diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..4e51679
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2025-09-12 - Prevent Error Details Leakage in Auth Decorators
+**Vulnerability:** Exception details (`str(e)`) were returned in HTTP 401 responses inside the `login_required` decorator, leaking internal error messages and system internals to unauthenticated users.
+**Learning:** Returning exception text in authentication failure handlers risks exposing sensitive database or internal application state to attackers.
+**Prevention:** Always fail securely by returning generic error messages (e.g. `{"error": "Unauthorized"}`) on authentication failures.
diff --git a/auth/utils.py b/auth/utils.py
index 4bded89..a060433 100644
--- a/auth/utils.py
+++ b/auth/utils.py
@@ -128,8 +128,8 @@ def decorated_function(*args, **kwargs):
             g.user_id = user_id
             g.user = user_data
             return f(*args, **kwargs)
-        except Exception as e:
-            return jsonify({'error': 'Unauthorized', 'details': str(e)}), 401
+        except Exception:
+            return jsonify({'error': 'Unauthorized'}), 401
     return decorated_function
 
 
diff --git a/src/handoff/__init__.py b/src/handoff/__init__.py
new file mode 100644
index 0000000..0f55842
--- /dev/null
+++ b/src/handoff/__init__.py
@@ -0,0 +1 @@
+"""Handoff module package."""
diff --git a/tests/test_auth.py b/tests/test_auth.py
new file mode 100644
index 0000000..05d79ae
--- /dev/null
+++ b/tests/test_auth.py
@@ -0,0 +1,33 @@
+import sys
+from unittest.mock import MagicMock
+
+# Mock external cache_db dependency before importing auth.utils
+mock_cache_db = MagicMock()
+sys.modules['cache_db'] = mock_cache_db
+sys.modules['cache_db.redis_client'] = mock_cache_db.redis_client
+sys.modules['cache_db.models'] = mock_cache_db.models
+
+from flask import Flask, jsonify
+from auth.utils import login_required
+
+def test_login_required_unauthorized_does_not_leak_details(monkeypatch):
+    app = Flask(__name__)
+
+    @app.route("/protected")
+    @login_required
+    def protected_route():
+        return jsonify({"message": "success"})
+
+    # Force verify_jwt_in_request to raise an Exception with sensitive details
+    def mock_verify():
+        raise RuntimeError("Sensitive internal database stack trace or token parsing error")
+
+    monkeypatch.setattr("auth.utils.verify_jwt_in_request", mock_verify)
+
+    with app.test_client() as client:
+        response = client.get("/protected")
+        assert response.status_code == 401
+        data = response.get_json()
+        assert data == {"error": "Unauthorized"}
+        assert "details" not in data
+        assert "Sensitive internal" not in str(data)