Now that we have the ability to mark topics as locked/closed thanks to https://phabricator.wikimedia.org/T415081 (Thank you!)

It would be nice to be able to capture the closure/lock rationale (i.e. Completed, Obsolete, etc.. ). Maybe the actual list could be defined in the cs tag like:

<comment-streams id="default" cs-rationales="Completed,Obsolete,Withdrawn">

If defined, the closure rationale would be selected during the lock/close event.

The closure rationale should also be quarriable by SMW