Function find_unit_file 

pub fn find_unit_file(mana_dir: &Path, id: &str) -> Result<PathBuf, Error>

Find a unit file by ID, supporting both new and legacy naming conventions.

Searches for unit files in this order:

1. New format: {id}-{slug}.md (e.g., “1-my-task.md”, “11.1-refactor-parser.md”)
2. Legacy format: {id}.yaml (e.g., “1.yaml”, “11.1.yaml”)

Returns the full path if found.

Examples

• find_unit_file(mana_dir, "1") → .mana/1-my-task.md or .mana/1.yaml
• find_unit_file(mana_dir, "11.1") → .mana/11.1-refactor-parser.md or .mana/11.1.yaml

Arguments

• mana_dir - Path to the .mana/ directory
• id - The unit ID to find (e.g., “1”, “11.1”, “3.2.1”)

Errors

• If the ID is invalid (empty, contains path traversal, etc.)
• If no unit file is found for the given ID
• If glob pattern matching fails