Cache Fileserver is an old project of mine which allows file upload/download. Files have IDs, but to download each client get's an unique link active only for his IP for a limited time. You can remove IDs altogether.

You can define your own device of terminal type (also see System  - Configuration - Devices you can see other defined Cache terminals) :

Here's an idea on how to do it without triggers altogether.

1. Set IsLeader property only in case member is a leader. So its 1 or NULL.

2. Add unique index on (Team, IsLeader). Unique index can have any number of NULL records.

3. If you try to add more than one leader, you'll get an error:

ERROR #5808: Key not unique: Utils.TeamMember:IsLeaderIndex:^Utils.TeamMemberI("IsLeaderIndex"," 1"," 1") [%SaveData+14^Utils.TeamMember.1:USER]

Sample code:

Class Utils.TeamMember Extends %Persistent
{

Property Team As %String;

Property Member As %String;

Property IsLeader(VALUELIST = ",1");

Index IsLeaderIndex On (Team, IsLeader) [ Unique ];

/// do ##class(Utils.TeamMember).Test()
ClassMethod Test(AddTwoLeaders = {$$$YES})
{
    do ..%KillExtent()
    write $System.Status.GetErrorText(..Add(1, "Alice"))
    write $System.Status.GetErrorText(..Add(1, "Bob"))
    write $System.Status.GetErrorText(..Add(1, "Clover"))
    write $System.Status.GetErrorText(..Add(1, "Dave", 1))
    if AddTwoLeaders {
        write $System.Status.GetErrorText(..Add(1, "Helen", 1))
    }
}

ClassMethod Add(Team, Member, IsLeader = "")
{
    set obj = ..%New()
    set obj.Team = Team
    set obj.Member = Member
    set obj.IsLeader = IsLeader
    quit obj.%Save()
}

}

You should have FHIR package, which includes dtls to transform hl7 messages into json or xml. You can either use that or write your own solution based on that.

How do you propose it should be handled instead?

You  provided two ways, by which you can control string/number output, and they seem to cover most of the cases.