test(free-battle): force_finish no-op returns empty object

SVSim.UnitTests/Controllers/FreeBattleControllerTests.cs

@@ -151,4 +151,22 @@ public class FreeBattleControllerTests
         using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
         Assert.That(doc.RootElement.GetProperty("battle_result").GetInt32(), Is.EqualTo(2));
     }
+
+    [Test]
+    public async Task ForceFinish_returns_200_with_empty_object()
+    {
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync();
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/free_battle/force_finish", EmptyAuthedBody);
+
+        Assert.That(resp.IsSuccessStatusCode, Is.True);
+        var raw = await resp.Content.ReadAsStringAsync();
+        using var doc = JsonDocument.Parse(raw);
+        Assert.That(doc.RootElement.ValueKind, Is.EqualTo(JsonValueKind.Object));
+        // Empty object: no enumerable properties.
+        Assert.That(doc.RootElement.EnumerateObject().MoveNext(), Is.False,
+            "Body should be {} — defensive no-op for dead URL.");
+    }
 }