" Combined with this only happening in a corner case (stale sessions) and the difficulty of reproducing the issue, it took us over a week to discover and confirm the root cause"

I don't know about others, but sessions that are idle > 1h are definitely not a corner case for me. I use Claude code for personal work and most of the time, I'm making it do a task which could say take ~10 to 15mins. Note that I spend a lot of time back and forth with the model planning this task first before I ask it to execute it. Once the execution starts, I usually step away for a coffee break (or) switch to Codex to work on some other project - follow similar planning and execution with it. There are very high chances that it takes me > 1h to come back to Claude.

It's likely a corner case for their developers. The dangers of working on a project is assuming user behavior like your own.

Yeah and that statement also speaks to their test rigor if they make a change that big without thoroughly testing the edge case they're modifying.