I've been heads-down for the last few months on Deroom AI , an AI room design tool that turns a single photo of your real room into a photorealistic redesign in 30 seconds. The 0→1 build was way harder than I expected and along the way I changed my mind about a bunch of things. These are the four that cost me the most time. 1. Generic image generation is the wrong primitive The first version was a thin wrapper around a stable-diffusion checkpoint with a prompt template. It produced beautiful kitchens. They just weren't your kitchen. Walls moved. Windows shifted. Cabinets rearranged themselves. That's useless if the entire reason a homeowner is on the site is to decide whether to repaint their existing cabinets sage green or off-white. The fix took weeks: switch to a controlnet-driven pipeline that uses the input photo as a structural reference. Footprint, plumbing, doors, windows, ceiling height — locked. Only finish changes (paint, tile, cabinetry, lighting, soft furnishings).…