fix(parity): hermetic live-remote master reads under pytest (Closes #610)

Remediate PR #788 review F1/F2: suite-wide hermetic mode prevents
git ls-remote from running in tests so feature worktrees no longer flip
legacy runtime-context assertions to live_stale, and unit tests stay offline.
Module flag survives patch.dict(clear=True); env override still wins.

Co-Authored-By: Grok 4.5 <[email protected]>

tests/test_master_parity_gate.py

@@ -212,13 +212,27 @@ class TestRemoteHeadCache(unittest.TestCase):
     """
 
     def setUp(self):
+        # These cases intentionally exercise the subprocess/cache path, so they
+        # opt out of suite-wide hermetic mode (PR #788 F1).
+        self._saved_hermetic = mp.hermetic_test_mode()
+        mp.set_hermetic_test_mode(False)
         mp._clear_remote_head_cache()
-        env = {k: v for k, v in os.environ.items()
-               if k != mp.ENV_TEST_LIVE_REMOTE_HEAD}
+        env = {
+            k: v for k, v in os.environ.items()
+            if k not in (mp.ENV_TEST_LIVE_REMOTE_HEAD,
+                         mp.ENV_TEST_ALLOW_LIVE_REMOTE_PROBE,
+                         "PYTEST_CURRENT_TEST")
+        }
+        # Allow the probe path under hermetic defenses while still mocking
+        # subprocess so no real network call runs.
+        env[mp.ENV_TEST_ALLOW_LIVE_REMOTE_PROBE] = "1"
         self._env = patch.dict(os.environ, env, clear=True)
         self._env.start()
         self.addCleanup(self._env.stop)
         self.addCleanup(mp._clear_remote_head_cache)
+        self.addCleanup(
+            lambda: mp.set_hermetic_test_mode(self._saved_hermetic)
+        )
 
     def _fake_run(self, sha):
         class _R:
@@ -256,6 +270,63 @@ class TestRemoteHeadCache(unittest.TestCase):
         self.assertEqual(calls["n"], 0)
 
 
+class TestHermeticLiveRemoteReads(unittest.TestCase):
+    """#610 / PR #788 F1/F2: suite hermetic mode never hits the network."""
+
+    def setUp(self):
+        self._saved = mp.hermetic_test_mode()
+        mp.set_hermetic_test_mode(True)
+        mp._clear_remote_head_cache()
+        self.addCleanup(lambda: mp.set_hermetic_test_mode(self._saved))
+        self.addCleanup(mp._clear_remote_head_cache)
+
+    def test_hermetic_mode_returns_none_without_subprocess(self):
+        run_calls = {"n": 0}
+
+        def boom(*args, **kwargs):
+            run_calls["n"] += 1
+            raise AssertionError("ls-remote must not run under hermetic mode")
+
+        env = {
+            k: v for k, v in os.environ.items()
+            if k not in (mp.ENV_TEST_LIVE_REMOTE_HEAD,
+                         mp.ENV_TEST_ALLOW_LIVE_REMOTE_PROBE)
+        }
+        with patch.dict(os.environ, env, clear=True):
+            with patch.object(mp.subprocess, "run", boom):
+                self.assertIsNone(
+                    mp.read_remote_master_head("/repo", remote="prgs")
+                )
+        self.assertEqual(run_calls["n"], 0)
+
+    def test_hermetic_mode_survives_clear_true_env(self):
+        """Module flag, not env pin: clear=True cannot re-enable the probe."""
+        run_calls = {"n": 0}
+
+        def boom(*args, **kwargs):
+            run_calls["n"] += 1
+            raise AssertionError("ls-remote must not run after clear=True")
+
+        with patch.dict(os.environ, {}, clear=True):
+            with patch.object(mp.subprocess, "run", boom):
+                self.assertIsNone(mp.read_remote_master_head("/repo"))
+        self.assertEqual(run_calls["n"], 0)
+
+    def test_explicit_override_still_wins_under_hermetic(self):
+        run_calls = {"n": 0}
+
+        def boom(*args, **kwargs):
+            run_calls["n"] += 1
+            raise AssertionError("override must bypass subprocess")
+
+        with patch.dict(os.environ, {mp.ENV_TEST_LIVE_REMOTE_HEAD: SHA_B}):
+            with patch.object(mp.subprocess, "run", boom):
+                self.assertEqual(
+                    mp.read_remote_master_head("/repo"), SHA_B
+                )
+        self.assertEqual(run_calls["n"], 0)
+
+
 class TestServerWiring(unittest.TestCase):
     """Integration with the gate choke point in the server namespace."""