## What changed
- Export `read_sensitive_file_to_string` from `codex-exec-server`.
- Require the opened path to be a regular disk file and avoid following its
final symlink component on Unix or reparse point on Windows.
- Read valid UTF-8 file contents asynchronously and return I/O errors for
unsupported inputs.
## Testing
Add tests covering regular files, directories, and symlinks.
GitOrigin-RevId: 68809e94c0d3719e5685c064f9610a0455ffd8d7
