Fix message logging for Response API requests (#3226)

* Fix message logging for Response API requests

Response API uses `input` field instead of `messages`. Convert input to
messages format when logging to ensure consistent data across all API types.

* Add unit tests

Author: alexdima

src/extension/prompt/node/chatMLFetcher.ts

@@ -4,6 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { Raw } from '@vscode/prompt-tsx';
+import type { OpenAI } from 'openai';
 import type { CancellationToken } from 'vscode';
 import { IAuthenticationService } from '../../../platform/authentication/common/authentication';
 import { CopilotToken } from '../../../platform/authentication/common/copilotToken';
@@ -14,14 +15,15 @@ import { IConversationOptions } from '../../../platform/chat/common/conversation
 import { getTextPart, toTextParts } from '../../../platform/chat/common/globalStringUtils';
 import { IInteractionService } from '../../../platform/chat/common/interactionService';
 import { ConfigKey, HARD_TOOL_LIMIT, IConfigurationService } from '../../../platform/configuration/common/configurationService';
-import { isAnthropicToolSearchEnabled } from '../../../platform/networking/common/anthropic';
 import { ICAPIClientService } from '../../../platform/endpoint/common/capiClient';
 import { isAutoModel } from '../../../platform/endpoint/node/autoChatEndpoint';
+import { responseApiInputToRawMessagesForLogging } from '../../../platform/endpoint/node/responsesApi';
 import { collectSingleLineErrorMessage, ILogService } from '../../../platform/log/common/logService';
+import { isAnthropicToolSearchEnabled } from '../../../platform/networking/common/anthropic';
 import { FinishedCallback, getRequestId, IResponseDelta, OptionalChatRequestParams } from '../../../platform/networking/common/fetch';
 import { FetcherId, IFetcherService, Response } from '../../../platform/networking/common/fetcherService';
 import { IChatEndpoint, IEndpointBody, postRequest, stringifyUrlOrRequestMetadata } from '../../../platform/networking/common/networking';
-import { CAPIChatMessage, ChatCompletion, FilterReason, FinishedCompletionReason } from '../../../platform/networking/common/openai';
+import { CAPIChatMessage, ChatCompletion, FilterReason, FinishedCompletionReason, rawMessageToCAPI } from '../../../platform/networking/common/openai';
 import { sendEngineMessagesTelemetry } from '../../../platform/networking/node/chatStream';
 import { sendCommunicationErrorTelemetry } from '../../../platform/networking/node/stream';
 import { ChatFailKind, ChatRequestCanceled, ChatRequestFailed, ChatResults, FetchResponseKind } from '../../../platform/openai/node/fetch';
@@ -793,7 +795,20 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 				throw error;
 			})
 			.finally(() => {
-				sendEngineMessagesTelemetry(this._telemetryService, request.messages ?? [], telemetryData, false, this._logService);
+				let messagesToLog = request.messages;
+
+				// For Response API (has input but no messages), convert input to messages for logging
+				if ((!messagesToLog || messagesToLog.length === 0) && (request as OpenAI.Responses.ResponseCreateParams).input) {
+					try {
+						const rawMessages = responseApiInputToRawMessagesForLogging(request as OpenAI.Responses.ResponseCreateParams);
+						messagesToLog = rawMessageToCAPI(rawMessages);
+					} catch (e) {
+						this._logService.error(`Failed to convert Response API input to messages for telemetry:`, e);
+						messagesToLog = [];
+					}
+				}
+
+				sendEngineMessagesTelemetry(this._telemetryService, messagesToLog ?? [], telemetryData, false, this._logService);
 			});
 	}