Preserve explicit model and provider architecture (#30)

frontend/AGENTS.md

@@ -12,6 +12,13 @@ skill to perform this completion workflow.
 
 ## Preserve the frontend architecture
 
+This applies to `frontend/app`, every shared package and future web/mobile
+clients, including in-memory stubs. Keep an explicit data model even when it
+currently resembles the DTO; do not use a provider as a substitute for that model.
+The UI depends on providers/models; providers depend on service contracts; service
+implementations own DTO conversion through mappers. Replacing a service must not
+require DTO or networking changes in widgets or providers.
+
 - Strictly preserve the existing `dto` -> `mapper` -> `service` -> `model` ->
   `provider` flow. Widgets consume models and provider state; they must not
   bypass the flow by parsing transport data or calling backend APIs directly.