- Extended short-form diff URL parsing to treat `<scheme>://N/diff` as a diff path across schemes, so `issue://N/diff` now follows the issue no-diff rejection path.
- Kept repository listing behavior unchanged for `<scheme>://owner/diff` by limiting diff short-form disambiguation to numeric hosts.
- Added regression coverage asserting `issue://9/diff`, `issue://9/diff/all`, and `issue://9/diff/3` now reject with the issue no-diff error.