> Is there any mechanical pencil that's meant to toss around in a bag and survive?

I'm not sure exactly what the failure mode is that you're experiencing, but the Rotring 800[0] is retractable. I've gotten a lot of use out of my Rotring 600 but wish I had bought the 800 to be able to retract and protect the lead sleeve.

[0] https://www.rotring.com/pens-pencils/pencils/rotring-800/SAP...