diff --git a/test/conftest.py b/test/conftest.py
index 213dc5b..8e96e46 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -56,6 +56,25 @@ if sys.platform == "win32":
         from utils import misc as _misc
 
         _win_input.user32 = _NoRealInputUser32(_win_input.user32)
+        # Tests must not post to the real Discord either. Config reads the webhook
+        # from the repo's .env, and bot paths under test call
+        # _save_error_screenshot -> messenger.send_error: on 2026-09-15 a town-manager
+        # test sent a real "maintenance failed - Buy consumables failed (vendor not
+        # found)" alert while the live bot was fine.
+        from config import Config as _Config
+        from messages import discord_embeds as _discord_embeds, generic_api as _generic_api
+
+        _Config().general["custom_message_hook"] = ""
+        _Config().general["custom_loot_message_hook"] = ""
+        _Config().general["message_api_type"] = ""
+
+        class _NoWebhook:
+            @staticmethod
+            def from_url(*args, **kwargs):
+                raise RuntimeError("Discord disabled under pytest")
+
+        _discord_embeds.SyncWebhook = _NoWebhook
+        _generic_api.requests = type("_NoRequests", (), {"post": staticmethod(lambda *a, **k: None)})()
         # Window moves / focus steals: tests must not reposition or front D2R either.
         for _name in ("SetWindowPos", "SetForegroundWindow", "ShowWindow"):
             setattr(_misc, _name, lambda *args, **kwargs: None)
diff --git a/test/test_no_real_side_effects.py b/test/test_no_real_side_effects.py
new file mode 100644
index 0000000..c13a525
--- /dev/null
+++ b/test/test_no_real_side_effects.py
@@ -0,0 +1,21 @@
+"""The suite must not reach the real desktop or the real Discord (see conftest.py)."""
+import pytest
+
+
+def test_messenger_is_disabled_under_pytest():
+    from messages import Messenger
+
+    assert not Messenger().enabled, "tests would post to the real Discord webhook from .env"
+
+
+def test_discord_webhook_cannot_be_created_under_pytest():
+    from messages import discord_embeds
+
+    with pytest.raises(RuntimeError):
+        discord_embeds.SyncWebhook.from_url("https://discord.com/api/webhooks/1/x")
+
+
+def test_real_input_is_blocked_under_pytest():
+    from input_layer import win_input
+
+    assert type(win_input.user32).__name__ == "_NoRealInputUser32"