gatsby: VS Code debugger broken (Exception: Inspector is already activated)

Gatsby has recently stopped working with defined debugger launch configurations in Visual Studio Code.

I don’t know if this was due to a change in Gatsby or in VS Code and/or its extensions; I just know it worked at some point in the last couple of months, and now it doesn’t.

Steps to reproduce

Update: I can reproduce this issue in a starter repo using the exact launch configuration from the docs:

launch.json

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Gatsby develop",
      "type": "node",
      "request": "launch",
      "protocol": "inspector",
      "program": "${workspaceRoot}/node_modules/.bin/gatsby",
      "autoAttachChildProcesses": true,
      "args": ["develop", "--inspect-brk"],
      "stopOnEntry": false,
      "runtimeArgs": ["--nolazy"],
      "sourceMaps": false
    },
    {
      "name": "Gatsby build",
      "type": "node",
      "request": "launch",
      "protocol": "inspector",
      "program": "${workspaceRoot}/node_modules/.bin/gatsby",
      "args": ["build"],
      "stopOnEntry": false,
      "runtimeArgs": ["--nolazy"],
      "sourceMaps": false
    }
  ]
}

This is the line throwing an unhandled exception:

https://github.com/gatsbyjs/gatsby/blob/7e83aced6b5c9fc421fd8f3b67b77269a6b59f09/packages/gatsby/src/commands/develop-process.ts#L67

This is the exception:

Exception has occurred: Error [ERR_INSPECTOR_ALREADY_ACTIVATED]: Inspector is already activated. Close it with inspector.close() before activating it again.
  at Object.open (inspector.js:137:11)

Some things I’ve tried adjusting without success:

• Changing "type": "node" to "type": "pwa-node" and/or setting debug.node.useV3 to true; either one should cause VS Code to use the new Node.js debugger
• Moving "--inspect-brk" to runtimeArgs or removing it entirely

Workaround

Auto-attach is not affected. If I set VS Code setting debug.node.autoAttach to true and then run node --nolazy node_modules/.bin/gatsby develop --inspect-brk in the terminal, the debugger attaches and Gatsby runs without exception.

Environment

  System:
    OS: Linux 4.19 Debian GNU/Linux 9 (stretch) 9 (stretch)
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    Shell: 4.4.12 - /bin/bash
  Binaries:
    Node: 12.18.3 - /usr/local/bin/node
    Yarn: 1.22.4 - /usr/bin/yarn
    npm: 6.14.6 - /usr/local/bin/npm
  Languages:
    Python: 2.7.13 - /usr/bin/python
  npmPackages:
    gatsby: ^2.24.52 => 2.24.52
    gatsby-source-sanity: ^6.0.3 => 6.0.3