The server now discovers a command which it cannot parse, perhaps because of a user typing error. Resynchronizing an interaction as described in section 4 above. Sends an error message. Resumes interpretation of input. The dual of B above.
B resumes forwarding A's output to the terminal.
This achieves the effect of flushing all output from A, up to the point where A saw the timing mark, but not output generated in response to the following command.