Authentication and payment flows are proven and contract-sensitive. Platform refactoring must not break existing integrations. Freeze behavior and contracts for authentication flow, payment API interactions, and authorization logic. Allow only encapsulation and integration-layer isolation, not contract redesign.
This decision remains in effect. The full, verified contract — the Telegram QR/session flow, cookie policy, the frozen payment endpoint shapes, and the still-unresolved admin-authorization gap this ADR's constraint interacts with — lives in `docs/backend/BACKEND-INTEGRATION.md` §2 and §2.5–§2.8. Read that document for current, code-verified detail; this file is kept only so ADR-numbered references in `docs/architecture/foundation/README.md` continue to resolve.
