pub fn slot_session_from_stem(stem: &str) -> Option<&str>Expand description
Recover the session id from a slot file stem ({model_id}__{session}).
Splits on the first __. Model ids are numeric and contain no __, so
the first __ is always the model/session delimiter — this correctly
recovers the session even when the session id itself contains __.
Returns None for a stem with no __ (e.g. a legacy pre-namespacing file),
which callers treat as “not one of our namespaced files”.