control:  DF2502 bzero(len=512)
hostile:  DF2502 bzero(len=18446744071562067968)     <- 0xffffffff80000000, sign-extended INT_MIN
          (subsequent rig-state crash at 0x64(%rcx) occurs in BOTH runs - rig artifact, not the defect)
--- fixed source A/B ---
dmesg | grep -c "DF2502 bzero" -> 0        <- no bzero issued; run completes, guest survives