stop_on_unknown doesn't work

Explicit raises are now inside the block. The entire mechanism seems to have been neglected, as it's application is uneven.

Start by tracing the stop_on_unknown option-handling entry point and reproduce a case where explicit raises occur inside the block. Compare the behavior across the paths that handle unknown options, then verify that stop_on_unknown consistently produces the intended result without changing unrelated error handling.

Written by the indexing model from the issue text.