This technical note defines Semantic Compilation Architecture as the Phase-2 theory of the AIKernel / AIOS paper series. It explains how the static boundaries defined in Phase-1 become a semantic runtime theory of observable semantic state, governed transition, runtime policy, and deterministic synthesis. The paper introduces Semantic IR as a four-slot representation aligned with the Phase-1 papers: graph topology, capability types, governance constraints, and boundary invariants. It further defines Governed Circuits, Prototype Space, Semantic Compression, composite distance evaluation, Runtime Policy, and deterministic structural synthesis under fixed mappings. This work generalizes Paper 04, Trajectory Governance Model, from an operational governance algorithm into a broader semantic runtime theory. It also positions Phase-3 as a future foundation layer for identity, provenance, cryptographic addressability, digital deeds, and trust-oriented AIOS extensions. The English manuscript is the canonical version. The Japanese manuscript is included as a companion translation.