When {{clj}}/{{clojure}} encounters any kind of problem while building the classpath ({{deps.edn}} config, environment) it is almost impossible to diagnose the problem because only the exception message is printed.
For example, in a proxied environment {{clj}} fails to resolve Maven dependencies with a generic one-line message:
Error building classpath. Failed to read artifact descriptor for org.clojure:clojure:jar:1.9.0-beta2
(I believe this error is due to the web proxy.)
Consider adding a 'debug' or 'verbose' or 'stacktrace' option that provides visibility into the underlying machinery (stacktrace), so that users have a better handle on diagnosing problems.