ADR-0087 exemption (already-registered): the registered entry carries this family's hand-migration, an aggregate the field accepts with count as the one that stays for a JSON-stored field, and the count_distinct narrowing over the JSON-stored types already rides it. A select, radio, lookup, user, file or image field declared multiple: true is the one JSON-stored shape the per-type table cannot see; the dataset compile leg and the engine's count_distinct door refuse it beside the table's row, and this is the authoring leg of that same pair, so it adds no surface of its own.

ADR-0087 exemption (no-migration-prescription): a refusal of a grouping TARGET at authoring time: a dataset dimensions entry whose field resolves to a declared structured-JSON field (json, composite, repeater, record, location, address, vector) or multi-value field (multiselect, checkboxes, tags, or a select, radio, lookup, user, file or image declared multiple: true). It is the authoring leg of the analytics door that already refuses every query grouping by such a column with 400 INVALID_FIELD, and that door's own changeset declared this category for this surface. No authorable key, spelling, export or stored shape moves: DatasetSchema keeps parsing every dimension, no stored row is read or rewritten, and which scalar part of a document, or which member of a list, an author meant to group on is not something a ledger entry can rewrite. The other categories are closed on facts: the package publishes (not unpublished); no ADR-0087 id covers a grouping target, and dataset-measure-aggregate-field-type-refused says in its own reason that a field used as a DIMENSION is untouched (not already-registered); and the change is a rule verdict, not a declaration (not runtime-interface-only or type-surface-only).