== DF-2399 baseline (ACHARNESS #3, agp_shim verbatim agp_open/agp_close) ==
AGPSHIM: DF-2399 after openA: isopen=1 busy=1; after openB: isopen=1 busy=1
AGPSHIM: DF-2399 after closeA: isopen=0 busy=0 (B still has it OPEN; memory list now empty; state=0)
AGPSHIM: DF-2399 after closeB: isopen=0 busy=0
AGPSHIM: DF-2399 VERDICT: TWO opens produced ONE device_busy (count 1), and the FIRST close freed ALL AGP memory and returned busy to 0 while B still held the device open. Cross-process memory wipe + busy-count mismatch REPRODUCED.