Electrosynthesis of organic amino acids from inorganic nitrogen feedstocks offers a new route to expand the synthetic boundaries of biologically relevant C–N molecules. However, the desired organic C–N coupling pathway is kinetically suppressed by the competing inorganic ammonia (NH₃) pathway, rendering selective amino acid electrosynthesis intrinsically challenging. Here, we uncover that this bottleneck originates from the uncontrollable gatekeeping intermediate, hydroxylamine (*NH₂OH), at the decisive branching point. To address this challenge, we develop a new programmable reaction-network bifurcation (PRNB) strategy, enabled by an atomically precise dual-site metallene, which directs the reaction bifurcation of *NH₂OH from hydrogenation to C–N coupling. As a result, the system reverses the product selectivity, allowing the coupling product to outperform NH₃ by a factor of 28.5. This shift further achieves glycine synthesis with a high Faradaic efficiency of 83.2% and a formation rate exceeding 885 mmol/g_cat/h, sustained over 225 h and enabling gram-scale synthesis. Mechanistic studies reveal that dual sites reprogram the relative bonding preference of *NH₂OH, making C–N coupling dominant for oxime formation. In situ spectroscopy and kinetic isotope measurements further reveal that dual sites reorganize an ordered interfacial H₂O network that lowers the hydrogen-transfer barrier by more than half, enabling rapid oxime hydrogenation and high-rate glycine production. The efficient synthesis of diverse amino acids, including alanine, glutamate, and leucine, further underscores PRNB as a general paradigm for controlling reaction-network bifurcations in complex chemical synthesis.