Almost certainly the motor has seized!
Just because you can rotate the motor now with the kickstart doesn't really mean anything. Once a motor has completely cooled after a seize then it 'can often' release and the motor then be able to turn over.
I am an expert with seizures (mc28 sudden loss of coolant
!!!) and many seizures during my kart racing days trying to run in a freshly built motor too quickly for a race.
Cold seizes are also quite common...had a few of those...always make sure engine is fully warmed up before giving it full beans... ?
One thing that says it all sadly about your motor is that you say that it has no compression....e.g..damaged rings at best.
There is no other action other than a top end strip down. DON'T try running it as you will probably do even more damage.
Hope this helps..not good news though.
Mike
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I don't mind dying...I just don't want to be there when it happens!