Build-Loop — see-and-exercise iteration until a build actually works

Drive a build to actually-works, near-finish-line craft by looping build → see → exercise → check → critique → rebuild over the agent's existing tools (bash build/test, headless screenshot + vision, Playwright, axe/Lighthouse) until acceptance criteria pass or an explicit stop-condition fires — no infinite thrash. ALWAYS invoke when the user says any of "tighten this build", "iterate until it passes", "self-verify the UI", "make it actually work, not just compile", "loop until the core flows pass", or "drive this to near-finish-line". Also invoke proactively after a scaffold or feature lands and before handing a draft to a human. Composition-first over existing tools, not…