Yarn is running with the wrong version of Node

[mikrostew]

Repro

Remove your system node (or rename the binary).

In a project, setup the toolchain:

$ notion use node 10
$ notion use yarn 1.7

$ cat package.json | jq '.toolchain'
{
  "node": "10.10.0",
  "yarn": "1.7.0"
}

Running node works, but yarn fails:

$ node --version
v10.10.0
$ yarn --version
Yarn requires Node.js 4.0 or higher to be installed.

Cause

When the yarn shim runs, it sets the PATH wtih env::path_for_installed_node(), which strips out the Notion bin directory . When the actual yarn script is run with that PATH, it looks for node. But it doesn't see the Notion node shim, because it is not on the PATH. So it uses whatever is on the PATH, which is the system node, or nothing.