I run it in bwrap so, even if I'm running on Linux, I don't pay the cost of some layered file system and building the docker image. I mount some directories read only, the project repos read write. A VM would provide more isolation but it's a matter of tradeoffs.

BTW, I just checked and my .gitignore files ignore .claude

Claude and any other program in my laptop could upload it anyway to any attacker controlled server. It's the usual threat analysis: who you want to defend against, what and the tradeoffs between cost of the defense and probability of the attack. Auto mode of not auto mode is in the cost of defense part IMHO.