.Net - Updated Open AI Assistant Model Serialization (#5102)

### Motivation and Context

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Certain model properties not serializing properly due to definition
alignment.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

`Agent === Assistant` when dealing with Open AI models.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Co-authored-by: Mark Wallace <127216156+markwallace-microsoft@users.noreply.github.com>

dotnet/src/Experimental/Agents/Internal/ChatMessage.cs

@@ -40,7 +40,7 @@ internal ChatMessage(ThreadMessageModel model)
         this.Annotations = content.Text!.Annotations.Select(a => new Annotation(a.Text, a.StartIndex, a.EndIndex, a.FileCitation?.FileId ?? a.FilePath!.FileId, a.FileCitation?.Quote)).ToArray();
 
         this.Id = model.Id;
-        this.AgentId = string.IsNullOrWhiteSpace(model.AgentId) ? null : model.AgentId;
+        this.AgentId = string.IsNullOrWhiteSpace(model.AssistantId) ? null : model.AssistantId;
         this.Role = model.Role;
         this.Content = text;
         this.Properties = new ReadOnlyDictionary<string, object>(model.Metadata);

dotnet/src/Experimental/Agents/Internal/ChatRun.cs

@@ -22,7 +22,7 @@ internal sealed class ChatRun
     public string Id => this._model.Id;
 
     /// <inheritdoc/>
-    public string AgentId => this._model.AgentId;
+    public string AgentId => this._model.AssistantId;
 
     /// <inheritdoc/>
     public string ThreadId => this._model.ThreadId;

dotnet/src/Experimental/Agents/Models/ThreadMessageModel.cs

@@ -39,7 +39,7 @@ internal sealed class ThreadMessageModel
     public string ThreadId { get; set; } = string.Empty;
 
     /// <summary>
-    /// The entity that produced the message. One of "user" or "agent".
+    /// The entity that produced the message. One of "user" or "assistant".
     /// </summary>
     [JsonPropertyName("role")]
     public string Role { get; set; } = string.Empty;
@@ -57,10 +57,10 @@ internal sealed class ThreadMessageModel
     public List<string> FileIds { get; set; } = new List<string>();
 
     /// <summary>
-    /// If applicable, the ID of the agent that authored this message.
+    /// If applicable, the ID of the assistant that authored this message.
     /// </summary>
-    [JsonPropertyName("agent_id")]
-    public string AgentId { get; set; } = string.Empty;
+    [JsonPropertyName("assistant_id")]
+    public string AssistantId { get; set; } = string.Empty;
 
     /// <summary>
     /// If applicable, the ID of the run associated with the authoring of this message.

dotnet/src/Experimental/Agents/Models/ThreadRunModel.cs

@@ -24,10 +24,10 @@ internal sealed class ThreadRunModel
     public long CreatedAt { get; set; }
 
     /// <summary>
-    /// ID of the agent used for execution of this run.
+    /// ID of the assistant used for execution of this run.
     /// </summary>
-    [JsonPropertyName("agent_id")]
-    public string AgentId { get; set; } = string.Empty;
+    [JsonPropertyName("assistant_id")]
+    public string AssistantId { get; set; } = string.Empty;
 
     /// <summary>
     /// ID of the thread that was executed on as a part of this run.
@@ -79,25 +79,25 @@ internal sealed class ThreadRunModel
     public ErrorModel? LastError { get; set; }
 
     /// <summary>
-    /// The model that the agent used for this run.
+    /// The model that the assistant used for this run.
     /// </summary>
     [JsonPropertyName("model")]
     public string Model { get; set; } = string.Empty;
 
     /// <summary>
-    /// The instructions that the agent used for this run.
+    /// The instructions that the assistant used for this run.
     /// </summary>
     [JsonPropertyName("instructions")]
     public string Instructions { get; set; } = string.Empty;
 
     /// <summary>
-    /// The list of tools that the agent used for this run.
+    /// The list of tools that the assistant used for this run.
     /// </summary>
     [JsonPropertyName("tools")]
     public List<ToolModel> Tools { get; set; } = new List<ToolModel>();
 
     /// <summary>
-    /// The list of File IDs the agent used for this run.
+    /// The list of File IDs the assistant used for this run.
     /// </summary>
     [JsonPropertyName("file_ids")]
     public List<string> FileIds { get; set; } = new List<string>();

dotnet/src/Experimental/Agents/Models/ThreadRunStepModel.cs

@@ -38,10 +38,10 @@ internal sealed class ThreadRunStepModel
     public string RunId { get; set; } = string.Empty;
 
     /// <summary>
-    /// ID of the agent associated with the run step.
+    /// ID of the assistant associated with the run step.
     /// </summary>
-    [JsonPropertyName("agent_id")]
-    public string AgentId { get; set; } = string.Empty;
+    [JsonPropertyName("assistant_id")]
+    public string AssistantId { get; set; } = string.Empty;
 
     /// <summary>
     /// The ID of the thread to which the run and run step belongs.