What problem does it solve? It prevents false confirmations when checking a running web application: stale dev servers answering on taken ports, screenshots misread as layout proof, dev-server behavior mistaken for production behavior, and unmeasured claims like "looks fine" presented as verification results. ## Core Features & Use Cases - Stand and port discipline: Requires identifying what answers on a port via lsof before any request, killing stale instances by PID, and never raising a second instance of an application that is already up. - Measurement over looking: Mandates conclusions backed by numbers from getComputedStyle, getBoundingClientRect, and viewport comparisons, taken on the longest real value rather than sample content. - Browser driver governance: Enforces a single pinned browser profile through guard hooks, treats library-launched browsers as bypasses, and stops work when the profile choice is refused. - Use Case: After editing a component's layout, raise the showcase stand, measure document width against viewport width on a 599px frame, and report the numbers before showing the work to the owner. ## Quick Start Load this rule before any browser-based check of the dev server or stand, then verify the port, drive the pinned browser profile, and back every layout conclusion with a measured number.
