Works out how much paint to buy for one or more rooms and what it will cost. Measures walls (minus doors and windows) and ceilings, applies coats, coverage, texture and waste, adds up each paint across rooms, and picks the cheapest can mix with little left over. Flags dark-to-light changes and new plaster that need primer, one-coat plans, suspicious coverage or heights and big leftovers. Includes a stdlib Python estimator with --self-test.
