Return the value at position `[frame slot]` in `vm-state`'s
environment. This is similar to `(get-in env [frame slot])` but
throws if the index is out of bounds (which can only result from a
revue.util/env-value found in 2 defs, across 1 project.
Search for vars with similar names in all artifacts: env-value
Search for env value in the documentation of all artifacts.