Consider including failing command in error message

Commands are echoed, so finding the last command that was run before an error is possible. However, if the last command produced a lot of output, this can be difficult. To make this slightly easier, we could include the failing command in the error message, either always, or just when `--verbose` is set.

This is an issue that I personally haven't run into, so feedback on whether or not this would be helpful is appreciated!

The issue names no files, tests, or entry points. Start by tracing how just echoes commands and formats errors, then compare the always-on and --verbose alternatives; done requires a decided behavior for including the failing command and tests covering the selected wording.

Written by the indexing model from the issue text.