hm, not sure if that does or doesn't work, but either way it shouldn't be necessary--you can just use :db/op :merge to get the same effect. :db.op/upsert is just there so you can update/insert docs on non-`:xt/id` keys, since XTDB already ensures that the :xt/id key is unique.

(As an aside, migrating to/adding support for XTDB 2.0 will provide a good opportunity to rethink Biff's transaction format and try to sand off some of the unintuitive edges like this...)

Ah! :db/op :merge did the trick! Just when I was about to rethink my whole approach.

I think I sussed out my mistake. When the :upsert didn't find the :xt/id I supplied, it created a new doc but instead of using the :xt/id I gave it, it rolled up a random uuid. Which makes sense and is exactly what the documentation told me what would happen. I just got so used to using :upsert with other attributes, I didn't think it through.

ah yes, that makes sense. in any case I think it'd be worthwhile to have a unified format for doing upsert, whether it's with xt/id or another key