Review all potential panics in the entire codebase.

Review all potential panics.
Rewrite the code to return errors wherever it makes sense.
Comment on all cases where the panicking code is safe and explain why.

Cases:
1. `expect` or `unwrap` called in function returning a `Result`

Search the entire codebase for `expect` and `unwrap`, especially calls inside functions returning a `Result`. Review each occurrence, replace panicking code with error returns where appropriate, and document why any remaining panic is safe; completion requires all cases to be reviewed and explained.

Written by the indexing model from the issue text.