Better exception

[apotonick]

I don't know how it could be done, yet, but the wiring error exception with anonymous classes is very hard to debug

Unrecognized Signal `#<Trailblazer::Activity::End semantic=:skip>` returned from #<Class:0x00005559038d3b30>. Registered signals are, 
#<Trailblazer::Activity::End semantic=:failure>
#<Trailblazer::Activity::End semantic=:success>
#<Trailblazer::Activity::End semantic=:key_not_found>

Maybe the activity could maintain a "name hint" and add this to the exception. Then it would be much more obvious this exception is coming from, say "song.deserialize.nested".

[apotonick]

Actually, this exception could be prevented in 99% of the cases if we had a compile time check when adding a Subprocess that has unwired termini.