auto-connect fails with Chrome M144+ chrome://inspect remote debugging

[jonathanglasmeyer]

Hey y'all, thanks for your work on agent-browser. I'm trying to use --auto-connect to attach to my regular Chrome profile (with all my existing sessions/cookies), and I'm running into an issue with Chrome M144+'s new remote debugging mechanism. Below is Claude Opus 4.6's assessment after a good bit of digging - hopefully it's somewhat useful? :)

Environment

• agent-browser: v0.13.0
• Chrome: 145.0.7632.76 (arm64)
• OS: macOS 15.3 (Darwin 24.6.0, Apple Silicon)
• Remote debugging enabled via: chrome://inspect/#remote-debugging UI toggle (not CLI flag)

Problem

--auto-connect fails despite PR #432 being merged:

$ agent-browser --auto-connect screenshot
✗ No running Chrome instance with remote debugging found.

DevToolsActivePort exists and contains valid data:

$ cat ~/Library/Application\ Support/Google/Chrome/DevToolsActivePort
9222
/devtools/browser/1ed17c43-53f8-4ecf-beb8-f3f33e7d5af2

Port 9222 is open (TCP connects), but Chrome M144+'s chrome://inspect server has no HTTP endpoints:

$ curl -v http://127.0.0.1:9222/json/version
< HTTP/1.1 404 Not Found

Explicit --cdp with the full WebSocket URL also fails (likely due to Chrome's user-approval dialog timeout):

$ agent-browser --cdp "ws://127.0.0.1:9222/devtools/browser/1ed17c43-..." screenshot
✗ Failed to connect via CDP to ws://...

Root Cause

Chrome M144+ chrome://inspect/#remote-debugging uses a WebSocket-only server with no HTTP discovery API. Confirmed by Chrome team in ChromeDevTools/chrome-devtools-mcp#772.

The current auto-connect flow in autoConnectViaCDP fails because:

1. probeDebugPort() calls /json/version → 404 → returns null
2. Fallback passes HTTP URL to connectOverCDP → Playwright internally calls /json/version/ → 404 → fails
3. Even with explicit ws:// URL via --cdp, the connection likely times out waiting for Chrome's user-approval dialog

How chrome-devtools-mcp (Google) solves this

Google's chrome-devtools-mcp works because it:

1. Reads DevToolsActivePort directly
2. Constructs ws://127.0.0.1:${port}${wsPath} without any HTTP probe
3. Connects via Puppeteer's WebSocket transport directly
4. Handles the user-approval dialog delay gracefully

Suggested Fix

1. When DevToolsActivePort exists, construct the ws:// URL directly from file contents and skip probeDebugPort() entirely
2. Pass the ws:// URL to connectOverCDP (Playwright should handle ws:// URLs without HTTP resolution)
3. Increase the connection timeout to allow for Chrome's user-approval dialog (user must click "Allow" in Chrome before the connection succeeds)
4. Consider adding a log message like "Waiting for approval in Chrome..." so the user knows to click Allow

References

• PR feat: add --auto-connect flag to discover and connect to running Chrome #432 (current auto-connect implementation)
• Chrome blog: Changes to remote debugging switches (Chrome 136+ security change)
• Chrome blog: DevTools MCP auto-connect
• ChromeDevTools/chrome-devtools-mcp#772 ("no HTTP endpoint for this mode")

[lukasmalkmus]

Yeah, same here.