test(config): verify runtime persistence safety

src/test/java/games/dmg/leaf/LeafRuntimeTest.java

@@ -128,6 +128,29 @@ final class LeafRuntimeTest {
         verify(identity, org.mockito.Mockito.atLeastOnce()).remove(player);
     }
 
+    @Test
+    void doesNotActivateASettingWhenItsPersistenceFails() throws Exception {
+        Server server = mock(Server.class);
+        LeafSettingsProvider settings = new LeafSettingsProvider(LeafSettings.from(Map.of()));
+        LeafRuntime runtime = new LeafRuntime(
+            server,
+            settings,
+            new LeafStateManager(new YamlLeafStateRepository(
+                temporaryDirectory.resolve("failed-settings.yml")
+            )),
+            mock(LeafProtection.class),
+            mock(LeafIdentity.class),
+            replacement -> {
+                throw new java.io.IOException("disk unavailable");
+            }
+        );
+
+        assertThrows(java.io.IOException.class, () -> runtime.setGlobalEnabled(false));
+
+        assertTrue(settings.current().enabled());
+        verify(server, never()).getOnlinePlayers();
+    }
+
     @Test
     void resolvesLatestPreviousNamesAndUuidsWithoutGuessingAmbiguities() throws Exception {
         Server server = mock(Server.class);

src/test/java/games/dmg/leaf/LeafStateManagerTest.java

@@ -27,5 +27,6 @@ final class LeafStateManagerTest {
         PlayerLeafState saved = repository.load().players().get(playerId);
         assertEquals(first, saved.firstJoin());
         assertEquals("AlexNew", saved.latestName());
+        assertEquals(java.util.Set.of("Alex", "AlexNew"), saved.knownNames());
     }
 }