Make a plan for more user-friendly errors

[artoonie]

NPEs and similar issues are inscrutable to users. Make a plan for how to make these error messages more useful.

Requirements:

1. The plan does not rely on avoiding 100% of NPEs and other exceptions. It tries to provide useful messages, even when an unexpected error occurs.
2. The plan is cross-checked with recent Uncaught Exception issues to validate that it would have provided nicer error messages for them, even in lieu of the actual fix provided for that specific Uncaught Exception.

The output of this Issue is another Issue that is scoped, prioritized, and estimated.

This is a followup to #632