ADR-0087 exemption (no-migration-prescription): A validity narrowing over existing keys: no key is removed, renamed or re-shaped, so there is no tombstone and nothing mechanical for `objectstack migrate meta` to rewrite. The refusal reaches an affected author at the parse/query site carrying the remedy; which explicit spelling matches the author's intent ($or with $null:true, $null:false, or a half-open range) is an authoring decision no migration entry can perform — and the ruling's evidence base measured zero authored occurrences of the refused shape.