UI smoke tests
~~~~~~~~~~~~~~

These tests launch each GUI (axis, touchy, gmoccapy, qtdragon) under
xvfb-run against an existing sim config and verify the GUI starts and
the NML task is reachable. Phase 1 ("does it start"); functional
checks (load G-code, jog, MDI) belong in tests/ui-functional/.

Each test directory contains:
  test.sh       launches the GUI under xvfb-run, runs drive.py
  checkresult   examines the captured output for crash markers
  skip          skips this test only when xvfb-run is not on the host

Shared helpers live in _lib/:
  drive.py            common NML driver, prints UI_SMOKE_OK on success
  launch.sh           xvfb-run wrapper, signal escalation for shutdown
  cleanup-runtime.sh  belt-and-suspenders: kill stray daemons, ipcrm
                      shared memory, drop /tmp/linuxcnc.lock
  checkresult.sh      shared pass/fail predicate
  skip-if-missing.sh  shared skip predicate

Skip vs fail policy: the only condition we skip on is xvfb-run absence
(rare local dev env). Python and gi typelib deps the GUIs need are
declared in debian/control under !nocheck so apt-get build-dep
installs them on CI; if they are missing the test should fail loudly
rather than silently skip, so missing deps surface during review.