- Add packages/auth/src/seal.ts: shared AES-256-GCM seal/unseal using BETTER_AUTH_SECRET - Export seal/unseal from @mosaicstack/auth index - Refactor provider-credentials.service.ts to import seal/unseal from @mosaicstack/auth - Add apps/gateway/src/federation/peer-key.util.ts: sealClientKey/unsealClientKey wrappers - Add peer-key.spec.ts with 5 vitest tests (round-trip, non-determinism, at-rest, tamper, missing secret) - Document key rotation deferred procedure in docs/federation/SETUP.md Co-Authored-By: Claude Sonnet 4.6 <[email protected]>