Reflex: an architecture for building mobile apps with agents

In Native is now the future of mobile at Shopify, we explained why we're moving back to Swift and Kotlin, and in Helix we shared how agents rebuild screens through small checkpoints and strict gates. Both posts mention a CLI that lets an agent inspect the app's state and run actions without a simulator. This post is about the architecture behind it, which we call Reflex. When we decided to rebuild our apps natively, we went back to the drawing board with a basic question: how should a mobile app be built when agents write most of the code? The biggest bottleneck we had was the feedback loop. An agent can write a screen in minutes, but proving that the screen works requires an emulator, a build, a tap script, and a lot of patience. We had invested in simulator tooling to speed that up and hit a ceiling on how fast it could get. Reflex is what emerged. The app's logic runs headlessly, every screen exposes its state and actions through one small contract, and a CLI drives that contract on both platforms from the same test file. This unlocked extremely fast feedback loops and gave us a way…