115,101,110,99",
  "len": 5329,
  "jsonError": "unexpected data at the end"
}

After:

{
  "type": "string",
  "first80": "{\"id\":1,\"title\":\"Essence Mascara Lash Princess\",\"description\":\"The Essence Masca",
  "len": 1510,
  "id": 1,
  "title": "Essence Mascara Lash Princess"
}

Verified

• End-to-end against https://dummyjson.com/products/1 through a daemon restarted from this branch; response.json() returns real fields.
• New regression test in src/browser/run/runner.test.ts covering postData(), text(), and json() against the in-test example.test routes (no network). It fails with the old bundle (unexpected data at the end) and passes with the new one.
• npx vitest run --project unit: 117 failures both before and after on the same checkout — identical set, all pre-existing/environment-related; no new failures, and the suite gains the one new passing test.
• npx tsc --noEmit: clean.
• node scripts/build-playwright-sandbox-client.mjs --check: clean.

Out of scope, noticed in passing

• APIResponse.text() in vendor/client/fetch.ts has the same toString('utf8') bug, but it is unreachable: every APIResponse comes from _innerFetch, which evaluates options.params instanceof URLSearchParams unconditionally, and URLSearchParams is not defined in the sandbox — so page.request.get(...) throws ReferenceError before any response exists. Left untouched per browser run: response.text() returns comma-joined bytes, breaking response.json() #354's scope; the URLSearchParams gap is a separate bug worth its own issue.
• Buffer.byteLength / Buffer.from remain in network.ts fulfill/override paths — same missing-Buffer family, different symptom, not touched here.
• The /syntaxerror/i misclassification this bug triggers is browser run: syntax-error classifier mislabels runtime JSON.parse failures #355 and is deliberately untouched.

🤖 Generated with Claude Code

[github-actions]

🟠 Maintainer review suggested — low confidence

The automated review could not reach a fully supported conclusion.

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• The automated review returned an invalid structured result.

This review is advisory and does not block merging.