EEF-CVE-2026-82745

ETS and Mnesia data layers overwrite an existing record on create instead of enforcing primary-key uniqueness

## Summary Improper Access Control vulnerability in ash-project ash lets a create action overwrite an existing record when the ETS or Mnesia data layer is used, because neither enforced primary-key uniqueness on insert. Unlike a SQL data layer, whose unique primary-key constraint rejects a duplicate, the ETS and Mnesia data layers implemented `create` as a keyed insert that replaces any existing entry with the same primary key (`lib/ash/data_layer/ets/ets.ex`, `lib/ash/data_layer/mnesia/mnesia.ex`). An actor who can set the primary key on a create (for example a user-supplied string or integer key) can submit a create whose key matches an existing record and silently overwrite it, destroying and replacing another entity's data without going through the update action or its policies. The fix rejects a create whose primary key already exists with an already-taken error, and only allows duplicates for keyless resources. This issue affects ash: from 0.4.0 before 3.32.2.