fix(secops): avoid stdout logging in investigations

server/secops/secops_mcp/tools/investigation_management.py

@@ -76,19 +76,21 @@ async def list_investigations(
     """
     try:
         chronicle = get_chronicle_client(project_id, customer_id, region)
-        print(f"Listing investigations (page_size={page_size})...")
+        logger.info("Listing investigations (page_size=%s)...", page_size)
 
         result = chronicle.list_investigations(
             page_size=page_size, page_token=page_token
         )
 
         investigations = result.get("investigations", [])
-        print(f"Successfully retrieved {len(investigations)} investigation(s)")
+        logger.info(
+            "Successfully retrieved %s investigation(s)", len(investigations)
+        )
         return result
 
     except Exception as e:
         error_msg = f"Error listing investigations: {str(e)}"
-        print(error_msg)
+        logger.exception(error_msg)
         return {"error": error_msg}
 
 

server/secops/tests/test_investigation_management_unit.py

@@ -0,0 +1,37 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Unit tests for investigation management tools."""
+
+import pytest
+
+from secops_mcp.tools.investigation_management import list_investigations
+
+
+@pytest.mark.asyncio
+async def test_list_investigations_does_not_write_stdout(
+    monkeypatch, capsys
+) -> None:
+    """Ensure list diagnostics cannot corrupt the MCP stdio transport."""
+
+    class ChronicleStub:
+        def list_investigations(self, **kwargs):
+            return {"investigations": []}
+
+    monkeypatch.setattr(
+        "secops_mcp.tools.investigation_management.get_chronicle_client",
+        lambda *args: ChronicleStub(),
+    )
+
+    assert await list_investigations(page_size=1) == {"investigations": []}
+    assert capsys.readouterr().out == ""