edgedb unlessConflict rewrite error

default.esdl

module default {
  abstract type Auditable {
    required property created_at -> datetime {
      readonly := true;
      default := datetime_of_statement();
    };
    property updated_at -> datetime {
      rewrite update using (
        datetime_of_statement()
      )
    };
    property deleted_at -> datetime;
    
    # Constraints
    delegated constraint expression on (
      .deleted_at > .created_at
    ) except (not exists .deleted_at)
    {
      errmessage := "deleted_at can't occur before created_at"
    };

    delegated constraint expression on (
      .updated_at >= .created_at
    ) except (not exists .updated_at)
    {
      errmessage := "updated_at can't occur before created_at"
    };
  }

  type User extending Auditable {
    required my_id -> int32 {
      readonly := true;
      constraint exclusive;
    };
    json_data -> json;
    single link data -> UserData {
      constraint exclusive;
    };

    constraint expression on (exists .data);
  }

  type UserData extending Auditable {
    single link user := .<data[is User];
    private_data -> str;
  }
}

migration.edgeql

CREATE MIGRATION m1plwaggy3dihp3fcs6ad3ejpttbiwxfvr73audkpcsvzangoretsa
    ONTO initial
{
  CREATE FUTURE nonrecursive_access_policies;
  CREATE ABSTRACT TYPE default::Auditable {
      CREATE REQUIRED PROPERTY created_at: std::datetime {
          SET default := (std::datetime_of_statement());
          SET readonly := true;
      };
      CREATE PROPERTY updated_at: std::datetime {
          CREATE REWRITE
              UPDATE 
              USING (std::datetime_of_statement());
      };
      CREATE DELEGATED CONSTRAINT std::expression ON ((.updated_at >= .created_at)) EXCEPT (NOT (EXISTS (.updated_at))) {
          SET errmessage := "updated_at can't occur before created_at";
      };
      CREATE PROPERTY deleted_at: std::datetime;
      CREATE DELEGATED CONSTRAINT std::expression ON ((.deleted_at > .created_at)) EXCEPT (NOT (EXISTS (.deleted_at))) {
          SET errmessage := "deleted_at can't occur before created_at";
      };
  };
  CREATE TYPE default::User EXTENDING default::Auditable {
      CREATE PROPERTY json_data: std::json;
      CREATE REQUIRED PROPERTY my_id: std::int32 {
          SET readonly := true;
          CREATE CONSTRAINT std::exclusive;
      };
  };
  CREATE TYPE default::UserData EXTENDING default::Auditable {
      CREATE PROPERTY private_data: std::str;
  };
  ALTER TYPE default::User {
      CREATE SINGLE LINK data: default::UserData {
          CREATE CONSTRAINT std::exclusive;
      };
      CREATE CONSTRAINT std::expression ON (EXISTS (.data));
  };
  ALTER TYPE default::UserData {
      CREATE SINGLE LINK user := (.<data[IS default::User]);
  };
};