Electrocatalytic urea synthesis from CO2 and NO3– offers a sustainable alternative to energy-intensive industrial methods, yet precise C–N coupling remains hindered by kinetic mismatches between the reduction reactions. Here, we report a strategy leveraging programmable Zn-node gasification to thermally sculpt 1.5–1.8 nm cavities within zeolitic imidazolate frameworks, hosting atomically dispersed Cu–N4 sites. Thermal transformation retains macroscopic framework, creating size-matched nanoconfined environments for selective catalysis. An optimal confinement metric descriptor (9.64) is introduced as a predictive design parameter, correlating cavity geometry with local electric field and Cu d-band modulation. This design stabilizes *CO and *NO intermediates, effectively suppressing parasitic reactions and lowering C–N coupling barriers. Consequently, the catalyst delivers a record urea yield of 71.32 g gcat–1 h–1 with 98.9% Faradaic efficiency in gas diffusion cells. Pilot-scale testing confirms its stability over 300 h, establishing nanoconfinement as a pivotal design principle for high-performance urea electrosynthesis.