Add InteractionForm::for_handle so tests and public integration code can construct dispatched forms from generated Handle<T> values instead of raw numeric handle ids.
req: ceremony/004
req: public_api/001
Add HandlerRegistry::register_handle for generated Handle<T> values and migrate examples away from passing raw numeric handle ids at registration sites.
req: ceremony/004
req: public_api/001
Cover the integration boundary for CSRF-style hidden fields: InteractionForm keeps arbitrary form fields available to app/auth extractors instead of dropping them during dispatch parsing.
req: auth/004