BUILD_EXIT=0
DF-0904 hammer2_update_spans loop-structure harness
media topology under spmp->iroot:
  [0] type=0x02 PFS@00
  [1] type=0x02 PFS@01
  [2] type=0x01 INDIRECT@02
  [3] type=0x02 PFS@03

buggy loop (iocom.c:313-341 verbatim, with watchdog):
  RESULT: INFINITE LOOP — watchdog tripped at 100001 iters (cursor stuck on the non-inode chain)

fixed loop (mirrors vfsops.c:1553-1566 sibling):
  RESULT: terminated, processed 3 PFS labels in 4 iters

verdict: BUGGY loop spins forever on a non-inode chain; FIXED loop terminates normally => bug confirmed at code level.
RUN_EXIT=0