Have you tested this out? I'm slightly concerned because we do make fetch requests to the URL in some places throughout the code (here is an example). I have no idea how a service like this could work across network requests.

Yeah I have tested with the following code snippet:

import { launch } from "https://esm.sh/gh/lowlighter/astral@feat-support-existing-ws-endpoint/mod.ts";
const browser = await launch({
  browserWSEndpoint:
    "wss://chrome.browserless.io?token=******",
});
const page = await browser.newPage("http://example.com");
console.log(await page.evaluate(() => document.title));
await browser.close();

And it does work (at least with browserless.io, and an existing local browser as highlighted by the tests):

@lowlighter ➜ /workspaces/astral (feat-support-existing-ws-endpoint) $ ~/.deno/bin/deno run -A test.ts
Example Domain

However as you mentioned calling page.close() directly will fail as it cannot reach /json/close, but since it cleans the celestial websocket anyways, the tests weren't failing because there were no leaking ops as resources were still properly sanitized.

I'll make a few changes to address this 👍

Actually, if you could write a section in the docs about "connecting to remote browsers", that would be amazing!