overrun iff (160 + 4*n) % 256 == 0 iff n % 64 == 24
== fixed accounting (emit_frame_size += 2 for TMZ) ==
fixed: 0 overrun submission(s) in num_ibs 1..200 (expect 0)
VERDICT: baseline overruns by exactly 2 dwords iff num_ibs % 64 == 24; fix eliminates all. REPLICATED.