tasks.json watcher launched by debugger never flags as a ready background task

[tigerhawkvok]

Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version:
  Version: 1.58.2 (user setup)
  Commit: c3f1263
  Date: 2021-07-14T22:10:15.214Z
  Electron: 12.0.13
  Chrome: 89.0.4389.128
  Node.js: 14.16.0
  V8: 8.9.255.25-electron.0
  OS: Windows_NT x64 10.0.19043
• OS Version: Windows 10 19403.1110

Steps to Reproduce:

1. Have a prerequisite prelaunch task for the debugger to run that must be in the background during the debug session
2. Run the debugger

I'm trying to run my debug environment as a Poetry session, so I can properly debug encapsulated.

So, my launch.json is straightforward:

        {
            "name": "Poetry",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "localhost",
                "port": 5710
            },
            "preLaunchTask": "poetryDebugSession"
        }

and I adapted my tasks.json to try to launch debugpy in Poetry first (this works if I manually run the command in the terminal then run the launch.json without the preLaunchTask)

{
            "label": "poetryDebugSession",
            "type": "shell",
            "command": "poetry",
            "args": [
                "run",
                "python",
                "-m",
                "debugpy",
                "--log-to-stderr",
                "--wait-for-client",
                "--listen",
                "5710",
                "${relativeFile}"
            ],
            "presentation": {
                "panel": "dedicated",
                "clear": true
            },
            "group": "test",
            "isBackground": true, // probably redundant now
            "runOptions":{
                "instanceLimit": 1
            },
            // This task is run before the launch.json task. Since it needs to run in the
            // background and not wait for completion, though, we need to jump through hoops
            "problemMatcher": [
                {
                    "owner": "python",
                    "fileLocation": "absolute",
                    "pattern": [
                        {
                            "regexp": "^\\s+File \"(.*)\", line (\\d+), in (.*)$",
                            "file": 1,
                            "line": 2
                        },
                        {
                            "regexp": "^\\s+(.*)$",
                            "message": 1
                        }
                    ],
                    "background": {
                        "activeOnStart": true,
                        "beginsPattern": "^D[0-9\\.: \\+]+wait_for_client",
                        "endsPattern": ".*",
                    }
                }
            ]
        }

When I start debugging, the task is properly launched, and debugpy gets all the way to the message I am waiting for that I want the preluanch task to be marked as "ready":

> Executing task: poetry run python -m debugpy --log-to-stderr --wait-for-client --listen 5710 d:\path\to\myfile.py <
# stuff

I+00000.344: pydevd is connected to adapter at 127.0.0.1:61443

D+00000.344: wait_for_client()

I could have sworn I had this working last week but as of 1.58.2 after a restart this morning it doesn't progress past wait_for_client() display, so the debugger never attaches. I'm also a little suspicious that ${relativeFile} includes a full path in my output but that probably doesn't matter.

[weinand]

/extPython