Holds everything web, mobile and API must agree on: DTOs, zod input schemas, plan entitlements (the single place feature gates live), streaming-service link helpers, feed ordering and a typed API client. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8