I looked up Family Code Sections 17400-17440, and 5600-5604 but could not find the answer to this question:

While the process of first opening a case is described in the above codes, (and how the other party can object to the case opening), there is nothing about what happens after one side has dropped the case, but the other side wants it reopened.

Treat it as a new request to open the case with DCSS.

Are you saying that I should now file paperwork to initiate a case with DCSS, as if it were a new case?

Will any ruling at upcoming hearing made this month be in jeopardy during this process?

The hearing is already scheduled so it should move forward. If she trys to say that it should be transfered because DCSS is no longer involved advise the court that you have opened the case with them.

I'm sorry. But just to be clear: Do I file actual paperwork to "open" the case with DCSS, or do I say I have opened the case because the Commissioner already agreed that I opened it back up, by asking openly in Court that day, and the Court agreeing it was reopened?

If the agency is not able to assure you that the case will remain open because you object to its being closed then file to open it yourself. This way you have your bases covered and can accurately represent to the court at hearing that you objected to closing attempted by her and filed for the agency to assist yourself as well. The only problem you can encounter with opening a case is being advised that a case is already open.

Ex wants to contest the case being re-opened. She says I needed to "officially" contest it being closed and/or "officially" opened it after she closed it, and thus allow her to properly object to it being reopened.

I have no idea what she means by "offically" contesting closure. I also do not believe there is anything more specific than Family Code, Section 17400 as to who can request assistance. It is general policy of the Department to assist upon the request of any party.

I see what you mean. A case can be opened upon the request of any party.

I'm curious about the actual procedure, though, which includes the opportunity for the OTHER side to contest a case opening. Ex is objecting that since I haven't "officially" opened the case that she closed, that she is being denied the opportunity to contest my opening the case.

I am not aware of any contest that can be made to the opening of a case. The case gets opened and then there may be argument about what if anything there is to enforce.