[Bug]: Chromium new_context({ proxy }) ignored when running inside Docker without CDP

[4dvisor]

Version

1.52.0

Steps to reproduce

import asyncio
import json
from playwright.async_api import async_playwright

TEST_URL = "https://api.ipify.org?format=json"
PROXY = {
    "server": "http://proxy_url:proxy_port",
    "username": "username",
    "password": "password", 
}

async def fetch_ip(context):
    page = await context.new_page()
    await page.goto(TEST_URL, wait_until="domcontentloaded")
    ip = json.loads(await page.text_content("body"))["ip"]
    await context.close()
    return ip


async def main():
    async with async_playwright() as p:
        browser = await p.chromium.launch(
            headless=True,
            proxy={"server": "per-context"},               # <-- required
            args=["--disable-blink-features=AutomationControlled"],
        )

        ctx1 = await browser.new_context(proxy=PROXY)
        print("CTX-1 IP ⇒", await fetch_ip(ctx1))

        await browser.close()

asyncio.run(main())

Expected behavior

CTX-1 IP ⇒ <IP-from-proxy>

Actual behavior

CTX-1 ⇒ <host-public-IP>

Additional context

When Chromium is launched with proxy={"server": "per-context"} inside a Docker container, no context created with browser.new_context(proxy=…) uses the proxy at all—all requests always fall back to the container’s outbound IP.

Environment

- Operating System: [Ubuntu 22.04]
- CPU: [amd64]
- Browser: [Chromium]
- Python Version: [3.12]
- Docker img: mcr.microsoft.com/playwright/python:v1.52.0-noble
- Other info:

[mxschmitt]

There is no need for per-context anymore since microsoft/playwright#17252 was fixed.

Does it also happen if you do it without?

Does it happen if you do it via the proxy in the launch() call?

[4dvisor]

Okay, I removed the per-context setting and changed it so that the proxy is set in the launch call, but it still uses the host IP address instead of the proxy.

[4dvisor]

Also, adding the proxy in both the launch and new_context calls still results in the host IP address being used.
Removing the per-context setting and only adding the proxy in the new_context call also uses the host IP address.