What did I break and how?

Check the sear isn't hung up or jammed. Pull the bolt then while looking down into the rear of the bolt raceway pull & release the trigger several times. You should see the top of the sear rise up into & drop back down below the bolt raceway.

Did you remove the trigger guard from the stock?

If you did maybe the trigger & sear are swapped for position.

With the bolt out of the action, can you turn the cocking piece such that the small lug on the bottom of the cocking piece rides in the cam slot? Perhaps it’s broken or jammed here? 

A mystery so far. 

When you insert the bolt line the head up with the little spring, looks like a button, push down on the the bolt head then push the bolt in.

If it's not riding in it track it won't close properly.

Look at the removed bolt from the front.

Is the extractor spring sticking out?

Is there tension on the extractor claw?

If the "U" spring broke (a common problem) it could be causing the problem you describe?

Good news- the bolt now goes back in all the way!

Last night I thoroughly cleaned the rifle, broke the bolt down and cleaned/soaked everything really well. Looks as though the rifle hadn't been deep cleaned in a long time. Flushed out a fair amount of crud and can only guess that something had accumulated/stuck somewhere to cause the bind. Maybe if I had really bashed in the bolt it would have closed anyway but glad I didn't force it and everything works again now. 

Thanks again, Matt.