.NET: [Feature Branch] Migrate state schema updates and support for agents as MCP tools (#1979)

dotnet/src/Microsoft.Agents.AI.DurableTask/State/DurableAgentStateEntry.cs

@@ -0,0 +1,44 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Microsoft.Agents.AI.DurableTask.State;
+
+/// <summary>
+/// Represents a single entry in the durable agent state, which can either be a
+/// user/system request or agent response.
+/// </summary>
+[JsonPolymorphic(TypeDiscriminatorPropertyName = "$type")]
+[JsonDerivedType(typeof(DurableAgentStateRequest), "request")]
+[JsonDerivedType(typeof(DurableAgentStateResponse), "response")]
+internal abstract class DurableAgentStateEntry
+{
+    /// <summary>
+    /// Gets the correlation ID for this entry.
+    /// </summary>
+    /// <remarks>
+    /// This ID is used to correlate <see cref="DurableAgentStateResponse"/> back to its
+    /// <see cref="DurableAgentStateRequest"/>.
+    /// </remarks>
+    [JsonPropertyName("correlationId")]
+    public required string CorrelationId { get; init; }
+
+    /// <summary>
+    /// Gets the timestamp when this entry was created.
+    /// </summary>
+    [JsonPropertyName("createdAt")]
+    public required DateTimeOffset CreatedAt { get; init; }
+
+    /// <summary>
+    /// Gets the list of messages associated with this entry, in chronological order.
+    /// </summary>
+    [JsonPropertyName("messages")]
+    public IReadOnlyList<DurableAgentStateMessage> Messages { get; init; } = [];
+
+    /// <summary>
+    /// Gets any additional data found during deserialization that does not map to known properties.
+    /// </summary>
+    [JsonExtensionData]
+    public IDictionary<string, JsonElement>? ExtensionData { get; set; }
+}