.NET: [Bug]: MissingMethodException in ProcessDataContentAttachmentsAsync due to binary incompatibility with GitHub.Copilot.SDK

[normalian]

Description

When using the NuGet package Microsoft.Agents.AI.GitHub.Copilot (version 1.0.0-preview.260209.1), a MissingMethodException occurs when sending messages with attachments.

Code Sample

using GitHub.Copilot.SDK;
using Microsoft.Agents.AI;
using Microsoft.Agents.AI.GitHub.Copilot;
using Microsoft.Extensions.AI;

using var copilotClient = new CopilotClient();
var config = new SessionConfig { Model = "claude-3.5-sonnet" };
var agent = new GitHubCopilotAgent(copilotClient, config);

await agent.CreateSessionAsync();

string filePath = "Program.cs"; 
byte[] fileBytes = await File.ReadAllBytesAsync(filePath);
string mimeType = "text/plain"; 

var message = new ChatMessage(ChatRole.User, "What's the best practice to test private methods?");

message.Contents.Add(new DataContent(fileBytes, mimeType));

var messages = new List<ChatMessage> { message };

try
{
    Console.WriteLine($"Sending message with attachment: {filePath}...");
    var response = await agent.RunAsync(messages);
    Console.WriteLine("--- Agent Response ---");
    Console.WriteLine(response);
}
catch (Exception ex)
{
    Console.WriteLine($"Error: {ex.Message}");
    if (ex.InnerException != null)
        Console.WriteLine($"Inner: {ex.InnerException.Message}");
}

Error Messages / Stack Traces

Method not found: 'Void GitHub.Copilot.SDK.UserMessageDataAttachmentsItem.set_Type(GitHub.Copilot.SDK.UserMessageDataAttachmentsItemType)'.
at Microsoft.Agents.AI.GitHub.Copilot.GitHubCopilotAgent.<ProcessDataContentAttachmentsAsync>d__33.MoveNext()

Package Versions

Microsoft.Agents.AI.GitHub.Copilot: 1.0.0-preview.260209.1

.NET Version

.NET 9.0

Additional Context

Investigation
The Cause: The property UserMessageDataAttachmentsItem.Type in the latest GitHub.Copilot.SDK appears to have changed its setter (e.g., from set to init), breaking binary compatibility with the pre-compiled NuGet package.

Evidence: - Using the NuGet package results in the error above.

However, cloning this repository and referencing the source code directly works perfectly, because the code is re-compiled against the latest SDK during the local build.