fix(cursor): harden anthropic daemon contract handling

src/cursor/cursor-anthropic-response.ts

@@ -5,23 +5,59 @@ 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]>;
 
-function createErrorResponse(message: string): Response {
+interface AnthropicErrorPayload {
-  return new Response(
+  type: 'error';
-    JSON.stringify({
+  error: {
-      error: {
+    type: string;
-        type: 'api_error',
+    message: string;
-        message,
+  };
-      },
-    }),
-    {
-      status: 502,
-      headers: { 'Content-Type': 'application/json' },
-    }
-  );
 }
 
-function formatSseEvent(event: string, data: Record<string, unknown>): 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`;
 }
 
@@ -31,33 +67,110 @@ function hasTranslatableChoices(value: unknown): value is OpenAIResponse {
   }
 
   const { choices } = value as OpenAIResponse;
-  return Array.isArray(choices) && choices.length > 0;
+  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 createErrorResponse(JSON_TRANSLATION_ERROR_MESSAGE);
+      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 {
+  } catch (error) {
-    return createErrorResponse(JSON_TRANSLATION_ERROR_MESSAGE);
+    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 createErrorResponse('Cursor stream ended before a response body was available');
+    return createAnthropicErrorResponse(
+      502,
+      'api_error',
+      'Cursor stream ended before a response body was available'
+    );
   }
 
-  const parser = new SSEParser();
+  const parser = new SSEParser({ throwOnMalformedJson: true });
   const transformer = new GlmtTransformer();
   const accumulator = new DeltaAccumulator({});
   const encoder = new TextEncoder();
@@ -94,16 +207,14 @@ function createAnthropicStreamingResponse(response: Response): Response {
             );
           });
         }
-      } catch {
+      } catch (error) {
+        logTranslationError('Cursor SSE translation failed', error);
         controller.enqueue(
           encoder.encode(
-            formatSseEvent('error', {
+            formatSseEvent(
-              type: 'error',
+              'error',
-              error: {
+              createAnthropicErrorPayload('api_error', STREAM_TRANSLATION_ERROR_MESSAGE)
-                type: 'api_error',
+            )
-                message: STREAM_TRANSLATION_ERROR_MESSAGE,
-              },
-            })
           )
         );
       } finally {
@@ -125,11 +236,14 @@ function createAnthropicStreamingResponse(response: Response): Response {
 
 export async function createAnthropicProxyResponse(response: Response): Promise<Response> {
   if (!response.ok) {
-    return response;
+    return createAnthropicErrorProxyResponse(response);
   }
 
-  const contentType = response.headers.get('content-type') || '';
+  const contentType = (response.headers.get('content-type') || '').toLowerCase();
-  return contentType.includes('text/event-stream')
+  const isEventStream =
+    contentType === 'text/event-stream' || contentType.startsWith('text/event-stream;');
+
+  return isEventStream
     ? createAnthropicStreamingResponse(response)
     : createAnthropicJsonResponse(response);
 }

src/cursor/cursor-anthropic-translator.ts

@@ -157,10 +157,22 @@ export function translateAnthropicRequest(raw: unknown): TranslatedAnthropicRequ
             `messages[${messageIndex}].content[${blockIndex}] tool_result requires user role`
           );
         }
+        if (typeof parsed.tool_use_id !== 'string' || parsed.tool_use_id.trim().length === 0) {
+          throw new Error(
+            `messages[${messageIndex}].content[${blockIndex}].tool_use_id must be a non-empty string`
+          );
+        }
         sawToolResult = true;
+        if (textParts.length > 0) {
+          translatedMessages.push({
+            role,
+            content: textParts.join('\n'),
+          });
+          textParts.length = 0;
+        }
         translatedMessages.push({
           role: 'tool',
-          tool_call_id: typeof parsed.tool_use_id === 'string' ? parsed.tool_use_id : '',
+          tool_call_id: parsed.tool_use_id,
           content: toToolResultContent(
             parsed.content,
             `messages[${messageIndex}].content[${blockIndex}].content`

src/cursor/cursor-daemon-entry.ts

@@ -7,7 +7,10 @@
 import * as http from 'http';
 import { Readable } from 'stream';
 import { CursorExecutor } from './cursor-executor';
-import { createAnthropicProxyResponse } from './cursor-anthropic-response';
+import {
+  createAnthropicErrorResponse,
+  createAnthropicProxyResponse,
+} from './cursor-anthropic-response';
 import { translateAnthropicRequest } from './cursor-anthropic-translator';
 import { checkAuthStatus } from './cursor-auth';
 import { getModelsForDaemon, resolveCursorRequestModel } from './cursor-models';
@@ -192,10 +195,12 @@ export function startCursorDaemonServer(options: DaemonRuntimeOptions): http.Ser
   const executor = new CursorExecutor();
 
   const server = http.createServer(async (req, res) => {
-    try {
+    const method = req.method || 'GET';
-      const method = req.method || 'GET';
+    const requestUrl = req.url || '/';
-      const requestUrl = req.url || '/';
+    const isOpenAiRoute = method === 'POST' && requestUrl === '/v1/chat/completions';
+    const isAnthropicRoute = method === 'POST' && requestUrl === '/v1/messages';
 
+    try {
       if (method === 'GET' && requestUrl === '/health') {
         writeJson(res, 200, { ok: true, service: 'cursor-daemon' });
         return;
@@ -224,9 +229,6 @@ export function startCursorDaemonServer(options: DaemonRuntimeOptions): http.Ser
         return;
       }
 
-      const isOpenAiRoute = method === 'POST' && requestUrl === '/v1/chat/completions';
-      const isAnthropicRoute = method === 'POST' && requestUrl === '/v1/messages';
-
       if (!isOpenAiRoute && !isAnthropicRoute) {
         writeJson(res, 404, { error: 'Not found' });
         return;
@@ -246,22 +248,38 @@ export function startCursorDaemonServer(options: DaemonRuntimeOptions): http.Ser
 
       const authStatus = checkAuthStatus();
       if (!authStatus.authenticated || !authStatus.credentials) {
-        writeJson(res, 401, {
+        const message = 'Cursor credentials not found. Run `ccs cursor auth` first.';
-          error: {
+        if (isAnthropicRoute) {
-            type: 'authentication_error',
+          await pipeWebResponseToNode(
-            message: 'Cursor credentials not found. Run `ccs cursor auth` first.',
+            createAnthropicErrorResponse(401, 'authentication_error', message),
-          },
+            res
-        });
+          );
+        } else {
+          writeJson(res, 401, {
+            error: {
+              type: 'authentication_error',
+              message,
+            },
+          });
+        }
         return;
       }
 
       if (authStatus.expired) {
-        writeJson(res, 401, {
+        const message = 'Cursor credentials expired. Run `ccs cursor auth` again.';
-          error: {
+        if (isAnthropicRoute) {
-            type: 'authentication_error',
+          await pipeWebResponseToNode(
-            message: 'Cursor credentials expired. Run `ccs cursor auth` again.',
+            createAnthropicErrorResponse(401, 'authentication_error', message),
-          },
+            res
-        });
+          );
+        } else {
+          writeJson(res, 401, {
+            error: {
+              type: 'authentication_error',
+              message,
+            },
+          });
+        }
         return;
       }
 
@@ -318,12 +336,20 @@ export function startCursorDaemonServer(options: DaemonRuntimeOptions): http.Ser
     } catch (error) {
       const message = error instanceof Error ? error.message : 'Unknown error';
       const isPayloadTooLarge = message.includes('Request body too large');
-      writeJson(res, isPayloadTooLarge ? 413 : 400, {
+      const status = isPayloadTooLarge ? 413 : 400;
-        error: {
+      if (isAnthropicRoute) {
-          type: 'invalid_request_error',
+        await pipeWebResponseToNode(
-          message,
+          createAnthropicErrorResponse(status, 'invalid_request_error', message),
-        },
+          res
-      });
+        );
+      } else {
+        writeJson(res, status, {
+          error: {
+            type: 'invalid_request_error',
+            message,
+          },
+        });
+      }
     }
   });
 

src/cursor/cursor-models.ts

@@ -281,6 +281,48 @@ function getCatalogDefaultModelId(availableModels: CursorModel[]): string {
   return firstAvailable || DEFAULT_CURSOR_MODEL;
 }
 
+function addLookupCandidate(candidates: Set<string>, value: string): void {
+  const normalized = value.trim().toLowerCase();
+  if (normalized) {
+    candidates.add(normalized);
+  }
+}
+
+function buildCursorAnthropicModelLookupCandidates(requestedModel: string): string[] {
+  const candidates = new Set<string>();
+  const raw = requestedModel.trim().toLowerCase();
+  addLookupCandidate(candidates, raw);
+
+  let normalized = raw.replace(/^[a-z0-9_-]+\//, '');
+  addLookupCandidate(candidates, normalized);
+
+  while (true) {
+    const stripped = normalized
+      .replace(/\(\d+\)$/i, '')
+      .replace(/\[1m\]$/i, '')
+      .replace(/-thinking$/i, '')
+      .replace(/-\d{8}$/i, '');
+
+    if (stripped === normalized) {
+      break;
+    }
+
+    normalized = stripped;
+    addLookupCandidate(candidates, normalized);
+  }
+
+  const anthropicAliasMatch = normalized.match(
+    /^claude-(opus|sonnet|haiku)-(\d+)(?:[.-](\d+))?(?:-(1m|fast-mode))?$/i
+  );
+  if (anthropicAliasMatch) {
+    const [, family, major, minor, variant] = anthropicAliasMatch;
+    const cursorModelId = `claude-${major}${minor ? `.${minor}` : ''}-${family.toLowerCase()}${variant ? `-${variant.toLowerCase()}` : ''}`;
+    addLookupCandidate(candidates, cursorModelId);
+  }
+
+  return [...candidates];
+}
+
 export function resolveCursorRequestModel(
   requestedModel: string | null | undefined,
   availableModels: CursorModel[]
@@ -291,8 +333,12 @@ export function resolveCursorRequestModel(
     return fallbackModel;
   }
 
-  if (availableModels.some((model) => model.id === normalizedRequested)) {
+  const lookupCandidates = new Set(buildCursorAnthropicModelLookupCandidates(normalizedRequested));
-    return normalizedRequested;
+  const matchedModel = availableModels.find((model) =>
+    lookupCandidates.has(model.id.toLowerCase())
+  );
+  if (matchedModel) {
+    return matchedModel.id;
   }
 
   return fallbackModel;

src/glmt/sse-parser.ts

@@ -19,6 +19,7 @@
 
 interface SSEParserOptions {
   maxBufferSize?: number;
+  throwOnMalformedJson?: boolean;
 }
 
 interface SSEEvent {
@@ -33,11 +34,13 @@ export class SSEParser {
   private buffer: string;
   private eventCount: number;
   private maxBufferSize: number;
+  private throwOnMalformedJson: boolean;
 
   constructor(options: SSEParserOptions = {}) {
     this.buffer = '';
     this.eventCount = 0;
     this.maxBufferSize = options.maxBufferSize || 1024 * 1024; // 1MB default
+    this.throwOnMalformedJson = options.throwOnMalformedJson === true;
   }
 
   /**
@@ -92,6 +95,9 @@ export class SSEParser {
                 data.substring(0, 100)
               );
             }
+            if (this.throwOnMalformedJson) {
+              throw new Error(`Malformed SSE JSON event: ${(e as Error).message}`);
+            }
           }
         }
       } else if (line.startsWith('id: ')) {

tests/integration/cursor-daemon-lifecycle.test.ts

@@ -68,6 +68,13 @@ describe('cursor daemon lifecycle smoke', () => {
       }),
     });
     expect(anthropicResponse.status).toBe(401);
+    const anthropicBody = (await anthropicResponse.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(anthropicBody.type).toBe('error');
+    expect(anthropicBody.error?.type).toBe('authentication_error');
+    expect(anthropicBody.error?.message).toContain('Run `ccs cursor auth` first');
 
     const stopResult = await stopDaemon();
     expect(stopResult.success).toBe(true);
@@ -146,6 +153,13 @@ describe('cursor daemon lifecycle smoke', () => {
       }),
     });
     expect(invalidAnthropic.status).toBe(400);
+    const invalidAnthropicBody = (await invalidAnthropic.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(invalidAnthropicBody.type).toBe('error');
+    expect(invalidAnthropicBody.error?.type).toBe('invalid_request_error');
+    expect(invalidAnthropicBody.error?.message).toContain('is not supported');
 
     const oversized = await fetch(`http://127.0.0.1:${port}/v1/chat/completions`, {
       method: 'POST',

tests/unit/cursor/cursor-anthropic-translator.test.ts

@@ -90,6 +90,27 @@ describe('translateAnthropicRequest', () => {
     ]);
   });
 
+  it('preserves mixed user text around tool_result blocks in order', () => {
+    const translated = translateAnthropicRequest({
+      messages: [
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: 'before' },
+            { type: 'tool_result', tool_use_id: 'toolu_1', content: 'done' },
+            { type: 'text', text: 'after' },
+          ],
+        },
+      ],
+    });
+
+    expect(translated.messages).toEqual([
+      { role: 'user', content: 'before' },
+      { role: 'tool', tool_call_id: 'toolu_1', content: 'done' },
+      { role: 'user', content: 'after' },
+    ]);
+  });
+
   it('handles empty messages arrays', () => {
     const translated = translateAnthropicRequest({ messages: [] });
 
@@ -150,6 +171,19 @@ describe('translateAnthropicRequest', () => {
     ]);
   });
 
+  it('rejects tool_result blocks without a non-empty tool_use_id', () => {
+    expect(() =>
+      translateAnthropicRequest({
+        messages: [
+          {
+            role: 'user',
+            content: [{ type: 'tool_result', tool_use_id: '   ', content: 'done' }],
+          },
+        ],
+      })
+    ).toThrow('tool_use_id must be a non-empty string');
+  });
+
   it('falls back when tool_use input cannot be serialized', () => {
     const circular: Record<string, unknown> = {};
     circular.self = circular;
@@ -241,7 +275,11 @@ describe('createAnthropicProxyResponse', () => {
     );
 
     expect(transformed.status).toBe(502);
-    const body = (await transformed.json()) as { error?: { type?: string; message?: string } };
+    const body = (await transformed.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(body.type).toBe('error');
     expect(body.error?.type).toBe('api_error');
     expect(body.error?.message).toBe('Failed to translate Cursor JSON response');
   });
@@ -261,7 +299,11 @@ describe('createAnthropicProxyResponse', () => {
     );
 
     expect(transformed.status).toBe(502);
-    const body = (await transformed.json()) as { error?: { type?: string; message?: string } };
+    const body = (await transformed.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(body.type).toBe('error');
     expect(body.error?.type).toBe('api_error');
     expect(body.error?.message).toBe('Failed to translate Cursor JSON response');
   });
@@ -282,7 +324,63 @@ describe('createAnthropicProxyResponse', () => {
     );
 
     expect(transformed.status).toBe(502);
-    const body = (await transformed.json()) as { error?: { type?: string; message?: string } };
+    const body = (await transformed.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(body.type).toBe('error');
+    expect(body.error?.type).toBe('api_error');
+    expect(body.error?.message).toBe('Failed to translate Cursor JSON response');
+  });
+
+  it('returns Anthropic error envelopes for non-OK upstream JSON errors', async () => {
+    const transformed = await createAnthropicProxyResponse(
+      new Response(
+        JSON.stringify({
+          error: {
+            type: 'invalid_request_error',
+            message: '[400]: upstream rejected request',
+          },
+        }),
+        {
+          status: 400,
+          headers: { 'Content-Type': 'application/json', 'Retry-After': '7' },
+        }
+      )
+    );
+
+    expect(transformed.status).toBe(400);
+    expect(transformed.headers.get('retry-after')).toBe('7');
+    const body = (await transformed.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(body.type).toBe('error');
+    expect(body.error?.type).toBe('invalid_request_error');
+    expect(body.error?.message).toBe('[400]: upstream rejected request');
+  });
+
+  it('returns 502 when Cursor response choices are malformed', async () => {
+    const transformed = await createAnthropicProxyResponse(
+      new Response(
+        JSON.stringify({
+          id: 'chatcmpl_missing_message',
+          model: 'claude-sonnet-4.5',
+          choices: [{ index: 0 }],
+        }),
+        {
+          status: 200,
+          headers: { 'Content-Type': 'application/json' },
+        }
+      )
+    );
+
+    expect(transformed.status).toBe(502);
+    const body = (await transformed.json()) as {
+      type?: string;
+      error?: { type?: string; message?: string };
+    };
+    expect(body.type).toBe('error');
     expect(body.error?.type).toBe('api_error');
     expect(body.error?.message).toBe('Failed to translate Cursor JSON response');
   });
@@ -324,4 +422,19 @@ describe('createAnthropicProxyResponse', () => {
     expect(body).toContain('"error":{"type":"api_error"');
     expect(body).toContain('Failed to translate Cursor SSE response');
   });
+
+  it('emits Anthropic-style error events when SSE JSON is malformed', async () => {
+    const transformed = await createAnthropicProxyResponse(
+      new Response('data: {not-json}\n\n', {
+        status: 200,
+        headers: { 'Content-Type': 'text/event-stream; charset=utf-8' },
+      })
+    );
+
+    const body = await transformed.text();
+    expect(body).toContain('event: error');
+    expect(body).toContain('"type":"error"');
+    expect(body).toContain('"error":{"type":"api_error"');
+    expect(body).toContain('Failed to translate Cursor SSE response');
+  });
 });

tests/unit/cursor/cursor-models.test.ts

@@ -57,6 +57,19 @@ describe('resolveCursorRequestModel', () => {
     expect(resolved).toBe('claude-4.6-opus');
   });
 
+  it('maps Anthropic family-first aliases to the matching Cursor model id', () => {
+    const resolved = resolveCursorRequestModel('claude-sonnet-4.5', DEFAULT_CURSOR_MODELS);
+    expect(resolved).toBe('claude-4.5-sonnet');
+  });
+
+  it('strips provider, dated, and thinking suffixes before resolving Anthropic aliases', () => {
+    const resolved = resolveCursorRequestModel(
+      'anthropic/claude-sonnet-4.5-20250929-thinking',
+      DEFAULT_CURSOR_MODELS
+    );
+    expect(resolved).toBe('claude-4.5-sonnet');
+  });
+
   it('falls back to default when requested model is unavailable', () => {
     const resolved = resolveCursorRequestModel('non-existent-model', DEFAULT_CURSOR_MODELS);
     expect(resolved).toBe(DEFAULT_CURSOR_MODEL);