Collect every stable_id across the given lessons and report duplicates with their locations. Elements without a stable_id are skipped (the field is optional); total is the checked quantity so a run over nothing stays visible to the caller.
total
Collect every stable_id across the given lessons and report duplicates with their locations. Elements without a stable_id are skipped (the field is optional);
totalis the checked quantity so a run over nothing stays visible to the caller.