Plans a day hike leg by leg. Estimates time with Naismith's rule and Langmuir's descent corrections, adjusted for terrain, fitness, pack weight and breaks, gives clock times for each leg, checks the finish against sunset and the latest safe start, and works out water to carry between refills and snacks to pack. Flags after-dark finishes, long dry stretches and hard terrain late in the day. Includes a stdlib Python planner with --self-test.
