X_ACTION_DEPRECATION_INVALID
Means
an action declares a deprecation whose dates cannot be rendered
Typical cause
a deprecated: { since, sunset } value that is not a date. Refused where the declaration is converted, so the route and the OpenAPI operation refuse the same value — a Sunset header rendering Invalid Date is a contract statement no client can act on
Fix
edit deprecated: { <field>: … } on the action to an ISO-8601 instant — e.g. '2026-12-31T23:59:59Z'