Build pipeline and .oxbin

An Argon workspace compiles to one content-addressed file: .oxbin. This chapter is the build contract: what ox build accepts and rejects (ox build is fail-closed), the pipeline that produces the artifact (Pipeline), how a composition gets its cryptographic identity (Composition signature), the artifact’s section model (Section model), versioning (Versioning — four orthogonal axes), content-addressing (Content-addressing), and load-time validation (Load-time validation — two layers). The byte-level wire format is documented in the oxc-oxbin crate (compiler/crates/oxc-oxbin/FORMAT.md); the axiom-ADT body variants the events section carries are catalogued in Axiom-ADT variant catalog.