Per-card measurement was unreachable for every card but ordinal 0: the driver
set HIP_VISIBLE_DEVICES=N and still passed N as the device argument, so the
probe called hipSetDevice(N) on a runtime where the mask left only ordinal 0.
The bats stub reported the env var rather than the argument it received, so
the suite asserted the mask was set and never noticed the collision.
- one selector: the ordinal is passed as argv, the mask is never set
- a probe that fails is now exit 5 and names probe + device; the sweep still
measures the remaining cards instead of swallowing the failure
- the guard fails closed when `fuser` is missing (gpu_busy_percent reads 0 for
a resident-but-idle service), with PCIE_PROBE_FUSER as the test seam
- stub probes now model the HIP mask rule; the pre-existing per-device test
goes red against the old driver, which is the regression proof
Refs #60
Frank
71a7e5cb9a