Trust, Accountability and Control: Post-Quantum Authentication and Evidence-Driven Authorization for Artificial Intelligence Agents

Artificial intelligence (AI) agents need authenticated identities, bounded action scopes and evidence before receiving adaptive authority. We present a post-quantum trust, accountability and control (TAC) protocol composing signed requests, independently signed observations, scoped admission and transactional evidence consumption. A Tamarin abstraction checks six universal receipt properties and two existential witnesses; three mutants expose omitted mechanisms. Replay preserves 38,400 recorded controller positions. Execution study E6 covers 48 matched configurations and eight ablations: the bound dispatcher produces no unpermitted effect in 22 mediated configurations, while both privileged bypasses succeed. Twelve-visit study E7 compares adaptive authority with competent static enforcement in 28 matched episodes, alongside 24 isolated execution ablations and two history-mutant diagnostics. Both policies resist tested command substitutions; adaptive warm-up withholds 24 of 48 compliant proposals. False authorized reports violate the illustrative task predicate under both. Two diagnostics show signed-prefix reconstruction detecting injected duplicate reinforcement before effects, and a separate arithmetic oracle checks retained trajectories. Paired-path medians are 3.41 ms for the module-lattice-based digital signature algorithm ML-DSA-44 and 2.19 ms for Ed25519 on the recorded x86 configuration; separate primitive experiments examine build sensitivity. Deterministic results establish conditional composition boundaries with progress costs. Truthful observation, complete mediation, provisioning and durable storage remain assumptions.