EEF-CVE-2026-78230

## Summary

AshAi exposes Ash read actions to language-model tool calls. The read tool accepts an aggregate result type (`min`, `max`, `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 tool caller could therefore read a field the calling actor's field policies forbid by requesting it as an aggregate; `min`/`max` in particular return an actual field value. This includes fields that are `public? true` but restricted per-actor by a field policy, such as sensitive PII. The tool's existing check only required the field to be public, 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_ai: from 0.1.0 before 1.0.3.

## Configurations

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