Job Scripts: No env name in exec results in "unknown error"

When executing a job script and calling exec like so:

```
const res = await exec(123)
```

the script silently does not throw.

when wrapping it in a try catch like:

```
try {
  const res = await exec(123)
} catch(e) {
  log(e)
}
```

we get a "unknown error" log.

The exec call should either work or show a useful error message to the user, with or without try catch.