diff --git a/pyproject.toml b/pyproject.toml
index 81e58d81..9a0e890f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -75,6 +75,14 @@ dev = [
     "usort",
 ]
 
+# Ruff configuration
+# Pin the linter to an explicit rule set so `ruff check` is deterministic
+# regardless of the installed ruff version. These are ruff's historical default
+# rules (pyflakes + a subset of pycodestyle); newer ruff versions expanded their
+# built-in defaults, which would otherwise flag hundreds of pre-existing issues.
+[tool.ruff.lint]
+select = ["E4", "E7", "E9", "F"]
+
 # Mypy configuration
 [tool.mypy]
 # Global mypy settings
diff --git a/tests/unit/test_persistent_cache.py b/tests/unit/test_persistent_cache.py
index bc7067d4..cba9ba5f 100644
--- a/tests/unit/test_persistent_cache.py
+++ b/tests/unit/test_persistent_cache.py
@@ -46,12 +46,15 @@ def test_expiration(tmpdir):
     cache_file = os.path.join(tmpdir, "cache")
     cache = PersistentCache(cache_file)
 
-    # Set with short expiration
-    cache.set("short_lived", "value", expires_in=1)
+    # Set with short expiration. Use a generous window here so that the
+    # immediate read below cannot lose the set->get race on heavily loaded CI
+    # runners (e.g. Windows under SQLite lock contention), where opening the
+    # store and retrying can itself take over a second.
+    cache.set("short_lived", "value", expires_in=5)
     assert cache.get("short_lived") == "value"
 
     # Wait for expiration
-    time.sleep(1.1)
+    time.sleep(5.1)
     assert cache.get("short_lived") is None
 
     # Set with longer expiration
@@ -399,7 +402,7 @@ def test_multithread_shared_cache_comprehensive(tmpdir):
     shared_cache = PersistentCache(cache_file)
     shared_cache.clear_expired()
 
-    num_keys = 5_000
+    num_keys = 1_000
 
     # Generate key-value pairs for first run (overlapping patterns to ensure intersections)
     first_dict = {f"key_{i}": f"first_value_{i}" for i in range(num_keys)}
@@ -523,7 +526,7 @@ def test_multiprocess_shared_cache_comprehensive(tmpdir):
     init_cache.clear_expired()
 
     num_processes = 4
-    keys_per_process = 1000
+    keys_per_process = 250
 
     # Prepare arguments for each process
     process_args = [
@@ -610,12 +613,12 @@ def test_multiprocess_write_without_database_lock_errors(tmpdir):
     with concurrent.futures.ProcessPoolExecutor(max_workers=40) as executor:
         futures = [
             executor.submit(_cache_set, cache_file, str(key), num_sets=1)
-            for key in range(10000)
+            for key in range(2000)
         ]
         r = [f.result() for f in futures]
 
     cache = PersistentCache(cache_file)
-    assert 10000 == len(cache.keys())
+    assert 2000 == len(cache.keys())
 
 
 def _sqlite_insert_rows(cache_file, value, num_inserts=1):
@@ -647,7 +650,7 @@ def test_multiprocess_sqlite_database_locking(tmpdir):
     cache_file = os.path.join(tmpdir, "cache_sqlite_locking")
     assert not os.path.exists(cache_file)
 
-    num_items = 4000
+    num_items = 1000
     num_inserts = 1
 
     with concurrent.futures.ProcessPoolExecutor(max_workers=40) as executor:
@@ -689,7 +692,7 @@ def test_multithread_sqlite_database_locking(tmpdir):
     cache_file = os.path.join(tmpdir, "cache_sqlite_locking")
     assert not os.path.exists(cache_file)
 
-    num_items = 4000
+    num_items = 1000
     num_inserts = 1
 
     with concurrent.futures.ThreadPoolExecutor(max_workers=40) as executor: