GitHub Copilot App Canvas is designed for shaping and validating agent-driven software systems during development, not for building user interfaces. Traditional UIs are for end-users interacting with finished products, whereas Canvas is for developers and AI agents actively building and evolving systems. It provides a surface for agent observability, fault injection, live state mutation, and validation feedback, acting as a crucial debugger for agent-driven solutions.A customer support triage system scenario demonstrates Canvas's capabilities, involving five specialist agents: decomposer, executor, validator, designer, and tracker. Actions on Canvas can be triggered by humans or AI, allowing for collaborative development. The system's state mutates and streams back to the UI in real-time.The development process on Canvas follows five beats: decomposing requirements into task flows, executing these flows by coordinating agents, validating performance against defined criteria, injecting failures to test adaptability, and evolving the design live based on validation results. This iterative loop allows for immediate feedback and adjustments.This scenario proves that Canvas makes end-to-end design visible, allowing developers to observe multi-agent collaboration and test fault tolerance. It enables validation-driven iteration, transforming the development process from writing static code to orchestrating and continuously evolving living systems. Canvas facilitates a shared runtime where human and AI participants co-create, observe, and shape agent systems together, accelerating innovation.