KOS_OP_FAST_INPLACE

• Style: EXTRA (OPERAND, FASTVAR). Row a0 = the bare KosOperand selector; a1 = fast slot index.

• Stack: [..., rhs] → [...]. Augmented assignment on a fast slot: obj = deref(slot); obj OP= rhs; store back. No value pushed.

• Compiler form: Post-compile only: the convert_fast lowering of VAR_INPLACE.