ADR-0087 exemption (no-migration-prescription): An accept-set narrowing on a LOADER, not on any authorable key: no property of any spec schema is removed, renamed or re-shaped, so there is no tombstone and nothing for `objectstack migrate meta` to rewrite in a stored document. The affected artifact is a FILESYSTEM LAYOUT — two sibling files — which the ledger cannot address at all: a migration entry rewrites metadata bodies, and neither of the colliding files is wrong on its own. Which one an author wants kept is intent no entry can decide: they may have meant the conversion to `.yaml` to land and forgotten to delete the `.json`, or may have meant the opposite, and the two files carry no evidence of which. The refusal is the channel that reaches them, at the load site, naming both paths, the type, and the remedy. Measured in-repo population of affected trees is zero: a walk of 7,770 tracked files over 526 directories found no directory holding two files with one stem among the registered extensions, and there are no `.yaml`/`.yml` metadata files outside CI and workspace config.