Function forecast_keep_purge 

pub fn forecast_keep_purge(parent: &Path, keep_cap: usize) -> usize

Forecast how many session directories the next new session would auto-purge under parent given the current keep cap. Returns 0 when no purge would happen (or when keep_cap == 0, which disables the cap).

Logged at INFO level by the end-of-run notice guard so operators see the imminent cleanup before it happens, with instructions for disabling it.