Background

#6215
This subitem is focused on https://github.com/dotnet/msbuild/blob/main/src/Shared/LogMessagePacketBase.cs#L377

Suggested approach

Define custom build event type with de/serialization methods similar to #8779 (however without any type hierarchy/ overloading/ reflection etc - just single type and bag of strings), allow only such custom events - unles opted-out via changewave
Seal our BuildEventArgs hierarchy - to prevent subclasing (handling of subclasses would require registration of those during startup of nodes)