"pending" should not imply valid

[dmnd]

It's a dodgy to equate "unchecked" and especially "pending" with valid.

Arguably it's client code's responsibility to know when external validations are pending, so the problem is worse for internal errors.

"unchecked" and "pending" get exposed to client code during the render phase (not sure about post-commit though). I wonder if the sequence render, user event handler (e.g. onSubmit), render, commit could occur, where this could very likely cause a bug in client code.

Possibly related to #44.

Originally posted by @dmnd in https://github.com/flexport/formula-one/pull/75