Function label_selector_string 

pub fn label_selector_string(sel: &LabelSelector) -> String

Render a LabelSelector as the API server’s selector string.

Lives here so the controller and the CLI build byte-identical queries: a divergence would make kubectl kopiur snapshot now and the schedule expand to DIFFERENT PVC sets for the same recipe, which is the kind of discrepancy nobody notices until a restore is missing a volume.