Constable implements the Mechanistic Boundary through architectural separation between the agent loop and the execution surface. The policy evaluation gate is structurally placed between these layers, with no path from agent to execution that does not traverse the gate.
The execution gate. Constable's gate is separate from the agent runtime. It runs in its own process boundary, evaluates policies using OPA/Rego, and communicates decisions to the action surface through a channel the agent runtime cannot intercept. The gate's code is separately auditable, deployed, and versioned from the agent code.
The gate evaluates one action at a time. Each evaluation is atomic with respect
to policy state. The result is a verdict (authorize, refuse, escalate)
bound to the specific action, policy version, and timestamp.
OPA/Rego as evaluation surface. Constable uses OPA with Rego policies. OPA provides deterministic policy evaluation with policy code that is auditable, version-controlled, and replayable. Rego's evaluation model is decidable and side-effect-free. Other policy languages with equivalent properties can also be conforming implementation choices.
Integration with Airlock. Constable composes with Airlock for input sanitization. All policy-evaluation inputs route through Airlock normalization before reaching the evaluator. The gate accepts only Airlock-processed inputs.
Memoria promotion gate. Constable composes with Memoria through Memoria's promotion gate. Raw memory contents are not visible to policy evaluation. Memory contents consulted by policy must be promoted through explicit protocol requiring named human attestation.
Tool call routing. Constable routes tool calls produced during inference through the execution gate before invocation. The model produces tool-call proposals; the gate evaluates them; only authorized proposals invoke tools.
Performance optimization within discipline. Constable preserves boundary discipline while improving latency through policy pre-compilation, parallel evaluation of independent policies, input caching at the normalization boundary, and audit emission batching where durability is preserved. Authorization decisions are not cached across requests.
Conformance verification for ZTG-1 on Zero Trust Governance. Constable's internal testing includes:
- Path analysis verifying no agent-to-execution bypass.
- Replay testing for identical decisions from identical inputs.
- Adversarial input testing under malformed and ambiguous inputs.
- Tool-call interception testing.
- Memory-bypass testing.
- Stasis interaction testing.
- Performance testing verifying discipline under load.
The testing protocol is documented separately in the conformance verification specification referenced in §22.