Function copy_worktree_files 

pub fn copy_worktree_files(
    source_worktree: &Path,
    target_worktree: &Path,
    paths: &[&Path],
    mode: ReflinkMode,
) -> Result<CopyOutcome, WorktreeError>

Copy all files from source_worktree into target_worktree, preserving directory structure and respecting ReflinkMode. Skips .git/ directories.

This is used after git worktree add to CoW-copy large build artifacts, node_modules, or other non-tracked files that an EcosystemAdapter might need.