RFC-0031: Component ABI

Status: Normative — frozen. Component descriptor is (ComponentTypeId,SchemaHash,u32 abi_major,u32 flags,u32 value_size,u32 value_align). ABI bytes are canonical schema values, never native structs. value_align is power-of-two ≤64; fixed-size descriptors must match schema size. Calls pass descriptor plus (ptr,len) and validate type/schema/length before read. ABI major mismatch or unknown required flag fails; minor compatible additions use new descriptor flags only. Mutable access requires RFC-0033 Write capability and RFC-0023 transaction.