== DF-2399 fixed kernel (ACHARNESS #7) ==
AGPSHIM: DF-2399 after openA: isopen=2 busy=1; after openB: isopen=2 busy=1
AGPSHIM: DF-2399 after closeA: isopen=1 busy=1 (B still has it OPEN; memory list now NOT empty; state=1)
AGPSHIM: DF-2399 after closeB: isopen=0 busy=0
AGPSHIM: DF-2399 VERDICT: accounting behaved like a refcount (busyA0=1 busyA1=1 busyB=1) - not reproduced
(fix validated: refcounted isopen; cleanup exactly once at last close)