feat(app-shell): CEL authoring safety for RLS policies — lint, field autocomplete, test-run #2413

Context

The permission-set Studio editor (PermissionAdvancedFacets — the Row-Level Security section) lets admins author RLS policies as hand-typed CEL USING (read filter) and CHECK (write filter) expressions. A rich set is edited entirely by hand — e.g. member_default has 17 policies, each with per-operation USING/CHECK editors.

Problem

The CEL editors today have no syntax validation, no field-name autocomplete, and no way to test a policy.

RLS is a security-critical surface: a typo in a USING/CHECK predicate silently produces the wrong row scope, and some evaluation paths fail open — so a mistake widens access with no visible error. This is the highest-risk, most error-prone authoring surface in the permission model, yet it has the least authoring support.

Proposed work

1. Client-side CEL syntax lint — surface parse errors inline before save (reuse the framework CEL parser rather than maintaining a second grammar).
2. Field-name autocomplete — while typing, offer the target object's fields plus the scope vars (current_user, record, ctx, app, …) to prevent silent typos on unknown identifiers.
3. Test-run affordance — "evaluate this policy against a sample record" so the author sees allow/deny before shipping.
4. Optionally, flag where a policy fails open vs. fails closed so authors understand the blast radius of a malformed predicate.

Acceptance criteria

• Malformed CEL is flagged inline and (optionally) blocks save.
• Autocomplete suggests valid field/scope identifiers for the policy's object.
• An author can dry-run a USING/CHECK predicate against a sample record and see the result.

References

• Editor: packages/app-shell/src/views/metadata-admin/PermissionAdvancedFacets.tsx (RLS section)
• CEL evaluation: ExpressionEvaluator (@object-ui/core); framework CEL parser
• Part of the permission-set pure-model work — epic Epic: Permission sets — Studio designs every facet, Setup assigns users (ADR-0056) #2398

Surfaced during go-live UAT while verifying the Studio RLS editor (P3).