Function compute_dependency_order 

pub fn compute_dependency_order(
    groups: &mut [CommitGroup],
) -> Result<(), String>

Reorder groups in dependency order using Kahn’s algorithm.

Each group’s CommitGroup::dependencies lists IDs that must be committed first. The slice is sorted in place so every dependency precedes its dependents.

Errors

Returns an error string when:

• a dependency references an unknown group id,
• a group depends on itself, or
• a dependency cycle is detected.