The Implementation Codex

AI-assisted software construction is highly sensitive to underspecified dependencies, interfaces, invariants, tooling, and acceptance criteria. The Implementation Codex is a proposed realization package that binds a system specification to dependency structure, build phases, reusable patterns, language and environment bindings, verification gates, authority, evidence, and a refinement journal. The source reports eight sequential builds across Python and TypeScript using two model classes. Those builds are a valuable case study, but they do not yet demonstrate deterministic realization, executor or language independence, or that correctness resides in the specification. Codex versions, environments, test counts, and interventions changed; some table entries report final green status rather than first-pass status; the same models were not always evaluated on the same version; and zero new observations can mean saturation, weak observation, or both. This revision treats implementation as a relation among specification, configuration, executor, tools, environment, realization, verification, and evidence. It defines a Codex envelope, distinguishes conformance from correctness and first-pass gate success, expands failure attribution, places the method at the IC-to-IR segment of the realization funnel, and specifies an independent held-out validation program. The defensible thesis is that a sufficiently explicit, verified Codex may reduce executor discretion and implementation rework within a declared profile.