Because of differences in how .on_conflict() works compared to .replace_into() the PostgreSQL backend wasn't correctly ensuring the unique constraint on user_uuid and atype wasn't getting violated.
This change simply issues a DELETE on the unique constraint prior to the insert to ensure uniqueness. PostgreSQL does not support multiple constraints in ON CONFLICT clauses.
This includes migrations as well as Dockerfile's for amd64.
The biggest change is that replace_into isn't supported by Diesel for the
PostgreSQL backend, instead requiring the use of on_conflict. This
unfortunately requires a branch for save() on all of the models currently
using replace_into.