diff --git a/tests/gateway/test_update_command.py b/tests/gateway/test_update_command.py
index fa223a42f..5cc7f206e 100644
--- a/tests/gateway/test_update_command.py
+++ b/tests/gateway/test_update_command.py
@@ -51,10 +51,16 @@ class TestHandleUpdateCommand:
         event = _make_event()
         monkeypatch.setenv("HERMES_MANAGED", "homebrew")
 
-        result = await runner._handle_update_command(event)
+        # Guard: prevent any accidental fall-through from spawning a real
+        # `hermes update --gateway` against the CI checkout. The managed-install
+        # guard should return before Popen is ever reached, but mock it as
+        # belt-and-suspenders so a premature return doesn't corrupt the repo.
+        with patch("subprocess.Popen") as mock_popen:
+            result = await runner._handle_update_command(event)
 
         assert "managed by Homebrew" in result
         assert "brew upgrade hermes-agent" in result
+        mock_popen.assert_not_called()  # must return before reaching Popen
 
     @pytest.mark.asyncio
     async def test_no_git_directory(self, tmp_path):
@@ -388,16 +394,16 @@ class TestUpdateCommandPlatformGate:
         blocked by the allowlist gate before any side effects fire."""
         runner = _make_runner()
         event = _make_event(platform=Platform.WEBHOOK)
-        # Stop _handle_update_command from progressing further if the gate
-        # somehow lets the event through — the assertion on the returned
-        # string is the real test.
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        # Guard: platform gate must fire before any real subprocess spawn.
+        with patch("subprocess.Popen") as mock_popen:
+            result = await runner._handle_update_command(event)
 
         # The exact rejection message comes from
         # ``gateway.update.platform_not_messaging`` translation key.
         assert "only available from messaging platforms" in result
+        mock_popen.assert_not_called()
 
     @pytest.mark.asyncio
     async def test_blocks_api_server_platform(self, monkeypatch):
@@ -408,9 +414,11 @@ class TestUpdateCommandPlatformGate:
         event = _make_event(platform=Platform.API_SERVER)
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        with patch("subprocess.Popen") as mock_popen:
+            result = await runner._handle_update_command(event)
 
         assert "only available from messaging platforms" in result
+        mock_popen.assert_not_called()
 
     @pytest.mark.asyncio
     async def test_allows_plugin_platform_via_registry_fallback(self, monkeypatch):
@@ -439,7 +447,8 @@ class TestUpdateCommandPlatformGate:
         event = _make_event(platform=Platform.DISCORD)
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        with patch("subprocess.Popen"):
+            result = await runner._handle_update_command(event)
 
         # The gate must NOT have rejected us — anything other than the
         # ``platform_not_messaging`` rejection string is acceptable here.
@@ -467,7 +476,8 @@ class TestUpdateCommandPlatformGate:
         event = _make_event(platform=Platform.MATTERMOST)
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        with patch("subprocess.Popen"):
+            result = await runner._handle_update_command(event)
 
         assert "only available from messaging platforms" not in result
 
@@ -492,7 +502,8 @@ class TestUpdateCommandPlatformGate:
         event = _make_event(platform=Platform.HOMEASSISTANT)
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        with patch("subprocess.Popen"):
+            result = await runner._handle_update_command(event)
 
         assert "only available from messaging platforms" not in result
 
@@ -509,7 +520,8 @@ class TestUpdateCommandPlatformGate:
         event = _make_event(platform=Platform.TELEGRAM)
         monkeypatch.setenv("HERMES_MANAGED", "")
 
-        result = await runner._handle_update_command(event)
+        with patch("subprocess.Popen"):
+            result = await runner._handle_update_command(event)
 
         assert "only available from messaging platforms" not in result