The gateway auto-restart phase used to swallow every exception at debug
level, so tests driving cmd_update end-to-end never noticed it touching
real gateway discovery. With #78574 surfacing an aborted restart as a
failed update, an unmocked find_gateway_pids on a box with a live
gateway hits the conftest live-system guard and turns into a spurious
sys.exit(1).
Add an autouse fixture in test_cmd_update.py (discovery returns nothing,
systemd unsupported) and the same seams in test_update_head_moved_gate's
helper so the phase is a clean no-op for tests that do not assert on
gateway restarts.
A detached/pinned checkout can report 'N new commit(s)' against origin,
run the ff-only merge successfully, and still sit on the old commit
afterward (the branch-switch step re-detaches to the raw SHA). Before
this guard 'hermes update' printed '✓ Code updated!' and reinstalled
deps + rebuilt the desktop app against the stale tree - no error, no
warning, 'hermes doctor' healthy.
Compare pre-pull and post-pull HEAD; if they match, fail loudly with a
reattach hint instead of claiming success.
Teknium