refactor(proxy): internalize sse translation and cleanup handlers

src/cursor/cursor-anthropic-response.ts

@@ -1,249 +1,4 @@
-import { DeltaAccumulator } from '../glmt/delta-accumulator';
-import { GlmtTransformer } from '../glmt/glmt-transformer';
-import { SSEParser } from '../glmt/sse-parser';
-import type { OpenAIResponse, SSEEvent } from '../glmt/pipeline';
-
-const JSON_TRANSLATION_ERROR_MESSAGE = 'Failed to translate Cursor JSON response';
-const STREAM_TRANSLATION_ERROR_MESSAGE = 'Failed to translate Cursor SSE response';
-type ResponseHeaders = Headers | Record<string, string> | Array<[string, string]>;
-
-interface AnthropicErrorPayload {
-  type: 'error';
-  error: {
-    type: string;
-    message: string;
-  };
-}
-
-function createAnthropicErrorPayload(type: string, message: string): AnthropicErrorPayload {
-  return {
-    type: 'error',
-    error: {
-      type,
-      message,
-    },
-  };
-}
-
-function formatErrorForLog(error: unknown): string {
-  if (error instanceof Error) {
-    return error.message;
-  }
-
-  try {
-    return JSON.stringify(error);
-  } catch {
-    return String(error);
-  }
-}
-
-function logTranslationError(context: string, error: unknown): void {
-  console.error(`[cursor-anthropic-response] ${context}: ${formatErrorForLog(error)}`);
-}
-
-export function createAnthropicErrorResponse(
-  status: number,
-  type: string,
-  message: string,
-  headers?: ResponseHeaders
-): Response {
-  const responseHeaders = new Headers(headers);
-  responseHeaders.set('Content-Type', 'application/json');
-  responseHeaders.delete('Content-Length');
-
-  return new Response(JSON.stringify(createAnthropicErrorPayload(type, message)), {
-    status,
-    headers: responseHeaders,
-  });
-}
-
-function formatSseEvent(event: string, data: unknown): string {
-  return `event: ${event}\ndata: ${JSON.stringify(data)}\n\n`;
-}
-
-function hasTranslatableChoices(value: unknown): value is OpenAIResponse {
-  if (typeof value !== 'object' || value === null) {
-    return false;
-  }
-
-  const { choices } = value as OpenAIResponse;
-  if (!Array.isArray(choices) || choices.length === 0) {
-    return false;
-  }
-
-  const firstChoice = choices[0];
-  if (typeof firstChoice !== 'object' || firstChoice === null) {
-    return false;
-  }
-
-  const message = (firstChoice as { message?: unknown }).message;
-  return typeof message === 'object' && message !== null;
-}
-
-function isSyntheticTransformationFallback(value: unknown): boolean {
-  return (
-    typeof value === 'object' &&
-    value !== null &&
-    typeof (value as { id?: unknown }).id === 'string' &&
-    (value as { id: string }).id.startsWith('msg_error_')
-  );
-}
-
-async function createAnthropicErrorProxyResponse(response: Response): Promise<Response> {
-  const headers = new Headers(response.headers);
-  headers.delete('Content-Type');
-  headers.delete('Content-Length');
-
-  let type =
-    response.status === 401
-      ? 'authentication_error'
-      : response.status === 429
-        ? 'rate_limit_error'
-        : response.status >= 400 && response.status < 500
-          ? 'invalid_request_error'
-          : 'api_error';
-  let message = `Cursor request failed with status ${response.status}`;
-
-  try {
-    const contentType = (response.headers.get('content-type') || '').toLowerCase();
-    if (contentType.includes('application/json')) {
-      const payload = (await response.json()) as {
-        error?: { type?: string; message?: string };
-        message?: string;
-      };
-
-      if (typeof payload?.error?.type === 'string' && payload.error.type.trim().length > 0) {
-        type = payload.error.type;
-      }
-
-      if (typeof payload?.error?.message === 'string' && payload.error.message.trim().length > 0) {
-        message = payload.error.message;
-      } else if (typeof payload?.message === 'string' && payload.message.trim().length > 0) {
-        message = payload.message;
-      }
-    } else {
-      const text = (await response.text()).trim();
-      if (text.length > 0) {
-        message = text;
-      }
-    }
-  } catch (error) {
-    logTranslationError('Failed to parse Cursor error response', error);
-  }
-
-  return createAnthropicErrorResponse(response.status, type, message, headers);
-}
-
-async function createAnthropicJsonResponse(response: Response): Promise<Response> {
-  try {
-    const openAiResponse = await response.json();
-    if (!hasTranslatableChoices(openAiResponse)) {
-      return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
-    }
-
-    const anthropicResponse = new GlmtTransformer().transformResponse(openAiResponse);
-    if (isSyntheticTransformationFallback(anthropicResponse)) {
-      logTranslationError(
-        'Cursor JSON translation produced synthetic fallback response',
-        anthropicResponse
-      );
-      return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
-    }
-
-    return new Response(JSON.stringify(anthropicResponse), {
-      status: response.status,
-      headers: { 'Content-Type': 'application/json' },
-    });
-  } catch (error) {
-    logTranslationError('Cursor JSON translation failed', error);
-    return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
-  }
-}
-
-function createAnthropicStreamingResponse(response: Response): Response {
-  const body = response.body;
-  if (!body) {
-    return createAnthropicErrorResponse(
-      502,
-      'api_error',
-      'Cursor stream ended before a response body was available'
-    );
-  }
-
-  const parser = new SSEParser({ throwOnMalformedJson: true });
-  const transformer = new GlmtTransformer();
-  const accumulator = new DeltaAccumulator({});
-  const encoder = new TextEncoder();
-
-  const readable = new ReadableStream<Uint8Array>({
-    async start(controller) {
-      const reader = body.getReader();
-
-      try {
-        while (true) {
-          const { done, value } = await reader.read();
-          if (done) {
-            break;
-          }
-          if (!value) {
-            continue;
-          }
-
-          const events = parser.parse(Buffer.from(value));
-          events.forEach((event) => {
-            const anthropicEvents = transformer.transformDelta(event as SSEEvent, accumulator);
-            anthropicEvents.forEach((anthropicEvent) => {
-              controller.enqueue(
-                encoder.encode(formatSseEvent(anthropicEvent.event, anthropicEvent.data))
-              );
-            });
-          });
-        }
-
-        if (!accumulator.isFinalized() && accumulator.isMessageStarted()) {
-          transformer.finalizeDelta(accumulator).forEach((anthropicEvent) => {
-            controller.enqueue(
-              encoder.encode(formatSseEvent(anthropicEvent.event, anthropicEvent.data))
-            );
-          });
-        }
-      } catch (error) {
-        logTranslationError('Cursor SSE translation failed', error);
-        controller.enqueue(
-          encoder.encode(
-            formatSseEvent(
-              'error',
-              createAnthropicErrorPayload('api_error', STREAM_TRANSLATION_ERROR_MESSAGE)
-            )
-          )
-        );
-      } finally {
-        reader.releaseLock();
-        controller.close();
-      }
-    },
-  });
-
-  return new Response(readable, {
-    status: response.status,
-    headers: {
-      'Content-Type': 'text/event-stream',
-      'Cache-Control': 'no-cache',
-      Connection: 'keep-alive',
-    },
-  });
-}
-
-export async function createAnthropicProxyResponse(response: Response): Promise<Response> {
-  if (!response.ok) {
-    return createAnthropicErrorProxyResponse(response);
-  }
-
-  const contentType = (response.headers.get('content-type') || '').toLowerCase();
-  const isEventStream =
-    contentType === 'text/event-stream' || contentType.startsWith('text/event-stream;');
-
-  return isEventStream
-    ? createAnthropicStreamingResponse(response)
-    : createAnthropicJsonResponse(response);
-}
+export {
+  createAnthropicErrorResponse,
+  createAnthropicProxyResponse,
+} from '../proxy/transformers/sse-stream-transformer';

src/glmt/sse-parser.ts

@@ -49,7 +49,7 @@ export class SSEParser {
    * @returns Array of parsed events
    */
   parse(chunk: Buffer | string): SSEEvent[] {
-    this.buffer += chunk.toString().replace(/\r\n/g, '\n');
+    this.buffer += chunk.toString().replace(/\r\n?/g, '\n');
 
     // C-01 Fix: Prevent unbounded buffer growth (DoS protection)
     if (this.buffer.length > this.maxBufferSize) {

src/proxy/server/messages-route.ts

@@ -109,6 +109,61 @@ function formatTimeoutDuration(timeoutMs: number): string {
   return timeoutMs % 1000 === 0 ? `${timeoutMs / 1000} seconds` : `${timeoutMs}ms`;
 }
 
+function registerOnceListener(
+  emitter: NodeJS.EventEmitter | null | undefined,
+  event: string,
+  handler: () => void
+): () => void {
+  if (!emitter) {
+    return () => {};
+  }
+
+  emitter.once(event, handler);
+  return () => {
+    emitter.removeListener(event, handler);
+  };
+}
+
+export function attachDisconnectAbortHandlers(
+  req: http.IncomingMessage,
+  res: http.ServerResponse,
+  controller: AbortController,
+  onDisconnect: (source: string) => void
+): () => void {
+  const abortOnDisconnect = (source: string) => {
+    if (!controller.signal.aborted && !res.writableEnded) {
+      onDisconnect(source);
+      controller.abort();
+    }
+  };
+
+  const cleanupFns = [
+    registerOnceListener(req, 'aborted', () => abortOnDisconnect('req.aborted')),
+    registerOnceListener(req, 'close', () => abortOnDisconnect('req.close')),
+    registerOnceListener(req.socket, 'close', () => abortOnDisconnect('req.socket.close')),
+    registerOnceListener(res, 'close', () => abortOnDisconnect('res.close')),
+    registerOnceListener(res.socket, 'close', () => abortOnDisconnect('res.socket.close')),
+  ];
+
+  const disconnectPoll = setInterval(() => {
+    if (
+      req.destroyed ||
+      res.destroyed ||
+      req.socket?.destroyed === true ||
+      res.socket?.destroyed === true
+    ) {
+      abortOnDisconnect('poll.destroyed');
+    }
+  }, 50);
+
+  return () => {
+    clearInterval(disconnectPoll);
+    for (const cleanup of cleanupFns) {
+      cleanup();
+    }
+  };
+}
+
 export async function handleProxyMessagesRequest(
   req: http.IncomingMessage,
   res: http.ServerResponse,
@@ -145,8 +200,11 @@ export async function handleProxyMessagesRequest(
     const controller = new AbortController();
     timeoutMs = getRequestTimeoutMs();
     const timeout = setTimeout(() => controller.abort(), timeoutMs);
-    const abortOnDisconnect = (source: string) => {
-      if (!controller.signal.aborted && !res.writableEnded) {
+    const cleanupDisconnectHandlers = attachDisconnectAbortHandlers(
+      req,
+      res,
+      controller,
+      (source) => {
         logger.info(
           'request.disconnect',
           'Aborting upstream request after local client disconnect',
@@ -155,25 +213,8 @@ export async function handleProxyMessagesRequest(
             source,
           }
         );
-        controller.abort();
       }
-    };
-
-    req.on('aborted', () => abortOnDisconnect('req.aborted'));
-    req.on('close', () => abortOnDisconnect('req.close'));
-    req.socket?.on('close', () => abortOnDisconnect('req.socket.close'));
-    res.on('close', () => abortOnDisconnect('res.close'));
-    res.socket?.on('close', () => abortOnDisconnect('res.socket.close'));
-    const disconnectPoll = setInterval(() => {
-      if (
-        req.destroyed ||
-        res.destroyed ||
-        req.socket?.destroyed === true ||
-        res.socket?.destroyed === true
-      ) {
-        abortOnDisconnect('poll.destroyed');
-      }
-    }, 50);
+    );
 
     try {
       const upstreamResponse = await fetch(
@@ -181,7 +222,7 @@ export async function handleProxyMessagesRequest(
         buildFetchInit(upstream.route.profile, upstream.body, controller.signal, insecureDispatcher)
       );
       clearTimeout(timeout);
-      clearInterval(disconnectPoll);
+      cleanupDisconnectHandlers();
       logger.info('response.received', 'Received upstream response', {
         profileName: profile.profileName,
         routedProfileName: upstream.route.profile.profileName,
@@ -191,7 +232,7 @@ export async function handleProxyMessagesRequest(
       await pipeWebResponseToNode(response, res);
     } finally {
       clearTimeout(timeout);
-      clearInterval(disconnectPoll);
+      cleanupDisconnectHandlers();
     }
   } catch (error) {
     const message = error instanceof Error ? error.message : 'Unknown proxy error';

src/proxy/transformers/sse-stream-transformer.ts

@@ -1,7 +1,253 @@
-import {
-  createAnthropicErrorResponse,
-  createAnthropicProxyResponse,
-} from '../../cursor/cursor-anthropic-response';
+import { DeltaAccumulator } from '../../glmt/delta-accumulator';
+import { GlmtTransformer } from '../../glmt/glmt-transformer';
+import { SSEParser } from '../../glmt/sse-parser';
+import type { OpenAIResponse, SSEEvent } from '../../glmt/pipeline';
+
+const JSON_TRANSLATION_ERROR_MESSAGE = 'Failed to translate Cursor JSON response';
+const STREAM_TRANSLATION_ERROR_MESSAGE = 'Failed to translate Cursor SSE response';
+
+type ResponseHeaders = Headers | Record<string, string> | Array<[string, string]>;
+
+interface AnthropicErrorPayload {
+  type: 'error';
+  error: {
+    type: string;
+    message: string;
+  };
+}
+
+function createAnthropicErrorPayload(type: string, message: string): AnthropicErrorPayload {
+  return {
+    type: 'error',
+    error: {
+      type,
+      message,
+    },
+  };
+}
+
+function formatErrorForLog(error: unknown): string {
+  if (error instanceof Error) {
+    return error.message;
+  }
+
+  try {
+    return JSON.stringify(error);
+  } catch {
+    return String(error);
+  }
+}
+
+function logTranslationError(context: string, error: unknown): void {
+  console.error(`[proxy-sse-transformer] ${context}: ${formatErrorForLog(error)}`);
+}
+
+export function createAnthropicErrorResponse(
+  status: number,
+  type: string,
+  message: string,
+  headers?: ResponseHeaders
+): Response {
+  const responseHeaders = new Headers(headers);
+  responseHeaders.set('Content-Type', 'application/json');
+  responseHeaders.delete('Content-Length');
+
+  return new Response(JSON.stringify(createAnthropicErrorPayload(type, message)), {
+    status,
+    headers: responseHeaders,
+  });
+}
+
+function formatSseEvent(event: string, data: unknown): string {
+  return `event: ${event}\ndata: ${JSON.stringify(data)}\n\n`;
+}
+
+function hasTranslatableChoices(value: unknown): value is OpenAIResponse {
+  if (typeof value !== 'object' || value === null) {
+    return false;
+  }
+
+  const { choices } = value as OpenAIResponse;
+  if (!Array.isArray(choices) || choices.length === 0) {
+    return false;
+  }
+
+  const firstChoice = choices[0];
+  if (typeof firstChoice !== 'object' || firstChoice === null) {
+    return false;
+  }
+
+  const message = (firstChoice as { message?: unknown }).message;
+  return typeof message === 'object' && message !== null;
+}
+
+function isSyntheticTransformationFallback(value: unknown): boolean {
+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    typeof (value as { id?: unknown }).id === 'string' &&
+    (value as { id: string }).id.startsWith('msg_error_')
+  );
+}
+
+async function createAnthropicErrorProxyResponse(response: Response): Promise<Response> {
+  const headers = new Headers(response.headers);
+  headers.delete('Content-Type');
+  headers.delete('Content-Length');
+
+  let type =
+    response.status === 401
+      ? 'authentication_error'
+      : response.status === 429
+        ? 'rate_limit_error'
+        : response.status >= 400 && response.status < 500
+          ? 'invalid_request_error'
+          : 'api_error';
+  let message = `Cursor request failed with status ${response.status}`;
+
+  try {
+    const contentType = (response.headers.get('content-type') || '').toLowerCase();
+    if (contentType.includes('application/json')) {
+      const payload = (await response.json()) as {
+        error?: { type?: string; message?: string };
+        message?: string;
+      };
+
+      if (typeof payload?.error?.type === 'string' && payload.error.type.trim().length > 0) {
+        type = payload.error.type;
+      }
+
+      if (typeof payload?.error?.message === 'string' && payload.error.message.trim().length > 0) {
+        message = payload.error.message;
+      } else if (typeof payload?.message === 'string' && payload.message.trim().length > 0) {
+        message = payload.message;
+      }
+    } else {
+      const text = (await response.text()).trim();
+      if (text.length > 0) {
+        message = text;
+      }
+    }
+  } catch (error) {
+    logTranslationError('Failed to parse upstream error response', error);
+  }
+
+  return createAnthropicErrorResponse(response.status, type, message, headers);
+}
+
+async function createAnthropicJsonResponse(response: Response): Promise<Response> {
+  try {
+    const openAIResponse = await response.json();
+    if (!hasTranslatableChoices(openAIResponse)) {
+      return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
+    }
+
+    const anthropicResponse = new GlmtTransformer().transformResponse(openAIResponse);
+    if (isSyntheticTransformationFallback(anthropicResponse)) {
+      logTranslationError(
+        'Cursor JSON translation produced synthetic fallback response',
+        anthropicResponse
+      );
+      return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
+    }
+
+    return new Response(JSON.stringify(anthropicResponse), {
+      status: response.status,
+      headers: { 'Content-Type': 'application/json' },
+    });
+  } catch (error) {
+    logTranslationError('Cursor JSON translation failed', error);
+    return createAnthropicErrorResponse(502, 'api_error', JSON_TRANSLATION_ERROR_MESSAGE);
+  }
+}
+
+function createAnthropicStreamingResponse(response: Response): Response {
+  const body = response.body;
+  if (!body) {
+    return createAnthropicErrorResponse(
+      502,
+      'api_error',
+      'Cursor stream ended before a response body was available'
+    );
+  }
+
+  const parser = new SSEParser({ throwOnMalformedJson: true });
+  const transformer = new GlmtTransformer();
+  const accumulator = new DeltaAccumulator({});
+  const encoder = new TextEncoder();
+
+  const readable = new ReadableStream<Uint8Array>({
+    async start(controller) {
+      const reader = body.getReader();
+
+      try {
+        while (true) {
+          const { done, value } = await reader.read();
+          if (done) {
+            break;
+          }
+          if (!value) {
+            continue;
+          }
+
+          const events = parser.parse(Buffer.from(value));
+          for (const event of events) {
+            const anthropicEvents = transformer.transformDelta(event as SSEEvent, accumulator);
+            for (const anthropicEvent of anthropicEvents) {
+              controller.enqueue(
+                encoder.encode(formatSseEvent(anthropicEvent.event, anthropicEvent.data))
+              );
+            }
+          }
+        }
+
+        if (!accumulator.isFinalized() && accumulator.isMessageStarted()) {
+          for (const anthropicEvent of transformer.finalizeDelta(accumulator)) {
+            controller.enqueue(
+              encoder.encode(formatSseEvent(anthropicEvent.event, anthropicEvent.data))
+            );
+          }
+        }
+      } catch (error) {
+        logTranslationError('Cursor SSE translation failed', error);
+        controller.enqueue(
+          encoder.encode(
+            formatSseEvent(
+              'error',
+              createAnthropicErrorPayload('api_error', STREAM_TRANSLATION_ERROR_MESSAGE)
+            )
+          )
+        );
+      } finally {
+        reader.releaseLock();
+        controller.close();
+      }
+    },
+  });
+
+  return new Response(readable, {
+    status: response.status,
+    headers: {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+    },
+  });
+}
+
+export async function createAnthropicProxyResponse(response: Response): Promise<Response> {
+  if (!response.ok) {
+    return createAnthropicErrorProxyResponse(response);
+  }
+
+  const contentType = (response.headers.get('content-type') || '').toLowerCase();
+  const isEventStream =
+    contentType === 'text/event-stream' || contentType.startsWith('text/event-stream;');
+
+  return isEventStream
+    ? createAnthropicStreamingResponse(response)
+    : createAnthropicJsonResponse(response);
+}
 
 export class ProxySseStreamTransformer {
   async transform(response: Response): Promise<Response> {

tests/unit/glmt/sse-parser.test.ts

@@ -28,8 +28,22 @@ describe('SSEParser', () => {
     const events = parser.parse('\n\n');
 
     expect(events).toHaveLength(1);
-    expect((events[0]?.data as { choices?: Array<{ delta?: { content?: string } }> })?.choices?.[0]?.delta?.content).toBe(
-      'Hi'
+    expect(
+      (events[0]?.data as { choices?: Array<{ delta?: { content?: string } }> })?.choices?.[0]
+        ?.delta?.content
+    ).toBe('Hi');
+  });
+
+  it('accepts standalone carriage-return line endings', () => {
+    const parser = new SSEParser({ throwOnMalformedJson: true });
+    const events = parser.parse(
+      ['event: message', 'data: {"choices":[{"delta":{"content":"Legacy"}}]}', '', ''].join('\r')
     );
+
+    expect(events).toHaveLength(1);
+    expect(
+      (events[0]?.data as { choices?: Array<{ delta?: { content?: string } }> })?.choices?.[0]
+        ?.delta?.content
+    ).toBe('Legacy');
   });
 });

tests/unit/proxy/messages-route.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it } from 'bun:test';
+import { EventEmitter } from 'events';
+import { attachDisconnectAbortHandlers } from '../../../src/proxy/server/messages-route';
+
+class FakeSocket extends EventEmitter {
+  destroyed = false;
+}
+
+class FakeRequest extends EventEmitter {
+  destroyed = false;
+  socket = new FakeSocket();
+}
+
+class FakeResponse extends EventEmitter {
+  destroyed = false;
+  writableEnded = false;
+  socket = new FakeSocket();
+}
+
+describe('attachDisconnectAbortHandlers', () => {
+  it('cleans up registered listeners after the request completes', () => {
+    const req = new FakeRequest();
+    const res = new FakeResponse();
+    const controller = new AbortController();
+
+    const cleanup = attachDisconnectAbortHandlers(
+      req as never,
+      res as never,
+      controller,
+      () => {}
+    );
+
+    expect(req.listenerCount('aborted')).toBe(1);
+    expect(req.listenerCount('close')).toBe(1);
+    expect(req.socket.listenerCount('close')).toBe(1);
+    expect(res.listenerCount('close')).toBe(1);
+    expect(res.socket.listenerCount('close')).toBe(1);
+
+    cleanup();
+
+    expect(req.listenerCount('aborted')).toBe(0);
+    expect(req.listenerCount('close')).toBe(0);
+    expect(req.socket.listenerCount('close')).toBe(0);
+    expect(res.listenerCount('close')).toBe(0);
+    expect(res.socket.listenerCount('close')).toBe(0);
+  });
+
+  it('aborts at most once when disconnect signals race each other', () => {
+    const req = new FakeRequest();
+    const res = new FakeResponse();
+    const controller = new AbortController();
+    let disconnectCount = 0;
+
+    const cleanup = attachDisconnectAbortHandlers(
+      req as never,
+      res as never,
+      controller,
+      () => {
+        disconnectCount += 1;
+      }
+    );
+
+    req.emit('close');
+    req.socket.emit('close');
+    res.emit('close');
+
+    expect(controller.signal.aborted).toBe(true);
+    expect(disconnectCount).toBe(1);
+
+    cleanup();
+  });
+});

tests/unit/proxy/transformers/sse-stream-transformer.test.ts

@@ -0,0 +1,70 @@
+import { describe, expect, it } from 'bun:test';
+import { createAnthropicProxyResponse } from '../../../../src/proxy/transformers/sse-stream-transformer';
+
+describe('proxy SSE stream transformer', () => {
+  it('converts OpenAI JSON into Anthropic message JSON', async () => {
+    const response = new Response(
+      JSON.stringify({
+        id: 'chatcmpl_1',
+        model: 'claude-sonnet-4.5',
+        choices: [
+          {
+            index: 0,
+            message: {
+              role: 'assistant',
+              content: 'Here is the result.',
+              reasoning_content: 'Need to call the tool first.',
+              tool_calls: [
+                {
+                  id: 'toolu_2',
+                  type: 'function',
+                  function: { name: 'search', arguments: '{"q":"proxy"}' },
+                },
+              ],
+            },
+            finish_reason: 'tool_calls',
+          },
+        ],
+        usage: { prompt_tokens: 12, completion_tokens: 4, total_tokens: 16 },
+      }),
+      {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+      }
+    );
+
+    const transformed = await createAnthropicProxyResponse(response);
+    const body = (await transformed.json()) as {
+      type: string;
+      stop_reason: string;
+      content: Array<{ type: string; thinking?: string; name?: string }>;
+    };
+
+    expect(body.type).toBe('message');
+    expect(body.stop_reason).toBe('tool_use');
+    expect(body.content.map((block) => block.type)).toEqual(['thinking', 'text', 'tool_use']);
+    expect(body.content[0]?.thinking).toContain('Need to call the tool first');
+    expect(body.content[2]?.name).toBe('search');
+  });
+
+  it('converts OpenAI SSE chunks into Anthropic SSE events', async () => {
+    const openAISse = [
+      'data: {"id":"chatcmpl_2","object":"chat.completion.chunk","created":1,"model":"claude-sonnet-4.5","choices":[{"index":0,"delta":{"role":"assistant","content":"Hello"},"finish_reason":null}]}\n\n',
+      'data: {"id":"chatcmpl_2","object":"chat.completion.chunk","created":1,"model":"claude-sonnet-4.5","choices":[{"index":0,"delta":{},"finish_reason":"stop"}],"usage":{"prompt_tokens":5,"completion_tokens":1,"total_tokens":6}}\n\n',
+      'data: [DONE]\n\n',
+    ].join('');
+
+    const transformed = await createAnthropicProxyResponse(
+      new Response(openAISse, {
+        status: 200,
+        headers: { 'Content-Type': 'text/event-stream' },
+      })
+    );
+
+    const body = await transformed.text();
+    expect(body).toContain('event: message_start');
+    expect(body).toContain('event: content_block_start');
+    expect(body).toContain('"type":"text_delta"');
+    expect(body).toContain('event: message_stop');
+  });
+});