Fallible systems need to report failures

[alice-i-cecile]

As of #16589, systems which fail will just silently do nothing.

This is a fine choice to offer, but not a good default behavior since it masks real bugs in users games. Until we get a more sophisticated error handling mechanism in place, we should make this panic for now.

[alice-i-cecile]

I've opened this issue to ensure that we don't ship the current behavior. The suggestion to panic is a reasonable stop-gap, and should have been done in the initial PR.