Diagnosing a Teammate's "Lost Work" After /rewind

A teammate messages you, frustrated: "I used /rewind to undo a bad edit Claude made, and now a bunch of other work is just gone too — a file I know Claude created is missing, and some lint fixes a subagent made earlier in the session disappeared. Checkpointing is broken."

1. Before concluding checkpointing is broken, what specific questions would you ask your teammate to narrow down what actually happened?
2. Give the two most likely mechanical explanations for what they're describing, tied to specific, documented checkpoint limitations.
3. Explain what recovery options exist for each of the two explanations you gave.