Constant MAX_DISTINCT_IDS 

pub const MAX_DISTINCT_IDS: usize = 100_000;

Per-call cap on the bounded HashSet<Id> used by Collection::count_distinct_ids_in_range to count unique document Ids under an Each index. Power-of-ten Rule 3: the distinct set is allocation-bounded; exceeding the cap surfaces obj_core::Error::DistinctCountExceeded rather than chewing arbitrary memory. The user can narrow the range via .index_range(...) to fit inside the budget.