Function storage_key 

pub fn storage_key(repo: &str, base_sha: &str, head_sha: &str) -> String

The localStorage key a review document is filed under.

The key pins the exact endpoint SHAs on purpose: line numbers are only meaningful against the diff they were written on. Regenerating the same diff finds the same comments; new commits get a fresh store (carry comments over with export → import, where review::ReviewDocument::merge applies).