browser run: response.text() returns comma-joined bytes, breaking response.json()

[ankitranjan7]

Summary

Inside the browser run QuickJS sandbox, response.text() returns the body's bytes joined by commas instead of the decoded text. response.json() is therefore broken for every network response.

Repro

webcmd --session <id> browser run --stdin --no-snapshot-diff <<'JS'
const pending = page.waitForResponse(r => r.url().includes('/products/1'));
await page.goto('https://dummyjson.com/products/1');
const response = await pending;
const t = await response.text();
return { type: typeof t, first80: String(t).slice(0, 80), len: String(t).length };
JS

Actual:

{
  "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
}

123, 34, 105, 100 are the byte values of {, ", i, d. Expected {"id":1,"title":"Essence....

Cause

src/browser/run/playwright-client/vendor/client/network.ts:732

async text(): Promise<string> {
  const content = await this.body();   // a plain Uint8Array under QuickJS, not a Node Buffer
  return content.toString('utf8');     // Uint8Array.toString() ignores the argument
}

Uint8Array.prototype.toString inherits Array.prototype.toString, which comma-joins the elements and discards the 'utf8' argument. There is no Node Buffer in the sandbox.

Knock-on effect

response.json() calls JSON.parse on that comma-joined string and fails with unexpected data at the end. normalizeExecutionError then matches /syntaxerror/i and reports it as BROWSER_RUN_SYNTAX_ERROR — telling the caller their program has a syntax error when it is valid JavaScript. Filed separately as #355.

Fix

The sandbox already injects a decoder for exactly this: decodeText in src/browser/run/playwright-client/quickjs-platform.ts, backed by __webcmdDecodeText in src/browser/run/runner.ts. this._platform is available on the class — see network.ts:393 for an existing use.

async text(): Promise<string> {
  const content = await this.body();
  return this._platform.decodeText(content);
}

The vendored client is bundled into src/browser/run/generated/playwright-client.js, so the bundle needs regenerating (see src/browser/run/playwright-client/README.md), and src/browser/run/playwright-client-build.test.ts may need updating.

Worth a regression test asserting response.text() returns decoded text for a known body.

Impact

In the internal task eval this cost roughly five wasted attempts in one scenario: the agent tried response.json(), then JSON.parse on the raw value, then several exploratory scripts, before working out that it had to decode comma-separated byte values by hand.

[ankitranjan7]

Correction to the Fix section above: this._platform.decodeText(content) is wrong and would be undefined at runtime. decodeText lives on the exported quickjsEncoding object in src/browser/run/playwright-client/quickjs-platform.ts, not on the Platform type — vendor/protocol/validatorPrimitives.ts shows the correct import pattern.

Fixed in #357, which also caught Request.postData() carrying the identical toString('utf-8') defect.