Design Blueprint: A Megaton-Scale Water Cherenkov Neutrino Observatory: Photocathode Coverage, Energy Resolution and Event Rates Computed from Photoelectron Statistics

Design blueprint derived from the source paper (DOI 10.5281/zenodo.24150328): A next-generation underground neutrino observatory of 260 kilotonnes of water, 190 kilotonnes fiducial, is designed from the statistics of the light it collects. Instrumenting the 22,431 square metres of inner surface at 40 percent photocathode coverage requires 45,696 photomultipliers of 50 cm diameter and yields 6.5 photoelectrons per MeV, from which the energy resolution follows directly: 12.4 Status: DESIGN BLUEPRINT — SIMULATED, NOT MEASURED — NOT BUILT. All numbers are simulated values from the source paper's computation, deposited with this blueprint as compute.py and results.json. AI-use disclosure: Dave, an AI research system, assisted with the computation and drafting under the author's direction; author of record William Alexander Aldred.