diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b612c26e..09c55d10e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Pin `Path.home()` under unit tests via a session-scoped autouse conftest fixture, fixing 56 Windows runner failures on the new `windows-2025-vs2026` GitHub-hosted image where `USERPROFILE`/`HOMEDRIVE`+`HOMEPATH` are not seeded for pytest workers; also patch the `_check_and_notify_updates` import binding in the disabled-self-update test so it no longer races on the version-check cache. (#1270)
+
 ## [0.13.0] - 2026-05-11
 
 ### Breaking Changes
diff --git a/tests/unit/conftest.py b/tests/unit/conftest.py
new file mode 100644
index 000000000..ba9a55ef6
--- /dev/null
+++ b/tests/unit/conftest.py
@@ -0,0 +1,63 @@
+"""Unit-test conftest: hermetic HOME isolation.
+
+The session-scoped autouse fixture below pins ``Path.home()`` to a tmp
+directory for the entire unit-test session. Two reasons:
+
+1. Hermeticity. Unit tests must not read or write the contributor's real
+   ``~`` (config files, runtimes, caches). Tests that call
+   ``RuntimeManager()`` or ``Path.home()`` directly previously inherited
+   whatever HOME the runner had.
+2. Windows runner robustness. On the ``windows-2025-vs2026`` GitHub
+   Actions image the ``USERPROFILE`` / ``HOMEDRIVE`` + ``HOMEPATH``
+   triplet is not set under the pytest worker subprocess, so
+   ``Path.home()`` raises ``RuntimeError: Could not determine home
+   directory.`` This fixture sets the platform-correct trio so
+   ``Path.home()`` always resolves to ``<tmp>`` regardless of runner
+   image.
+
+Per-test fixtures that need a different HOME (e.g. tests/unit/integration
+that exercise scope resolution) keep using ``monkeypatch.setenv`` and
+override this baseline; the function-scoped monkeypatch wins over the
+session-scoped baseline for the duration of the test.
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import pytest
+
+
+def _set_home_env(home: Path) -> None:
+    """Set ``HOME`` and the Windows-equivalent vars to ``home``.
+
+    ``Path.home()`` consults ``HOME`` on POSIX but ``USERPROFILE``
+    (with ``HOMEDRIVE`` + ``HOMEPATH`` fallback) on Windows.
+    """
+    home_str = str(home)
+    os.environ["HOME"] = home_str
+    if os.name == "nt":
+        os.environ["USERPROFILE"] = home_str
+        drive, _, tail = home_str.partition(":")
+        if tail:
+            os.environ["HOMEDRIVE"] = f"{drive}:"
+            os.environ["HOMEPATH"] = tail
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _hermetic_home(tmp_path_factory: pytest.TempPathFactory) -> None:
+    """Pin ``Path.home()`` to a per-session tmp dir for all unit tests."""
+    home = tmp_path_factory.mktemp("apm-unit-home")
+    previous = {
+        key: os.environ.get(key) for key in ("HOME", "USERPROFILE", "HOMEDRIVE", "HOMEPATH")
+    }
+    _set_home_env(home)
+    try:
+        yield
+    finally:
+        for key, value in previous.items():
+            if value is None:
+                os.environ.pop(key, None)
+            else:
+                os.environ[key] = value
diff --git a/tests/unit/test_update_command.py b/tests/unit/test_update_command.py
index 275dbf178..2236d2af5 100644
--- a/tests/unit/test_update_command.py
+++ b/tests/unit/test_update_command.py
@@ -40,6 +40,7 @@ def test_manual_update_command_uses_windows_installer(self):
         self.assertIn("powershell", command.lower())
 
     @patch("apm_cli.commands.self_update.is_self_update_enabled", return_value=False)
+    @patch("apm_cli.commands._helpers.is_self_update_enabled", return_value=False)
     @patch(
         "apm_cli.commands.self_update.get_self_update_disabled_message",
         return_value="Update with: pixi update apm-cli",
@@ -51,6 +52,7 @@ def test_update_command_respects_disabled_policy(
         mock_get,
         mock_run,
         mock_message,
+        mock_enabled_helpers,
         mock_enabled,
     ):
         """Disabled self-update policy should print guidance and skip installer."""