We have a refactoring (shipping in 1.10.520) which assumes we are inferring on implements?
The expected optimization in that commit is actually not in play. If you look at the generated source for count for example, you don't see coll.cljs$core$ICounted$_count$arity$1.
I think this is a simple mixup / oversight that we didn't see with respect to implements? and instance?.
CLJS-3140.patch passes CI
CLJS-3140.patch passes Canary
CLJS-3140.patch added to Patch Tender