CI test shard has no PyPI egress: the real 'pip install packaging==20.9'
in test_core_package_is_not_shadowed failed (the pypi.org reachability
probe passed but the actual install didn't), failing slice 2/6.
- Prove the anti-shadow invariant deterministically: synthesize a fake
'packaging' in the durable target with a sentinel and assert the import
still resolves to the core copy (TestCoreNeverShadowed). No network.
- Cover the install wire offline: stub subprocess and assert --target +
--constraint are built in durable mode and absent in venv-scoped mode
(TestInstallArgConstruction).
- Gate the genuine PyPI install behind HERMES_RUN_NETWORK_TESTS=1 (opt-in,
skipped in CI) instead of a flaky reachability probe that doesn't predict
install success.
41b9b7e719