[Bug?]: Only the last parallel task exit code is respected

[danewilson]

Self-service

• I'd be willing to implement a fix

Describe the bug

Yarn supports parallel tasks, however it's not clear how exit codes are handled. It appears that only the exit code of the last task affects the final exit code. If this is intentional, perhaps the docs should explicitly state this and outline a better use case, because the example given is yarn lint & yarn test, which I think in most scenarios you would want to error if either one of those commands errored.

To reproduce

Assuming there is a formatting error, running yarn error produces an error because prettier is last, whereas yarn no-error does not:

{
  "scripts": {
    "error": "eslint . & prettier .",
    "no-error": "prettier . & eslint ."
  }
}

Environment

System:
  OS: macOS 15.5
  CPU: (12) arm64 Apple M3 Pro
Binaries:
  Node: 22.14.0 - /private/var/folders/ds/6vsg08yd4w3f4h4_0p0p86cw0000gn/T/xfs-4d8e788a/node
  Yarn: 4.9.1 - /private/var/folders/ds/6vsg08yd4w3f4h4_0p0p86cw0000gn/T/xfs-4d8e788a/yarn
  npm: 10.9.2 - ~/.nvm/versions/node/v22.14.0/bin/npm
npmPackages:
  jest: ^29.7.0 => 29.7.0

Additional context

No response