It was agreed at some point that validation errors in commands wouldn't be exposed immediately through the current error scope, but instead would just change the state of the encoder and not be exposed to the error scope until finish().

However once the command encoder has already been finished, what should happen when a command is attempted anyway?

1. Silently fail.
2. Raise an error to the error scope even though encoding commands don't usually do that. (Dawn does this.)
3. Change encoding commands to normally raise errors to the error scope.
4. [EDIT:] Raise an exception if the content-side state is "finished" (or 4b: if it's wrong at all). Currently the spec says "encoder state" (open, render pass, compute pass, or closed) is a content-timeline state, actually, so spec-wise this is easy.