Design Blueprint: Postcode Capacity Check

Design blueprint derived from the source paper (DOI 10.5281/zenodo.24121736): A local postal code introduced for one settlement must do three jobs: name every household, leave room to grow, and betray its own copying errors. This paper sizes the code for a settlement of 8500 households with a stated growth factor of 1.8 over the planning horizon and a quarter of the code space held in reserve: 20400 codes are required, so 5 digits — capacity 100000, a headroom of 4.9 times — plus one check character, for a total length of 6. The check character, a weighted mod-11 sum, was verified by exhaustive testing rather than asserted: all 180000 single-digit errors in the test set 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.