fix: test suite sent real push notifications via the developer's .env

tests/conftest.py

@@ -0,0 +1,39 @@
+"""Shared test fixtures.
+
+The autouse fixture here exists because of a real incident (2026-08-18): the
+`sync` CLI tests invoke the actual command, which calls `load_config()`, which
+calls `load_dotenv()` — so the developer's real `.env` was loaded and its
+`NTFY_TOPIC` used. Every `pytest` run fired real push notifications at the
+developer's phone, including a fabricated "3 conversations failed to export"
+from a fixture. Nothing appeared in the log to explain it, because the tests
+pass `--no-log-file`.
+
+The lesson generalises past ntfy: any test that exercises a command end to end
+inherits whatever is in `.env` unless the environment is neutralised first.
+"""
+
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def _no_outbound_side_effects(monkeypatch):
+    """Neutralise every environment variable that could reach a real service.
+
+    Set to empty/unroutable values rather than deleted: `load_dotenv` is called
+    with ``override=False``, which only skips keys **already present** in the
+    environment. Deleting a key would let the developer's `.env` put it back.
+
+    Individual tests may still `monkeypatch.setenv` these — that is how the
+    notification tests point at a dead local port on purpose.
+    """
+    # Notifications: an empty topic disables sending outright (`is_configured`
+    # strips and checks truthiness), and the server is pointed at a closed port
+    # so even a test that sets its own topic cannot reach the internet.
+    monkeypatch.setenv("NTFY_TOPIC", "")
+    monkeypatch.setenv("NTFY_SERVER", "http://127.0.0.1:9")
+    monkeypatch.setenv("NTFY_TOKEN", "")
+
+    # Joplin: a test that reached the developer's running desktop instance would
+    # create or overwrite real notes in their archive.
+    monkeypatch.setenv("JOPLIN_API_URL", "http://127.0.0.1:9")
+    monkeypatch.setenv("JOPLIN_API_TOKEN", "")