EEF-CVE-2026-78216

## Summary

AshLua exposes Ash read actions to Lua scripts run through an `eval` action. A read call accepts an `operation` (`list`, `min`, `max`, `first`, `sum`, `avg`) that builds an ad-hoc `Ash.Query.Aggregate` over a named field and returns its raw value.

Ash field policies redact forbidden fields on returned records (replacing them with `%Ash.ForbiddenField{}`), but that redaction does not apply to aggregate values. A script could therefore read a field the calling actor's field policies forbid by requesting it as an aggregate instead of as a field. This includes fields that are `public? true` but restricted per-actor by a field policy, such as sensitive PII. The prior hardening only enforced the exposed-field allow-list (field visibility), which is a separate axis from per-actor field-policy authorization.

The fix authorizes the aggregated field against the resource's field policies, so aggregating over a field the actor may not see is refused or scoped to the rows where it is visible.

This issue affects ash_lua: from 0.1.0 before 0.2.2.

## Configurations

Reachable only when an application exposes an AshLua `eval` action over a resource whose field policies restrict a field that the calling actor can still name as an operation aggregate (for example a `public? true` but field-policy-protected attribute).