chore: import upstream snapshot with attribution

dotnet/samples/02-agents/AgentProviders/foundry/Agent_Step24_CodeInterpreterFileDownload/Agent_Step24_CodeInterpreterFileDownload.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net10.0</TargetFrameworks>
+
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Azure.Identity" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\..\src\Microsoft.Agents.AI.Foundry\Microsoft.Agents.AI.Foundry.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/samples/02-agents/AgentProviders/foundry/Agent_Step24_CodeInterpreterFileDownload/Program.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample shows how to download files generated by Code Interpreter using Microsoft Foundry.
+// Code Interpreter generates files inside containers (cfile_ / cntr_ IDs) which cannot be
+// downloaded via the standard Files API. Use ContainerClient from the project's OpenAI client instead.
+
+#pragma warning disable OPENAI001
+
+using Azure.AI.Projects;
+using Azure.Identity;
+using Microsoft.Agents.AI;
+using Microsoft.Extensions.AI;
+using OpenAI.Responses;
+
+string endpoint = Environment.GetEnvironmentVariable("FOUNDRY_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("FOUNDRY_PROJECT_ENDPOINT is not set.");
+string deploymentName = Environment.GetEnvironmentVariable("FOUNDRY_MODEL") ?? "gpt-4o-mini";
+
+// WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
+// In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
+// latency issues, unintended credential probing, and potential security risks from fallback mechanisms.
+AIProjectClient aiProjectClient = new(new Uri(endpoint), new DefaultAzureCredential());
+
+// Create an agent with Code Interpreter tool enabled
+AIAgent agent = aiProjectClient.AsAIAgent(
+    deploymentName,
+    instructions: "You are a helpful assistant that can generate files using code.",
+    name: "CodeInterpreterAgent",
+    tools: [new HostedCodeInterpreterTool()]);
+
+// Ask the agent to generate a file
+AgentResponse response = await agent.RunAsync(
+    "Create a CSV file with the multiplication times tables from 1 to 12. Include headers.");
+
+// Display the text response
+foreach (TextContent textContent in response.Messages.SelectMany(x => x.Contents).OfType<TextContent>())
+{
+    Console.WriteLine(textContent.Text);
+}
+
+// Extract container file citations from response annotations and download.
+// AIProjectClient.GetProjectOpenAIClient() returns a ProjectOpenAIClient (inherits from OpenAI.OpenAIClient)
+// which supports GetContainerClient(), unlike AzureOpenAIClient which does not.
+var containerClient = aiProjectClient.GetProjectOpenAIClient().GetContainerClient();
+
+HashSet<string> downloadedFiles = [];
+bool foundContainerFiles = false;
+
+foreach (AIContent content in response.Messages.SelectMany(x => x.Contents))
+{
+    if (content.Annotations is null)
+    {
+        continue;
+    }
+
+    foreach (AIAnnotation annotation in content.Annotations)
+    {
+        // Container files from Code Interpreter have ContainerFileCitationMessageAnnotation as raw representation
+        if (annotation is CitationAnnotation citation
+            && citation.RawRepresentation is ContainerFileCitationMessageAnnotation containerCitation)
+        {
+            foundContainerFiles = true;
+
+            // Deduplicate by container+file ID in case the same file is cited multiple times
+            string key = $"{containerCitation.ContainerId}/{containerCitation.FileId}";
+            if (!downloadedFiles.Add(key))
+            {
+                continue;
+            }
+
+            Console.WriteLine($"\nDownloading container file: {containerCitation.Filename}");
+            Console.WriteLine($"  Container ID: {containerCitation.ContainerId}");
+            Console.WriteLine($"  File ID:      {containerCitation.FileId}");
+
+            BinaryData fileData = await containerClient.DownloadContainerFileAsync(
+                containerCitation.ContainerId,
+                containerCitation.FileId);
+
+            // Sanitize filename to prevent path traversal
+            string safeFilename = Path.GetFileName(containerCitation.Filename);
+            string outputPath = Path.Combine(Directory.GetCurrentDirectory(), safeFilename);
+            await File.WriteAllBytesAsync(outputPath, fileData.ToArray());
+            Console.WriteLine($"  Saved to:     {outputPath}");
+        }
+    }
+}
+
+if (!foundContainerFiles)
+{
+    Console.WriteLine("\nNo container file citations found in the response.");
+    Console.WriteLine("The model may not have generated a downloadable file for this prompt.");
+}

dotnet/samples/02-agents/AgentProviders/foundry/Agent_Step24_CodeInterpreterFileDownload/README.md

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+# Code Interpreter File Download (Microsoft Foundry)
+
+This sample demonstrates how to download files generated by Code Interpreter when using Microsoft Foundry.
+
+## What this sample demonstrates
+
+- Creating an agent with Code Interpreter tool using `AIProjectClient.AsAIAgent()`
+- Generating files through Code Interpreter (e.g., CSV, Excel, images)
+- Extracting container file citations from agent response annotations
+- Downloading container files using the `ContainerClient` via `AIProjectClient.GetProjectOpenAIClient()`
+
+## Container files vs regular files
+
+When Code Interpreter generates a file, the file is stored inside a **container** with a `cntr_` prefixed ID. The file itself gets a `cfile_` prefixed ID.
+
+These container files **cannot** be downloaded using the standard Files API (`GetOpenAIFileClient`), which returns 404 for `cfile_` IDs. Instead, you must use the **Containers API** to download them.
+
+### Getting the ContainerClient with Foundry
+
+`AzureOpenAIClient.GetContainerClient()` is not supported and throws `InvalidOperationException`. Instead, use the project's OpenAI client which inherits directly from `OpenAI.OpenAIClient`:
+
+```csharp
+// ❌ AzureOpenAIClient does not support ContainerClient
+var azureClient = new AzureOpenAIClient(endpoint, credential);
+azureClient.GetContainerClient();  // Throws InvalidOperationException
+
+// ✅ Use AIProjectClient's project OpenAI client
+var containerClient = aiProjectClient.GetProjectOpenAIClient().GetContainerClient();
+await containerClient.DownloadContainerFileAsync("cntr_...", "cfile_...");
+```
+
+The container ID and file ID are available from the `ContainerFileCitationMessageAnnotation` annotation in the response, accessible via `CitationAnnotation.RawRepresentation`.
+
+## Prerequisites
+
+- .NET 10 SDK or later
+- Microsoft Foundry service endpoint and deployment configured
+- An authenticated Azure identity (for example, sign in with `az login`)
+
+Set the following environment variables:
+
+```powershell
+$env:FOUNDRY_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
+$env:FOUNDRY_MODEL="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+```
+
+## Run the sample
+
+```powershell
+dotnet run
+```
+
+## See also
+
+- [Code Interpreter File Download with OpenAI](../../openai/Agent_OpenAI_Step06_CodeInterpreterFileDownload/) — same scenario using Public OpenAI
+- [Code Interpreter](../Agent_Step14_CodeInterpreter/) — Code Interpreter without file download
+