Fixed chats not loading in the v26.10.1 pre-release and added a trim smoke test (#1128)

app/TrimSmokeTest/JsonRoundTrips.cs

@@ -0,0 +1,64 @@
+using System.Text.Json;
+
+using AIStudio.Assistants.VisualBriefing;
+using AIStudio.Chat;
+using AIStudio.Settings;
+using AIStudio.Settings.DataModel;
+using AIStudio.Tools;
+
+namespace AIStudio.TrimSmokeTest;
+
+/// <summary>
+/// Writes and reads filled values of the roots which matter most, since some parts of a contract only come
+/// into play once there is a value, e.g., the factory which builds an immutable collection.
+/// </summary>
+public static class JsonRoundTrips
+{
+    private const string TEXT_WITH_WEB_ADDRESS = "The details are on https://example.org/chosen.";
+
+    /// <summary>
+    /// Returns a description of every value which does not survive being written and read again.
+    /// </summary>
+    /// <returns>One line per failure, naming the type which failed.</returns>
+    public static IReadOnlyList<string> FindLosses()
+    {
+        var restrictions = ChatRestrictions.NONE.WithWebAddressesWrittenByModelIn(TEXT_WITH_WEB_ADDRESS);
+        var chat = new ChatThread
+        {
+            Name = "Trim smoke test",
+            Blocks =
+            [
+                new ContentBlock
+                {
+                    Time = DateTimeOffset.UnixEpoch,
+                    ContentType = ContentType.TEXT,
+                    Content = new ContentText { Text = TEXT_WITH_WEB_ADDRESS },
+                    Role = ChatRole.USER,
+                },
+            ],
+        };
+
+        chat.RequireRestrictions(restrictions);
+
+        var failures = new List<string>();
+        AddLoss(chat, WorkspaceBehaviour.JSON_OPTIONS, failures);
+        AddLoss(new Data(), SettingsManager.JSON_OPTIONS, failures);
+        AddLoss(new VisualBriefingManifest { Name = "Trim smoke test", Restrictions = restrictions }, VisualBriefingJson.Persistence, failures);
+        return failures;
+    }
+
+    private static void AddLoss<T>(T value, JsonSerializerOptions options, List<string> failures)
+    {
+        try
+        {
+            var json = JsonSerializer.Serialize(value, options);
+            var jsonAgain = JsonSerializer.Serialize(JsonSerializer.Deserialize<T>(json, options), options);
+            if (jsonAgain != json)
+                failures.Add($"{typeof(T).Name}: written again after reading, it gives other JSON than before.");
+        }
+        catch (Exception exception) when (exception is NotSupportedException or InvalidOperationException or JsonException)
+        {
+            failures.Add($"{typeof(T).Name}: {exception.Message}");
+        }
+    }
+}