Duplicate File Groups

Implement find_duplicate_files(files), a repository scan helper that groups files with identical content.

Requirements

• Input is a dictionary from path to text content.
• Return only duplicate groups with at least two paths.
• Sort paths inside each group.
• Sort groups by their first path.
• Raise ValueError instead of skipping any invalid path: empty path; any path segment equal to "", ".", or ".." after splitting on / (covers empty path, ., .., repeated slashes, and trailing slashes such as "", ../secret, src//app.py, src/./app.py, src/).
• Different paths are distinct files; group by exact content equality.

Example

Constraints

• Keep the scan in memory.
• Work only from the input map.
• Make output deterministic.