Design Blueprint: Three Hundred Millimetres of What? Ponding Depth Set by Soil Drawdown, Not by the Standard Detail

Design blueprint derived from the source paper (DOI 10.5281/zenodo.24119678): Rain gardens are commonly detailed with a standard ponding depth — 300 mm appears in guide after guide — as if the depth were a property of the garden rather than of the soil beneath it. 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.