@aegiskit/policy-diff

Semantic access diff for Supabase RLS migrations: compare the access-control surface (policies, RLS state, table grants) of two migration states and get, in plain language, who can newly read or write what — for PR review, CI gating, and change-management evidence.

Install

pnpm add @aegiskit/policy-diff @aegiskit/scanner

@aegiskit/scanner is a peer — it supplies buildRlsModel and SqlSource. Most users get this wired for free via the aegis diff CLI and the GitHub Action; import this package directly only to build a custom gate.

import { buildRlsModel } from '@aegiskit/scanner';
import { diffAccess, renderDeltaMarkdown, summarizeDeltas } from '@aegiskit/policy-diff';

const base = buildRlsModel(baseSources); // supabase/migrations/**.sql at the base ref
const head = buildRlsModel(headSources); // …at the head ref

const deltas = diffAccess(base, head, { trustedFunctions: ['public.is_member'] });
console.log(renderDeltaMarkdown(deltas, { baseRef: 'main', headRef: 'feat/x' }));
summarizeDeltas(deltas).conclusion; // 'no-change' | 'neutral' | 'attention' | 'action-required'

Trust contract

• widening is claimed only when the after-rows are a superset-or-equal of the before-rows under the class lattice (none ⊂ own/state/delegated ⊂ all).
• narrowing only when they are a subset-or-equal — a "safe" verdict never papers over a possible widening.
• Everything unverifiable — custom functions off the trustedFunctions allowlist, incomparable class moves (owner-scope ↔ row-state ↔ membership check), statements the model recorded as uninterpreted (NO FORCE, partial REVOKE, policies on unmodeled schemas, exotic quoting) — is requires-review. The diff fails closed: it may ask a human to look, it never says "no change" when it cannot know.

Honest scope

This reasons about the shape of predicates over repo-managed SQL. It does not know your data model or business rules, does not see policies changed outside migrations (e.g. via the Supabase dashboard), and a clean diff means "no access-relevant change detected in the modeled surface" — never "this migration is safe". It complements review; it does not replace it.