Edge 156: daemon reports "DevToolsActivePort not found" when the file exists but the port is dead - caused by --remote-debugging-port on the default profile #977

Summary

The daemon's final error says DevToolsActivePort not found, but the file is there and the chrome://inspect/#remote-debugging toggle is already on. The file just points at a port nothing is listening on. The message and the suggested fix send you to tick a checkbox that is already ticked.

Trigger: the browser was started with --remote-debugging-port=9222 on the default profile. Edge 156 (chromium 136+ lockdown, same IsUsingDefaultDataDirectory() check as #264) then opens no devtools endpoint at all — the requested port never binds and the toggle path does not come up either — so the DevToolsActivePort file on disk is stale from the previous run.

Not a duplicate of #264 / #291 / #894

• daemon: Chrome 147+ default-profile CDP discovery fails (regression from #260) #264 / fix: BU_CDP_URL path in get_ws_url() fails on Chrome 147+ (default user-data-dir) — missing /json/version 404 fallback #291 were about /json/version returning 404 while the websocket still worked. Here nothing is listening on any port, so the DevToolsActivePort fallback has nothing to fall back to.
• Auto-launch never fires when Chrome is quit but another Chromium-family browser (Brave) is running: daemon reports "DevToolsActivePort not found" instead of chrome-not-running #894 is the "another chromium-family browser is running" path. Here the right browser is running, with the toggle on.

What I see

fatal: DevToolsActivePort not found in ['C:\Users\<user>\AppData\Local\Google\Chrome\User Data',
'C:\Users\<user>\AppData\Local\Google\Chrome SxS\User Data', ...,
'C:\Users\<user>\AppData\Local\Microsoft\Edge\User Data', ...] — enable
chrome://inspect/#remote-debugging, or set BU_CDP_WS for a remote browser

but the state is actually:

• %LOCALAPPDATA%\Microsoft\Edge\User Data\DevToolsActivePort exists — port 64302, /devtools/browser/<uuid> on line 2
• %LOCALAPPDATA%\Microsoft\Edge\User Data\Local State → devtools.remote_debugging.user-enabled = true
• nothing is listening on 64302, or on any other port
• the DevToolsActivePort mtime is older than the browser process start time — leftover from the previous run, the new browser never wrote it

so the real message is "found, but dead", not "not found".

Repro

1. edge 156, default profile, edge://inspect/#remote-debugging → tick "allow remote debugging for this browser instance"
2. quit edge completely
3. relaunch edge with --profile-directory=Default --remote-debugging-port=9222
4. run browser-use

Cross-checks that may help

• the same command without the flag works: edge writes a dynamic port to DevToolsActivePort and list_tabs() returns the live tabs
• --remote-debugging-port does work on a non-default profile — --headless=new --user-data-dir=<scratch> --remote-debugging-port=9333 binds 9333 and /json/version answers normally, so this is specific to the default profile
• the port the harness picks up changes on every browser start, so 9222 is usually closed even while everything is working — that part is expected
• the flag is not a broken process singleton. Launching the same command while edge is already running gives exit code 0, empty stderr and no second instance — identical to the same launch without the flag

Suggested changes

• tell "no DevToolsActivePort file" apart from "file present but port not listening", and include the port and the file mtime in the error
• when a supported browser is running and the toggle is on but no port is live, say the endpoint is not reachable and name the likely cause — a browser started with --remote-debugging-port on the default profile ends up with no endpoint at all on chromium/edge 136+. install.md currently lists three possible reasons for daemon alive FAIL and the actionable one is not among them; the recovery it points at ("tick the checkbox") is already done in this case
• --doctor reports chrome running [ok] + daemon alive [FAIL], which is the only hint that anything is wrong
• the recovery text says "start Chrome" and points at chrome://inspect/#remote-debugging — on windows the browser here was edge, and edge://inspect/#remote-debugging is the matching page (see also fix: _open_chrome_inspect() fails on Windows — webbrowser.open() can't handle chrome:// protocol #290 for the windows chrome:// handling)

Environment

OS:                  Windows 11 x64
browser version:     edge 156.0.4314.58
browser-harness:     0.1.13 (pypi)
python:              3.11.15

browser-harness doctor
  platform          Windows 10
  python            3.11.15
  version           0.1.13 (pypi)
  latest release    0.1.13
  [ok  ] chrome running
  [FAIL] daemon alive — see install.md
  [FAIL] active browser connections — 0
  [FAIL] Browser Use cloud auth — optional: browser-harness auth login