The live lock-holder tests could hang or leak:
- the handshake readline had no deadline and stderr went to DEVNULL,
so a child stuck on import blocked the worker with no diagnostics;
- the holder slept 120s, outliving a killed pytest while holding
gateway.lock;
- `assert acquire_gateway_runtime_lock()` vanishes under -O;
- kill() hit only the Windows venv launcher, never the self-reported
interpreter, and pipes were never closed (ResourceWarning per test);
- the discovery test relied on list_profiles() resolving to the temp
HERMES_HOME and compared unresolved paths (/var vs /private/var on
macOS, 8.3 names on Windows).
The holder now blocks on stdin, reports failure via exit + captured
stderr, and teardown kills the launcher tree plus the reported PID and
reaps via communicate(). The four class tests share one class-scoped
holder with per-test restore of gateway.pid / gateway.lock (5 spawns ->
2), and discovery pins the profile roots like the named-pipe live test.
Also read gateway.pid with utf-8-sig (windows-footguns lane).
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