Update: progress
(Won't go into entire backstory. The short version: shared custody of preteen Kid with alcoholic ex who is rapidly deteriorating, racking up DUIs and police calls, and lying and manipulating pretty much non-stop about drinking. After he tried to drive drunk with Kid earlier in the summer, I started moving towards sole custody).
We had our second mediation/arbitration meeting today, and the outcome was very positive. While we did not get to an actual legal change of custody, we did get an arbitrated agreement that Kid will continue to live with me full-time and ex will have graduated access. He has supervised short visits with SoberLink monitoring now, if all goes well for x number of months, he can have unsupervised short visits. If all goes well for another x months, he can have unsupervised longer visits. And so forth (the "x" numbers are to be determined by the arbitrator, who has the powers of a judge to draw up court-enforceable orders).
This is a good thing because it supercedes our (outdated) divorce order which specified shared parenting. It's also the first legal document in which ex acknowledges that he has a problem with addiction, that this prevents him from participating fully in Kid's life, and that his access to Kid will be restricted as a result. It sets a precedent which I can draw on if ex gets worse.
It also sets up an incentive system. If ex complies with SoberLink, doesn't drink around Kid, stays out of trouble with police and behaves, he gradually gets more time with Kid. If any of these things happen, he gets "sent back" to no visitation. This system is good because it's no longer me being the bad guy making decisions about not letting Kid see Dad, it's a document which Dad has agreed to and which a judge has ordered. Ex also can't pressure me to give him more access with Kid.
I expect that ex will screw this up pretty soon - his usual cycle is 2-3 months between disasters. If/when he does, I'm in a much stronger legal position to say "okay, we're back to stage 1, no access at all". And having a court order in which ex acknowledges his addiction problems (the equivalent of "under oath") could be valuable.
This is as enforceable as an outcome from a trial would have been, and it was much cheaper and shorter, even though it felt like it was taking forever. I don't have the actual wording yet as the judge needs to write it up in proper legalese. I know that this won't prevent ex from drinking and screwing around in Kid's life, but it gives me leverage. And now that we both acknowledge that Kid is living with me full-time because of her father's drinking, he has to start paying child support.
Whew! (for now)