Fix Assistants IChatClient handling of unrelated tool calls in history (#6891)

The implementation is assuming that any tool results in the incoming message history mean a thread ID is required, which would be necessary if those tool results were for an active run. But that's not the case if the history just contains historical function calls/responses, as is the case in agent scenarios where the message history from one agent is passed to another.  The fix is to just stop throwing based on this incorrect assumption.

Author: stephentoub

src/Libraries/Microsoft.Extensions.AI.OpenAI/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## NOT YET RELEASED
 
+- Fixed issue with IChatClient for Assistants API where a chat history including unrelated function calls would cause an exception.
+
 ## 9.9.1-preview.1.25474.6
 
 - Updated to depend on OpenAI 2.5.0.

src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIAssistantsChatClient.cs

@@ -80,14 +80,10 @@ public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
 
         // Get the thread ID.
         string? threadId = options?.ConversationId ?? _defaultThreadId;
-        if (threadId is null && toolResults is not null)
-        {
-            Throw.ArgumentException(nameof(messages), "No thread ID was provided, but chat messages includes tool results.");
-        }
 
         // Get any active run ID for this thread. This is necessary in case a thread has been left with an
-        // active run, in which all attempts other than submitting tools will fail. We thus need to cancel
-        // any active run on the thread.
+        // active run, in which case all attempts other than submitting tools will fail. We thus need to cancel
+        // any active run on the thread if we're not submitting tool results to it.
         ThreadRun? threadRun = null;
         if (threadId is not null)
         {
@@ -111,7 +107,7 @@ public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
             ConvertFunctionResultsToToolOutput(toolResults, out List<ToolOutput>? toolOutputs) is { } toolRunId &&
             toolRunId == threadRun.Id)
         {
-            // There's an active run and we have tool results to submit, so submit the results and continue streaming.
+            // There's an active run and, critically, we have tool results to submit for that exact run, so submit the results and continue streaming.
             // This is going to ignore any additional messages in the run options, as we are only submitting tool outputs,
             // but there doesn't appear to be a way to submit additional messages, and having such additional messages is rare.
             updates = _client.SubmitToolOutputsToRunStreamingAsync(threadRun.ThreadId, threadRun.Id, toolOutputs, cancellationToken);
@@ -487,7 +483,7 @@ void AppendSystemInstructions(string? toAppend)
                         messageContents.Add(MessageContent.FromImageUri(image.Uri));
                         break;
 
-                    case FunctionResultContent result:
+                    case FunctionResultContent result when chatMessage.Role == ChatRole.Tool:
                         (functionResults ??= []).Add(result);
                         break;
                 }