Grammar: opcode rule now accepts param_ref alternative, positional_arg accepts OPCODE token. Lower pass defers ParamRef opcodes and wraps bare OPCODE tokens in macro call arguments as strings. Expand pass resolves opcode mnemonic strings to ALUOp/MemOp via MNEMONIC_TO_OP during macro body cloning. Enables: #reduce_2 op |> { &r <| ${op} } / #reduce_2 add