Arcstone Systems Architecture Specification: Deterministic Deployment of an Autonomous AI Agent in a High-Consequence Environment

Document Reference: ARC-SPEC-AGENT-HCE-001 Governing Framework: Invariant Taxonomy (Physical, Digital, Legacy) Primary Invariants: Δ_external = 0; τ_override ≤ 11.99 ms (11,990 µs); S_max ≤ 4096 B Target Master Anchor: A-77-DELTA-SHIELD-LOCKED (10.5281/zenodo.22665852) This systems architecture specification defines how to deploy a non-deterministic producer (an LLM or agentic reasoning framework) in high-consequence environments without permitting it to hold ambient authority over external system state. It treats the agent as an untrusted, high-entropy proposal generator whose candidate actions must traverse an independent, deterministic #![no_std] Rust admissibility gate and Aya eBPF LSM/tc kernel classifiers before state mutation is permitted. Key Contributions: 3-Tier Invariant Taxonomy: Assigns all controls strictly across Physical (STO relays, mechanical end-stops), Digital (#![no_std] Rust gate, eBPF LSM/tc classifiers), and Legacy (prompts, LLM judges) tiers. Lattice Join Supremum Rule: Proves that Legacy controls can only raise verdict severity (e.g., PASS to REFUSAL) but can never lower a Digital DENY to PASS. Concrete ABI & Memory Layout: Defines the fixed-width C++20/Rust ActionDescriptor memory layout (S_max ≤ 4096 B) and 5-tier poset verdict mapping (POSIX 0, 10, 12, 30, 32, 40). Microsecond Preemption Budget: Allocates the parallel fan-out override timing budget (τ_override ≤ 11.99 ms) across detection, latching, tc egress drops, cgroup freezing, and STO hardware relay dropout.