Lazy clock reads; demo: auto-advancing +1h clock, module-level setup

tests/test_clock.py

@@ -72,6 +72,27 @@ async def test_clock_controls_record_timestamps(tmp_path, format_config):
     assert kanta.mtime == T0 + timedelta(hours=1)
 
 
+@pytest.mark.asyncio
+async def test_clock_not_read_without_changes(tmp_path, format_config):
+    kanta = make_kanta(tmp_path / "test.db", Data, format_config)
+    reads = 0
+
+    @kanta.clock
+    def fake_now() -> datetime:
+        nonlocal reads
+        reads += 1
+        return T0
+
+    await kanta.open(log=False)  # bootstrap record: one read
+    reads = 0
+
+    with kanta.transaction(action="noop"):
+        pass  # no changes, no record, no clock read
+    await kanta.close()  # no snapshot written, no clock read
+
+    assert reads == 0
+
+
 @pytest.mark.asyncio
 async def test_clock_controls_migration_and_snapshot_timestamps(
     tmp_path, format_config