E2E Behavior Validation for Frontend Modifications Core Principle: Test Product Behavior, Not UI States CRITICAL : Tests must verify that product features WORK correctly, not just that UI elements render. What NOT to test (UI States): - ❌ "Dropdown opens when clicked" - ❌ "Modal appears after button click" - ❌ "Loading spinner shows during request" - ❌ "Form fields are visible" - ❌ "Sidebar collapses" What TO test (Product Behavior): - ✅ "Selecting an LLM provider configures the agent to use that provider" - ✅ "Creating a new agent persists it and shows in the agents list" - ✅ "Running a tool…