you are comparing a web API of a central server to a local API of a library
which is completely wrong, for your information, ArcaneChat uses its own core that is a fork of the official chatmail core with some modifications and additions
you can do the same and of course you could implement a chatmail core in C# if you wanted to but it is a lot of useless uninteresting work reinventing the wheel while you didn't deliver anything useful to the users
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