Function start_config_watch 

fn start_config_watch<F>(workspace: &Arc<Workspace>, apply: F)
where
    F: Fn(&Workspace) + Send + Sync + 'static,

Watch forge.toml for the process’s life and apply each valid edit.

The watch is a single file (forge.toml), never the config directory, so nothing else in that tree can trigger a reload. Each event is a whole-file read: a rejected file leaves the previous config live and logs one WARN, and an applied one logs the tables that moved and the keys that only a restart can take. apply runs for the subsystems the boot holds.