Function ensure_runtime_temp_dir 

pub async fn ensure_runtime_temp_dir(temp_root: &str) -> Result<String>

Ensures the short-lived runtime temporary directory exists.

The directory is derived from [aster_forge_utils::paths::runtime_temp_dir], so all Aster services use the same _runtime namespace under their configured temporary root. Products keep ownership of when the directory is cleaned and how IO errors are mapped into their own error types.