When true, the handler computes and returns the would-be deletion count (deleted) without writing anything — the preview side of a preview-then-confirm flow. When omitted or false, matching memories are soft-deleted immediately.

Phase 10.7 — right-to-be-forgotten. When true, the handler also removes the supersession history (rows with valid_until set) that match the same scope/entity criteria. When omitted or false, prior rows are retained for audit even after the current row is soft-deleted.