Function find_filesystem_workspace_root 

pub fn find_filesystem_workspace_root(start: &Path) -> Option<PathBuf>

Compatibility alias for find_workspace_root — kept so existing CLI subcommands (export, changes, …) that historically routed through the lean-flavour walker continue to compile. Both walkers now find the same marker; the alias is intentional for call-site clarity (find_workspace_root reads as the canonical surface; find_filesystem_workspace_root documents the folder-mount-only intent of its caller).