[racket] What's the idomatic way to handle system call errors?

I'm using racket/system to make some calls to other processes, which upon
failure write to standard error. What's the proper way to handle this? I've
been using with-output-to-string to get the output, but I don't know how I
can turn an error response from the external system command into something
in Racket I can work with. Is there some idiomatic with-error-as-exception
form or something similar that says "if this thunk writes to standard
error, throw an exception with the output in the message"?
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