.NET: Fix FoundryAgents_Step15_ComputerUse sample for Azure Agents API (#3989)

* Fix FoundryAgents_Step15_ComputerUse sample for Azure Agents API

The Azure Agents API rejects previous_response_id alongside computer_call_output
items, unlike the vanilla OpenAI Responses API. This fix:

- Send all prior response output items (reasoning, computer_call, etc.) as input
  items in follow-up calls so the API has full conversation context
- Create a fresh session per call to avoid ConversationId/previous_response_id
- Use currentCallId instead of initialCallId for computer_call_output
- Clear ContinuationToken after polling to prevent stale tokens
- Remove unused initialCallId tracking variable

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address comments

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet/samples/GettingStarted/FoundryAgents/FoundryAgents_Step15_ComputerUse/Program.cs

@@ -86,8 +86,6 @@ internal sealed class Program
             AllowBackgroundResponses = true,
         };
 
-        AgentSession session = await agent.CreateSessionAsync();
-
         ChatMessage message = new(ChatRole.User, [
             new TextContent("I need you to help me search for 'OpenAI news'. Please type 'OpenAI news' and submit the search. Once you see search results, the task is complete."),
             new DataContent(new BinaryData(screenshots["browser_search"]), "image/png")
@@ -96,6 +94,11 @@ internal sealed class Program
         // Initial request with screenshot - start with Bing search page
         Console.WriteLine("Starting computer automation session (initial screenshot: cua_browser_search.png)...");
 
+        // IMPORTANT: Computer-use with the Azure Agents API differs from the vanilla OpenAI Responses API.
+        // The Azure Agents API rejects requests that include previous_response_id alongside
+        // computer_call_output items. To work around this, each call uses a fresh session (avoiding
+        // previous_response_id) and re-sends the full conversation context as input items instead.
+        AgentSession session = await agent.CreateSessionAsync();
         AgentResponse response = await agent.RunAsync(message, session: session, options: runOptions);
 
         // Main interaction loop
@@ -103,7 +106,6 @@ internal sealed class Program
         int iteration = 0;
         // Initialize state machine
         SearchState currentState = SearchState.Initial;
-        string initialCallId = string.Empty;
 
         while (true)
         {
@@ -119,6 +121,9 @@ internal sealed class Program
                 response = await agent.RunAsync(session, runOptions);
             }
 
+            // Clear the continuation token so the next RunAsync call is a fresh request.
+            runOptions.ContinuationToken = null;
+
             Console.WriteLine($"Agent response received (ID: {response.ResponseId})");
 
             if (iteration >= MaxIterations)
@@ -148,12 +153,6 @@ internal sealed class Program
             ComputerCallAction action = firstComputerCall.Action;
             string currentCallId = firstComputerCall.CallId;
 
-            // Set the initial computer call ID for tracking and subsequent responses.
-            if (string.IsNullOrEmpty(initialCallId))
-            {
-                initialCallId = currentCallId;
-            }
-
             Console.WriteLine($"Processing computer call (ID: {currentCallId})");
 
             // Simulate executing the action and taking a screenshot
@@ -162,16 +161,31 @@ internal sealed class Program
 
             Console.WriteLine("Sending action result back to agent...");
 
-            AIContent content = new()
+            // Build the follow-up messages with full conversation context.
+            // The Azure Agents API rejects previous_response_id when computer_call_output items are
+            // present, so we must re-send all prior output items (reasoning, computer_call, etc.)
+            // as input items alongside the computer_call_output to maintain conversation continuity.
+            List<ChatMessage> followUpMessages = [];
+
+            // Re-send all response output items as an assistant message so the API has full context
+            List<AIContent> priorOutputContents = response.Messages
+                .SelectMany(m => m.Contents)
+                .ToList();
+            followUpMessages.Add(new ChatMessage(ChatRole.Assistant, priorOutputContents));
+
+            // Add the computer_call_output as a user message
+            AIContent callOutput = new()
             {
                 RawRepresentation = new ComputerCallOutputResponseItem(
-                    initialCallId,
+                    currentCallId,
                     output: ComputerCallOutput.CreateScreenshotOutput(new BinaryData(screenInfo.ImageBytes), "image/png"))
             };
+            followUpMessages.Add(new ChatMessage(ChatRole.User, [callOutput]));
 
-            // Follow-up message with action result and new screenshot
-            message = new(ChatRole.User, [content]);
-            response = await agent.RunAsync(message, session: session, options: runOptions);
+            // Create a fresh session so ConversationId does not carry over a previous_response_id.
+            // Without this, the Azure Agents API returns an error when computer_call_output is present.
+            session = await agent.CreateSessionAsync();
+            response = await agent.RunAsync(followUpMessages, session: session, options: runOptions);
         }
     }
 }

dotnet/samples/GettingStarted/FoundryAgents/FoundryAgents_Step15_ComputerUse/README.md

@@ -2,6 +2,17 @@
 
 This sample demonstrates how to use the computer use tool with AI agents. The computer use tool allows agents to interact with a computer environment by viewing the screen, controlling the mouse and keyboard, and performing various actions to help complete tasks.
 
+> [!NOTE]
+> **Azure Agents API vs. vanilla OpenAI Responses API behavior:**
+> The Azure Agents API rejects requests that include `previous_response_id` alongside
+> `computer_call_output` items — unlike the vanilla OpenAI Responses API, which accepts them.
+> This sample works around the limitation by creating a **fresh session for each follow-up call**
+> (so no `previous_response_id` is carried over) and re-sending all prior response output items
+> (reasoning, computer_call, etc.) as input items to preserve full conversation context.
+> Additionally, the sample uses the **current** `CallId` from each computer call response
+> (not the initial one) and clears the `ContinuationToken` after polling completes to prevent
+> stale tokens from affecting subsequent requests.
+
 ## What this sample demonstrates
 
 - Creating agents with computer use capabilities