diff --git a/CHANGELOG.md b/CHANGELOG.md
index a04f85c..0ac3880 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,13 @@
 All notable changes to this project will be documented here.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+
+### Fixed
+- **The test suite sent real push notifications to the developer's phone.** `TestSyncCommand` invokes the actual `sync` command, which calls `load_config()`, which calls `load_dotenv()` — so the real `.env` was loaded and its live `NTFY_TOPIC` used for the POST. Every `pytest` run fired three or four pushes, including a fabricated "codex: 3 conversation(s) failed to export" straight out of a fixture, which is worse than noise: it reports a failure that never happened. Nothing appeared in `cache/logs/exporter.log` to explain it, because every test invocation passes `--no-log-file`.
+
+  A `tests/conftest.py` autouse fixture now neutralises the environment for every test: `NTFY_TOPIC`/`NTFY_TOKEN` are emptied, and `NTFY_SERVER` and `JOPLIN_API_URL` are pointed at a closed local port, so a stray topic cannot reach the internet and a test cannot write notes into a real Joplin instance. The values are **emptied rather than deleted** — `load_dotenv(override=False)` skips only keys already present, so deleting one lets `.env` put it back. Verified by instrumenting `requests` across a full run: zero outbound requests, where the same instrumentation without the fixture records POSTs to the live ntfy topic.
+
 ## [0.9.0] - 2026-08-18
 
 ### Fixed
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..e5d6ff9
--- /dev/null
+++ b/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", "")
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 020a491..6af4c1d 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -624,3 +624,40 @@ class TestNotifySend:
         monkeypatch.setenv("NTFY_TOPIC", "unit-test-topic")
         monkeypatch.setenv("NTFY_NOTIFY", "off")
         assert notify_mod.is_configured() is False
+
+
+class TestNoRealNotificationsDuringTests:
+    """Regression guard for the 2026-08-18 incident: the suite pushed to the
+    developer's real ntfy topic because `sync` loads `.env` via `load_dotenv`.
+
+    Asserts the conftest neutralisation holds even though a real `.env` with a
+    live NTFY_TOPIC sits beside the tests.
+    """
+
+    def test_notifications_are_disabled(self):
+        from src import notify as notify_mod
+
+        assert notify_mod.is_configured() is False
+
+    def test_dotenv_cannot_reintroduce_a_topic(self):
+        """`load_dotenv(override=False)` skips keys already present — including
+        empty ones. Deleting the var instead of emptying it would reopen this."""
+        import os
+
+        from dotenv import load_dotenv
+
+        from src import notify as notify_mod
+
+        load_dotenv(override=False)
+        assert os.getenv("NTFY_TOPIC", "").strip() == ""
+        assert notify_mod.is_configured() is False
+
+    def test_send_cannot_reach_the_public_server(self, monkeypatch):
+        """Even a test that sets its own topic is pinned to a dead local port."""
+        import os
+
+        from src import notify as notify_mod
+
+        monkeypatch.setenv("NTFY_TOPIC", "some-topic")
+        assert "127.0.0.1" in os.getenv("NTFY_SERVER", "")
+        assert notify_mod.send("t", "m") is False