diff --git a/tests/test_create_issue.py b/tests/test_create_issue.py
index cdfdb0c..b2fdb68 100644
--- a/tests/test_create_issue.py
+++ b/tests/test_create_issue.py
@@ -11,6 +11,7 @@ import json
 import sys
 import tempfile
 import unittest
+import contextlib
 from unittest.mock import MagicMock, patch
 
 # The module under test lives in the repo root, not a package.
@@ -38,7 +39,8 @@ class TestArgParsing(unittest.TestCase):
     @patch("create_issue.api_request", return_value={"number": 1, "html_url": "http://x/1"})
     @patch("create_issue.get_credentials", return_value=FAKE_CREDS)
     def test_minimal_args(self, _cred, _api):
-        rc = create_issue.main(["--title", "Hello"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = create_issue.main(["--title", "Hello"])
         self.assertEqual(rc, 0)
 
     def test_missing_title_exits(self):
@@ -50,7 +52,8 @@ class TestArgParsing(unittest.TestCase):
     @patch("create_issue.get_credentials", return_value=FAKE_CREDS)
     def test_remote_choices(self, _cred, _api):
         for remote in ("dadeschools", "prgs"):
-            rc = create_issue.main(["--remote", remote, "--title", "X"])
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                rc = create_issue.main(["--remote", remote, "--title", "X"])
             self.assertEqual(rc, 0, f"--remote {remote} should be accepted")
 
     def test_invalid_remote_exits(self):
@@ -138,7 +141,8 @@ class TestAuthFailure(unittest.TestCase):
 
     @patch("create_issue.get_credentials", return_value=("", ""))
     def test_no_credentials_returns_1(self, _cred):
-        rc = create_issue.main(["--title", "T"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = create_issue.main(["--title", "T"])
         self.assertEqual(rc, 1)
 
 
@@ -152,7 +156,8 @@ class TestAPIError(unittest.TestCase):
     def test_api_error_returns_1(self, _cred):
         with patch("create_issue.api_request",
                    side_effect=RuntimeError("HTTP 422: duplicate")):
-            rc = create_issue.main(["--title", "Dup"])
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                rc = create_issue.main(["--title", "Dup"])
             self.assertEqual(rc, 1)
 
 
diff --git a/tests/test_create_pr.py b/tests/test_create_pr.py
index 7b9c31b..b55dafb 100644
--- a/tests/test_create_pr.py
+++ b/tests/test_create_pr.py
@@ -7,6 +7,7 @@ import io
 import json
 import sys
 import unittest
+import contextlib
 from unittest.mock import MagicMock, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -34,7 +35,8 @@ class TestArgParsing(unittest.TestCase):
     @patch("create_pr.urllib.request.urlopen", return_value=_mock_urlopen())
     @patch("create_pr.get_credentials", return_value=FAKE_CREDS)
     def test_minimal_required_args(self, _cred, _url):
-        rc = create_pr.main(["--title", "PR Title", "--head", "feat/branch"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = create_pr.main(["--title", "PR Title", "--head", "feat/branch"])
         self.assertEqual(rc, 0)
 
     def test_missing_title_exits(self):
diff --git a/tests/test_manage_labels.py b/tests/test_manage_labels.py
index 71fee7c..cdccf76 100644
--- a/tests/test_manage_labels.py
+++ b/tests/test_manage_labels.py
@@ -2,9 +2,11 @@
 
 All API calls are mocked — no real network or keychain access.
 """
+import io
 import json
 import sys
 import unittest
+import contextlib
 from unittest.mock import MagicMock, call, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -33,7 +35,8 @@ class TestLabelCreation(unittest.TestCase):
 
         # Patch sys.argv to avoid --dry
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         # The GET call happens, but no POST calls for label creation
         get_calls = [c for c in mock_api.call_args_list if c[0][0] == "GET"]
@@ -59,7 +62,8 @@ class TestLabelCreation(unittest.TestCase):
 
         mock_api.side_effect = side_effect
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         post_calls = [
             c for c in mock_api.call_args_list
@@ -79,7 +83,8 @@ class TestDryRun(unittest.TestCase):
         mock_api.return_value = []  # no existing labels
 
         with patch.object(sys, "argv", ["manage_labels.py", "--dry"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         # Only the GET call should be made, no POST or PUT
         for c in mock_api.call_args_list:
@@ -107,7 +112,8 @@ class TestLabelMapping(unittest.TestCase):
 
         mock_api.side_effect = side_effect
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         put_calls = [c for c in mock_api.call_args_list if c[0][0] == "PUT"]
         self.assertEqual(len(put_calls), len(manage_labels.MAPPING))
diff --git a/tests/test_merge_pr.py b/tests/test_merge_pr.py
index 4dca610..9647b72 100644
--- a/tests/test_merge_pr.py
+++ b/tests/test_merge_pr.py
@@ -45,13 +45,17 @@ class TestMergeDisabled(unittest.TestCase):
         mock_api.assert_not_called()
 
     def test_message_points_to_gated_workflow(self):
+        from _pytest.monkeypatch import MonkeyPatch
         import io
-        import contextlib
         with patch("merge_pr.get_auth_header", return_value=FAKE_CREDS), \
                 patch("merge_pr.api_request") as mock_api:
             buf = io.StringIO()
-            with contextlib.redirect_stderr(buf):
+            monkeypatch = MonkeyPatch()
+            monkeypatch.setattr(sys, "stderr", buf)
+            try:
                 rc = merge_pr.main(["--pr-number", "81"])
+            finally:
+                monkeypatch.undo()
         self.assertEqual(rc, 2)
         mock_api.assert_not_called()
         msg = buf.getvalue().lower()
diff --git a/tests/test_migrate_profiles.py b/tests/test_migrate_profiles.py
index 84bcaa9..abbe5df 100644
--- a/tests/test_migrate_profiles.py
+++ b/tests/test_migrate_profiles.py
@@ -9,6 +9,8 @@ import shutil
 from unittest.mock import patch
 from io import StringIO
 
+from _pytest.monkeypatch import MonkeyPatch
+
 # Add project root to sys.path
 PROJECT_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 if PROJECT_ROOT not in sys.path:
@@ -127,24 +129,29 @@ class TestMigrateProfiles(unittest.TestCase):
         v2_data = migrate_profiles.migrate_v1_to_v2(self.v1_content)
         self.assertTrue(migrate_profiles.validate_v2_data(v2_data))
 
-    @patch("sys.stdout", new_callable=StringIO)
-    def test_dry_run_default(self, mock_stdout):
+    def test_dry_run_default(self):
         """Verify that running without -w prints generated config without modifying files."""
-        output_file = os.path.join(self.temp_dir, "migrated_dry.json")
-        test_args = [
-            "migrate_profiles.py",
-            "-i", self.input_file,
-            "-o", output_file
-        ]
-        with patch.object(sys, "argv", test_args):
-            with self.assertRaises(SystemExit) as cm:
-                migrate_profiles.main()
-            self.assertEqual(cm.exception.code, 0)
+        monkeypatch = MonkeyPatch()
+        mock_stdout = StringIO()
+        monkeypatch.setattr(sys, "stdout", mock_stdout)
+        try:
+            output_file = os.path.join(self.temp_dir, "migrated_dry.json")
+            test_args = [
+                "migrate_profiles.py",
+                "-i", self.input_file,
+                "-o", output_file
+            ]
+            with patch.object(sys, "argv", test_args):
+                with self.assertRaises(SystemExit) as cm:
+                    migrate_profiles.main()
+                self.assertEqual(cm.exception.code, 0)
 
-        self.assertFalse(os.path.exists(output_file))
-        self.assertFalse(os.path.exists(f"{self.input_file}.bak"))
+            self.assertFalse(os.path.exists(output_file))
+            self.assertFalse(os.path.exists(f"{self.input_file}.bak"))
 
-        stdout_output = mock_stdout.getvalue()
+            stdout_output = mock_stdout.getvalue()
+        finally:
+            monkeypatch.undo()
         self.assertIn("DRY-RUN MODE", stdout_output)
         self.assertIn("version", stdout_output)
         self.assertIn("identities", stdout_output)
@@ -165,13 +172,18 @@ class TestMigrateProfiles(unittest.TestCase):
             json.dump(sensitive, f)
 
         test_args = ["migrate_profiles.py", "-i", self.input_file]
-        with patch("sys.stdout", new_callable=StringIO) as mock_stdout:
+        monkeypatch = MonkeyPatch()
+        mock_stdout = StringIO()
+        monkeypatch.setattr(sys, "stdout", mock_stdout)
+        try:
             with patch.object(sys, "argv", test_args):
                 with self.assertRaises(SystemExit) as cm:
                     migrate_profiles.main()
                 self.assertEqual(cm.exception.code, 0)
 
-        stdout_output = mock_stdout.getvalue()
+            stdout_output = mock_stdout.getvalue()
+        finally:
+            monkeypatch.undo()
         self.assertNotIn("super-secret-token-value", stdout_output)
         self.assertNotIn("token", stdout_output.lower())
 
diff --git a/tests/test_prs.py b/tests/test_prs.py
index 0255584..b86a233 100644
--- a/tests/test_prs.py
+++ b/tests/test_prs.py
@@ -4,6 +4,8 @@ Mocks api_request and credentials.
 """
 import sys
 import unittest
+import io
+import contextlib
 from unittest.mock import patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -24,14 +26,16 @@ class TestListPRs(unittest.TestCase):
         mock_api.return_value = [
             {"number": 1, "title": "PR 1", "head": {"ref": "branch1"}, "base": {"ref": "main"}, "html_url": "http://url1", "mergeable": True}
         ]
-        rc = list_prs.main([])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = list_prs.main([])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()
 
     @patch("list_prs.api_request", return_value=[])
     @patch("list_prs.get_auth_header", return_value=FAKE_CREDS)
     def test_list_prs_empty(self, _auth, mock_api):
-        rc = list_prs.main(["--state", "closed"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = list_prs.main(["--state", "closed"])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()
 
diff --git a/tests/test_python_cli.py b/tests/test_python_cli.py
index 2ea8f03..55d727a 100644
--- a/tests/test_python_cli.py
+++ b/tests/test_python_cli.py
@@ -4,6 +4,8 @@ All tests mock credentials and API requests so no real network calls are made.
 """
 import sys
 import unittest
+import io
+import contextlib
 from unittest.mock import patch, MagicMock
 
 # The modules under test live in the repo root
@@ -31,7 +33,8 @@ class TestCloseIssueCLI(unittest.TestCase):
     @patch("close_issue.api_request")
     @patch("close_issue.get_auth_header", return_value=FAKE_AUTH)
     def test_successful_close(self, _auth, mock_api):
-        rc = close_issue.main(["42"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = close_issue.main(["42"])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()
         url = mock_api.call_args[0][1]
@@ -69,7 +72,8 @@ class TestMarkIssueCLI(unittest.TestCase):
             [{"id": 101, "name": "status:in-progress"}],
             [{"name": "status:in-progress"}],
         ]
-        rc = mark_issue.main(["15", "start"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = mark_issue.main(["15", "start"])
         self.assertEqual(rc, 0)
         self.assertEqual(mock_api.call_count, 2)
         
diff --git a/tests/test_review_pr.py b/tests/test_review_pr.py
index 119bb95..d28ff01 100644
--- a/tests/test_review_pr.py
+++ b/tests/test_review_pr.py
@@ -79,15 +79,19 @@ class TestAPIPayload(unittest.TestCase):
         self.assertEqual(mock_api.call_count, 0)
 
     def test_merge_flag_message_points_to_gated_workflow(self):
+        from _pytest.monkeypatch import MonkeyPatch
         import io
-        import contextlib
         with patch("review_pr.get_auth_header", return_value=FAKE_CREDS), \
                 patch("review_pr.api_request") as mock_api:
             buf = io.StringIO()
-            with contextlib.redirect_stderr(buf):
+            monkeypatch = MonkeyPatch()
+            monkeypatch.setattr(sys, "stderr", buf)
+            try:
                 rc = review_pr.main([
                     "--pr-number", "81", "--event", "APPROVE", "--merge",
                 ])
+            finally:
+                monkeypatch.undo()
         self.assertEqual(rc, 2)
         self.assertEqual(mock_api.call_count, 0)
         msg = buf.getvalue().lower()
diff --git a/tests/test_review_proofs.py b/tests/test_review_proofs.py
index d67bfe6..d981eb3 100644
--- a/tests/test_review_proofs.py
+++ b/tests/test_review_proofs.py
@@ -14,6 +14,7 @@ each precondition of a blind queue review:
 
 These are the harness assertions from the issue's Required behavior 7.
 """
+import io
 import sys
 import unittest
 
@@ -463,5 +464,30 @@ class TestFinalReport(unittest.TestCase):
         self.assertFalse(report["merge_allowed"])
 
 
+class TestStdoutIsolation(unittest.TestCase):
+    """Regression test for #178: tests must not close or corrupt stdout/stderr
+    (prevents need for junitxml workaround in full suite runs and review validation).
+    """
+
+    def test_stdout_remains_usable(self):
+        """After typical test activity (mocks, redirects, prints from mains), stdout should be usable."""
+        # Verify not closed
+        self.assertFalse(getattr(sys.stdout, "closed", False))
+        # Should be able to write (even if captured by pytest)
+        try:
+            sys.stdout.write("")
+            sys.stdout.flush()
+        except Exception as exc:
+            self.fail(f"stdout write failed after test activity: {exc}")
+
+    def test_stderr_remains_usable(self):
+        self.assertFalse(getattr(sys.stderr, "closed", False))
+        try:
+            sys.stderr.write("")
+            sys.stderr.flush()
+        except Exception as exc:
+            self.fail(f"stderr write failed: {exc}")
+
+
 if __name__ == "__main__":
     unittest.main()