.NET: [BREAKING] Move AgentSession.Serialize to AIAgent (#3650)

* Move AgentSession.Serialize to AIAgent

* Address PR comments.

* Improve code and fix unit test

* Update test agents to return a default json element instead of throwing where the the result of the serialization is never used.

* Update further tests to actually serialize the session

dotnet/samples/GettingStarted/AgentProviders/Agent_With_CustomImplementation/Program.cs

@@ -31,6 +31,16 @@ namespace SampleApp
         public override ValueTask<AgentSession> CreateSessionAsync(CancellationToken cancellationToken = default)
             => new(new CustomAgentSession());
 
+        public override JsonElement SerializeSession(AgentSession session, JsonSerializerOptions? jsonSerializerOptions = null)
+        {
+            if (session is not CustomAgentSession typedSession)
+            {
+                throw new ArgumentException($"The provided session is not of type {nameof(CustomAgentSession)}.", nameof(session));
+            }
+
+            return typedSession.Serialize(jsonSerializerOptions);
+        }
+
         public override ValueTask<AgentSession> DeserializeSessionAsync(JsonElement serializedSession, JsonSerializerOptions? jsonSerializerOptions = null, CancellationToken cancellationToken = default)
             => new(new CustomAgentSession(serializedSession, jsonSerializerOptions));
 
@@ -136,6 +146,9 @@ namespace SampleApp
 
             internal CustomAgentSession(JsonElement serializedSessionState, JsonSerializerOptions? jsonSerializerOptions = null)
                 : base(serializedSessionState, jsonSerializerOptions) { }
+
+            internal new JsonElement Serialize(JsonSerializerOptions? jsonSerializerOptions = null)
+                => base.Serialize(jsonSerializerOptions);
         }
     }
 }

dotnet/samples/GettingStarted/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs

@@ -55,7 +55,7 @@ await Task.Delay(TimeSpan.FromSeconds(2));
 Console.WriteLine(await agent.RunAsync("What do you already know about my upcoming trip?", session));
 
 Console.WriteLine("\n>> Serialize and deserialize the session to demonstrate persisted state\n");
-JsonElement serializedSession = session.Serialize();
+JsonElement serializedSession = agent.SerializeSession(session);
 AgentSession restoredSession = await agent.DeserializeSessionAsync(serializedSession);
 Console.WriteLine(await agent.RunAsync("Can you recap the personal details you remember?", restoredSession));
 

dotnet/samples/GettingStarted/AgentWithMemory/AgentWithMemory_Step03_CustomMemory/Program.cs

@@ -47,7 +47,7 @@ Console.WriteLine(await agent.RunAsync("My name is Ruaidhrí", session));
 Console.WriteLine(await agent.RunAsync("I am 20 years old", session));
 
 // We can serialize the session. The serialized state will include the state of the memory component.
-var sesionElement = session.Serialize();
+JsonElement sesionElement = agent.SerializeSession(session);
 
 Console.WriteLine("\n>> Use deserialized session with previously created memories\n");
 

dotnet/samples/GettingStarted/Agents/Agent_Step06_PersistedConversations/Program.cs

@@ -25,7 +25,7 @@ AgentSession session = await agent.CreateSessionAsync();
 Console.WriteLine(await agent.RunAsync("Tell me a joke about a pirate.", session));
 
 // Serialize the session state to a JsonElement, so it can be stored for later use.
-JsonElement serializedSession = session.Serialize();
+JsonElement serializedSession = agent.SerializeSession(session);
 
 // Save the serialized session to a temporary file (for demonstration purposes).
 string tempFilePath = Path.GetTempFileName();

dotnet/samples/GettingStarted/Agents/Agent_Step07_3rdPartyThreadStorage/Program.cs

@@ -47,7 +47,7 @@ Console.WriteLine(await agent.RunAsync("Tell me a joke about a pirate.", session
 // Serialize the session state, so it can be stored for later use.
 // Since the chat history is stored in the vector store, the serialized session
 // only contains the guid that the messages are stored under in the vector store.
-JsonElement serializedSession = session.Serialize();
+JsonElement serializedSession = agent.SerializeSession(session);
 
 Console.WriteLine("\n--- Serialized session ---\n");
 Console.WriteLine(JsonSerializer.Serialize(serializedSession, new JsonSerializerOptions { WriteIndented = true }));

dotnet/samples/GettingStarted/Agents/Agent_Step13_BackgroundResponsesWithToolsAndPersistence/Program.cs

@@ -40,7 +40,7 @@ AgentResponse response = await agent.RunAsync("Write a very long novel about a t
 // Poll for background responses until complete.
 while (response.ContinuationToken is not null)
 {
-    PersistAgentState(session, response.ContinuationToken);
+    PersistAgentState(agent, session, response.ContinuationToken);
 
     await Task.Delay(TimeSpan.FromSeconds(10));
 
@@ -52,9 +52,9 @@ while (response.ContinuationToken is not null)
 
 Console.WriteLine(response.Text);
 
-void PersistAgentState(AgentSession? session, ResponseContinuationToken? continuationToken)
+void PersistAgentState(AIAgent agent, AgentSession? session, ResponseContinuationToken? continuationToken)
 {
-    stateStore["session"] = session!.Serialize();
+    stateStore["session"] = agent.SerializeSession(session!);
     stateStore["continuationToken"] = JsonSerializer.SerializeToElement(continuationToken, AgentAbstractionsJsonUtilities.DefaultOptions.GetTypeInfo(typeof(ResponseContinuationToken)));
 }
 

dotnet/samples/GettingStarted/Agents/Agent_Step20_AdditionalAIContext/Program.cs

@@ -65,7 +65,7 @@ Console.WriteLine(await agent.RunAsync("I need to make a dentist appointment for
 Console.WriteLine(await agent.RunAsync("I've taken Sally to soccer practice.", session) + "\n");
 
 // We can serialize the session, and it will contain both the chat history and the data that each AI context provider serialized.
-JsonElement serializedSession = session.Serialize();
+JsonElement serializedSession = agent.SerializeSession(session);
 // Let's print it to console to show the contents.
 Console.WriteLine(JsonSerializer.Serialize(serializedSession, options: new JsonSerializerOptions() { WriteIndented = true, IndentSize = 2 }) + "\n");
 // The serialized session can be stored long term in a persistent store, but in this case we will just deserialize again and continue the conversation.

dotnet/samples/GettingStarted/FoundryAgents/FoundryAgents_Step06_PersistedConversations/Program.cs

@@ -25,7 +25,7 @@ AgentSession session = await agent.CreateSessionAsync();
 Console.WriteLine(await agent.RunAsync("Tell me a joke about a pirate.", session));
 
 // Serialize the session state to a JsonElement, so it can be stored for later use.
-JsonElement serializedSession = session.Serialize();
+JsonElement serializedSession = agent.SerializeSession(session);
 
 // Save the serialized session to a temporary file (for demonstration purposes).
 string tempFilePath = Path.GetTempFileName();