APR-Lite Phase 6 Technical Note: Coalition Drift and Cross-Agent Memory Governance in Regulated Multi-Agent AI Systems

This technical note describes Phase 6.0 of the APR-Lite governance platform: Coalition Drift and Cross-Agent Memory. Phase 6.0 introduces two governance surfaces not present in prior phases. Coalition drift detects governance patterns that only emerge when examining multiple agents collectively — drift that is invisible at the individual agent level but visible across the coalition. Cross-agent memory governs memory sharing between agents in a coalition under explicit policy, without collapsing into an unbounded shared memory pool. Both surfaces are implicit: they run inside existing routes (session/step, routing/resolve, memory/retrieve) with no new public endpoints. A new CRITICAL severity tier is introduced, representing coalition-level freeze. The implementation is validated against a 16-test smoke suite. Phase 6.1 (cross-session coalition patterns and observability endpoints) is deferred.