fnm exec fails with "program not found"

[thw0rted]

All my package scripts run fine under modern Node (v18 LTS or v19), except for tests, due to a longstanding issue with the older version of Angular we're stuck with. I'd like to use fnm to default to the latest build of v18 -- this works fine! -- while running just this one script in the latest v14 release, currently 14.21.2.

I've tried fnm exec --using=v14.21.2 yarn run test but that fails with

thread 'main' panicked at 'Can't spawn program: Error { kind: NotFound, message: "program not found" }', src\commands\exec.rs:79:14
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

I tried RUST_BACKTRACE=full but this is not enlightening:

   0:     0x7ff767d7c6b2 - <unknown>
   1:     0x7ff767d9f46b - <unknown>
   2:     0x7ff767d74efa - <unknown>
   3:     0x7ff767d7f284 - <unknown>
   4:     0x7ff767d7eeba - <unknown>
   5:     0x7ff767d7fa71 - <unknown>
   6:     0x7ff767d7f97d - <unknown>
   7:     0x7ff767d7d3bf - <unknown>
   8:     0x7ff767d7f640 - <unknown>
   9:     0x7ff767e378c5 - <unknown>
  10:     0x7ff767e37a43 - <unknown>
  11:     0x7ff7679d3f8b - <unknown>
  12:     0x7ff7679d5cd4 - <unknown>
  13:     0x7ff7679bd862 - <unknown>
  14:     0x7ff7679b6d96 - <unknown>
  15:     0x7ff767991f6c - <unknown>
  16:     0x7ff767d6d03e - <unknown>
  17:     0x7ff7679be2ec - <unknown>
  18:     0x7ff767e15d8c - <unknown>
  19:     0x7ffa5ce526bd - BaseThreadInitThunk
  20:     0x7ffa5e50dfb8 - RtlUserThreadStart

fnm 1.33.1 under Git Bash (msys), if that makes a difference.