Build errors fail silently

Build errors (apparently from missing modules, but I assume that there are lots of other causes) seem to result in a bad build that fails silently. The "bad build" in my case always results in the source files being copied as-is to the destination directory, which is _worse_ (IMO) than not copying anything. 😢

Start by reproducing the reported build with a missing module and trace how the bundler handles the resulting error. Determine where the failed build is reported and how source files reach the destination directory; done means build errors are visible and a failed build does not copy source files as-is.

Written by the indexing model from the issue text.