STUB: Specifies the C ABI that language bindings are written against: the ABI version and the rule for when it changes, the error-reporting convention every fallible function follows, and memory ownership across the boundary. Lists the binding-facing types and functions in collapsible tables grouped by purpose: shared memory, schemas, packing and unpacking, packets, Arrow, caching, intrinsics, and utilities. Functions used only by the nexus are out of scope.