9004 Shared Dtos In Common Package

Request and response DTOs shared across clients were duplicated per client, drifting over time and breaking the version matrix (server must support clients up to two major versions behind).

Decision

Cross-client DTOs live in a single shared common package. New fields on existing DTOs are optional, so a client that has not updated still deserializes responses. Required fields are never added to an existing shared DTO.

Consequences

• One source of truth for shared contracts.
• Adding a required field to an existing shared DTO, or forking a per-client copy of a shared DTO, is a deviation from this decision.