KOS_OP_FAST_CLEAR3

• Style: EXTRA (FASTVAR, FASTVAR, FASTVAR, NOARG). Row = 3 fast slot indices (post-compile).

• Stack: No stack effect. Clear the 3 fast slots in row order, as 3 FAST_CLEAR would; an already empty one stays empty.

• Compiler form: Never emitted by specials. Produced only by ByteCodeProcessor.pack_runs, which combines a run of consecutive FAST_CLEAR rows (quads first, then one triple or one pair).