The Constitutional Codex

The Implementation Codex (CX-I) demonstrated that software construction can be made deterministic through phase-gated, AI-executable specification. But implementation correctness is only one layer of a complete system specification. The Implementation Codex tells an agent how to build a system -- it does not explain why this configuration was chosen, what alternatives exist, or what would need to change if requirements shifted. This paper introduces the Constitutional Codex (CX:AES): a three-layer specification framework that extends the Implementation Codex with two additional layers -- the Constitutional Specification (CX-S), which defines the field of possibility and domain constraints, and the Constitutional Configuration (CX-C), which documents the selected design, its rationale, and the topology of alternative configurations. Together, the three layers form a complete, corrigible, agent-executable specification: the CX-S declares what could be built, the CX-C declares what was chosen and why, and the CX-I declares how to build it. All three layers are updateable through observation and insight, using the same journal-driven refinement cycle that proved effective for the Implementation Codex. The central claim is: a system is fully specified only when its possibility space, configuration rationale, and construction plan are all explicit, all corrigible, and all agent-executable.