diff --git a/alloc/lib/cache.py b/alloc/lib/cache.py
index 27a00e6..df61801 100644
--- a/alloc/lib/cache.py
+++ b/alloc/lib/cache.py
@@ -131,15 +131,17 @@ def cached(cache_type: str) -> Callable:
     """
 
     def decorator(func: Callable) -> Callable:
-        cache = DiskCache(
-            cache_dir=get_settings().cache_dir,
-            enabled=get_settings().cache_enabled,
-        )
-
         @functools.wraps(func)
         def wrapper(*args: Any, **kwargs: Any) -> Any:
+            # Resolve settings per call so that changes to the singleton
+            # (e.g. cache_enabled toggled in tests) are respected.
+            settings = get_settings()
+            cache = DiskCache(
+                cache_dir=settings.cache_dir,
+                enabled=settings.cache_enabled,
+            )
             key = cache._make_key(func.__name__, args, tuple(sorted(kwargs.items())))
-            ttl = get_settings().get_cache_ttl(cache_type)
+            ttl = settings.get_cache_ttl(cache_type)
 
             # Try cache first
             cached_value = cache.get(key, ttl)
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..09f1947
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,45 @@
+"""Shared pytest fixtures for the alloc test suite.
+
+The disk cache is disabled for the entire suite so that tests are hermetic
+and do not read stale entries from a shared ``./cache`` directory.  The cache
+key incorporates the identity of injected mock clients, which is unstable
+across garbage collection, so an enabled cache would cause cross-test
+pollution (a test reading a price cached by an unrelated test).
+
+Tests that specifically exercise caching behaviour (``test_cache.py`` and
+``test_cache_settings_integration.py``) patch ``get_settings`` with their own
+fake and are unaffected by this fixture.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+import alloc.config.settings as _settings_mod
+import alloc.lib.cache as _cache_mod
+
+# Capture the real get_settings once at import time so it can be restored
+# even after tests that reload alloc.lib.cache rebind its reference to a fake.
+_real_get_settings = _settings_mod.get_settings
+
+
+@pytest.fixture(autouse=True)
+def _isolate_disk_cache():
+    """Disable the disk cache and pin ``cache.get_settings`` to the real one.
+
+    Some tests reload ``alloc.lib.cache`` inside a ``patch`` block, which
+    rebinds ``cache.get_settings`` to a fake and leaks it into later tests.
+    This fixture forces the real reference back before every test and disables
+    caching on the settings singleton for the duration of the test, so the
+    decorated data-pipeline functions never touch the shared cache directory.
+    """
+    # Pin the cache module's get_settings to the real function (undo any leak).
+    _cache_mod.get_settings = _real_get_settings
+
+    settings = _real_get_settings()
+    original_enabled = settings.cache_enabled
+    settings.cache_enabled = False
+    try:
+        yield
+    finally:
+        settings.cache_enabled = original_enabled