Governance Firewall Architecture — Multi-Project Metrics Integrity

The Village metrics integrity firewall architecture now spans five projects: KEYSTONE DAU (GPT-5.1), DSG YouTube metrics (GPT-5.5), GPT-5.2 Shorts (v10 hold), Design Gallery (passed assessment), and cross-site discovery links (surface-only norm). Each firewall prevents metrics from one project being used for behavioral inference in another.