Thank you for the explanation, and software 
. Are you describing how you wish it to work (to help guide its development)? Current behavior (for me and others) is two WindowsService and one Server, as explained by you in [SOLVED] Is it ok that I see 5 processes of Duplicati in Windows Task manager?. Seen using Process Explorer, below is how a very fresh (empty standby list) service start of base version 2.0.3.10 plus update to 2.0.3.11 comes up. The (too big for me) 80 MB read in the parent WindowsService is the integrity check and update selection for child WindowsService, and I think that path is concatenated here to set the Server path.
On shakier ground (haven’t had this in debugger lately), if Server should be paired (so MAGIC_EXIT_CODE works) that was my test to prevent AUTOUPDATER_Duplicati_INSTALL_ROOT=C:\Program Files\Duplicati 2 from inheriting down from child WindowsService. Its absence in Server stops the child prevention found here. Another possible path to activation would be to have child WindowsService propagate special exit code from Server up to parent WindowsService to then repeat its choose-and-launch. Currently restart is a simple loop which seems like it should just repeat the original launch, which is what it seems to do for me. Earlier picture:
where I now notice Server has done a lot of reads too (integrity checking?) even though it didn’t launch child. Still trying to sort out wishes from actuals, but seemingly actuals vary. @mnaiman and I see solid failures… For anyone seeing a radically different process view, I wish I could see it. Are some really getting Server pair from a WindowsService install? Pairing is fine for direct TrayIcon or Server starts, but that’s not this article…