"package_config.json not found" error when connecting to Dart web app

[DanTup]

While investigating https://github.com/Dart-Code/Dart-Code/issues/5027 I tried connecting DevTools to a web app to see if I could repro the issue outside of VS Code. When I did, I got this error printed:

PS C:\Dev> dart devtools
Serving DevTools at http://127.0.0.1:9100.

          Hit ctrl-c to terminate the server.
package_config.json not found at: "file:///C:/Dev/Test%20Projects/dartcode_5027/web/main.dart/.dart_tool/package_config.json"
package_config.json not found at: "file:///C:/Dev/Test%20Projects/dartcode_5027/web/main.dart/.dart_tool/package_config.json"

Maybe similar to https://github.com/flutter/devtools/pull/6644?