Does the sqlite3 cli (not python one) ignore trailing whitespaces?

Yes. The sqlite3 cli works normally on sql statements with trailing or leading whitespaces.

Trailing whitespaces for dot commands are also ignored, although leading ones are not.

$ sqlite3↵
sqlite> .quit␣↵
$ 

$ sqlite3↵
sqlite> ␣.quit↵
    ... ↵
    ... ↵

There was a missed space and redundant newline in the error message. #133807 fixes this.

No, the missing space is not introduced here but from this line of #133461. I left a comment there a month ago but the comment was labeled as "Pending", I am not sure whether it was successfully sent and Stan received it or not. This PR uses self.write() in which the newline is needed, otherwise the output is mixed with the next shell prompt on the same line.

@tanloong, the “pending” label means that the comment won't be sent until you “finish your review”:

Ah, sorry. I thought you were the last one to touch this code.

It is a common error to add a comment but forget to publish it.