fix(antigravity): align provider fingerprint with IDE Desktop 2.1.1 (#2389)

Match captured official Antigravity IDE traffic: cloudcode-pa host,
antigravity/ide/2.1.1 User-Agent, IDE-shaped agent requestId, and drop
router-only stream/usage headers plus the legacy double system prompt.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/executors/antigravity.js

@@ -1,7 +1,7 @@
 import crypto from "crypto";
 import { BaseExecutor } from "./base.js";
 import { PROVIDERS } from "../config/providers.js";
-import { OAUTH_ENDPOINTS, ANTIGRAVITY_HEADERS, INTERNAL_REQUEST_HEADER, AG_DEFAULT_TOOLS, AG_TOOL_SUFFIX } from "../config/appConstants.js";
+import { OAUTH_ENDPOINTS, ANTIGRAVITY_HEADERS, AG_DEFAULT_TOOLS, AG_TOOL_SUFFIX } from "../config/appConstants.js";
 import { HTTP_STATUS } from "../config/runtimeConfig.js";
 import { resolveSessionId } from "../utils/sessionManager.js";
 import { proxyAwareFetch } from "../utils/proxyFetch.js";
@@ -18,7 +18,8 @@ function sanitizeFunctionName(name) {
 
 const MAX_RETRY_AFTER_MS = 10000;
 const ANTIGRAVITY_TRANSIENT_RETRY_MAX_MS = 15000;
-const MAX_ANTIGRAVITY_OUTPUT_TOKENS = 16384;
+const MAX_ANTIGRAVITY_OUTPUT_TOKENS = 64000;
+const ANTIGRAVITY_IDE_REQUEST_ID_RE = /^agent\/[^/]+\/\d+\/[^/]+\/\d+$/;
 
 const ANTIGRAVITY_TRANSIENT_ERROR_PATTERNS = [
   /high\s+traffic/i,
@@ -87,6 +88,27 @@ function parseImageConfig(model) {
   return config;
 }
 
+function uuidFromSeed(seed) {
+  const bytes = crypto.createHash("sha256").update(String(seed || "antigravity")).digest().subarray(0, 16);
+  bytes[6] = (bytes[6] & 0x0f) | 0x50;
+  bytes[8] = (bytes[8] & 0x3f) | 0x80;
+  const hex = bytes.toString("hex");
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`;
+}
+
+function buildIdeRequestId({ body, request, credentials, model, requestType }) {
+  if (ANTIGRAVITY_IDE_REQUEST_ID_RE.test(body?.requestId || "")) {
+    return body.requestId;
+  }
+
+  const sessionId = request?.sessionId || body?.request?.sessionId || credentials?._clientSessionId || credentials?.connectionId || credentials?.email || "anonymous";
+  const conversationId = uuidFromSeed(`antigravity:conversation:${sessionId}`);
+  const trajectoryId = uuidFromSeed(`antigravity:trajectory:${sessionId}:${model}:${requestType}`);
+  const contentCount = Array.isArray(request?.contents) ? request.contents.length : 1;
+  const step = Math.max(1, contentCount * 2 - 1);
+  return `agent/${conversationId}/${Date.now()}/${trajectoryId}/${step}`;
+}
+
 export class AntigravityExecutor extends BaseExecutor {
   constructor() {
     super("antigravity", PROVIDERS.antigravity);
@@ -104,14 +126,10 @@ export class AntigravityExecutor extends BaseExecutor {
   // sessionId comes from transformRequest output; base.execute runs transformRequest before
   // buildHeaders, so we read it from instance state cached there (fallback: explicit arg).
   buildHeaders(credentials, stream = true, sessionId = null) {
-    const sid = sessionId || this._lastSessionId;
     return {
       "Content-Type": "application/json",
       "Authorization": `Bearer ${credentials.accessToken}`,
       "User-Agent": this.config.headers?.["User-Agent"] || ANTIGRAVITY_HEADERS["User-Agent"],
-      [INTERNAL_REQUEST_HEADER.name]: INTERNAL_REQUEST_HEADER.value,
-      ...(sid && { "X-Machine-Session-Id": sid }),
-      "Accept": stream ? "text/event-stream" : "application/json"
     };
   }
 
@@ -142,25 +160,26 @@ export class AntigravityExecutor extends BaseExecutor {
       });
 
       this._lastSessionId = sessionId;
+      const request = {
+        contents,
+        generationConfig: {
+          temperature: 1.0,
+          topP: 0.95,
+          topK: 40,
+          maxOutputTokens: 8192,
+          imageConfig,
+        },
+        sessionId,
+        // No tools, no systemInstruction, no safetySettings for image gen
+      };
 
       return {
         project: projectId,
         model: cleanModel,
         userAgent: "antigravity",
         requestType: "image_gen",
-        requestId: `agent-${crypto.randomUUID()}`,
-        request: {
-          contents,
-          generationConfig: {
-            temperature: 1.0,
-            topP: 0.95,
-            topK: 40,
-            maxOutputTokens: 8192,
-            imageConfig,
-          },
-          sessionId,
-          // No tools, no systemInstruction, no safetySettings for image gen
-        },
+        requestId: buildIdeRequestId({ body, request, credentials, model: cleanModel, requestType: "image_gen" }),
+        request,
       };
     }
 
@@ -248,7 +267,7 @@ export class AntigravityExecutor extends BaseExecutor {
       model: model,
       userAgent: "antigravity",
       requestType: "agent",
-      requestId: `agent-${crypto.randomUUID()}`,
+      requestId: buildIdeRequestId({ body, request: transformedRequest, credentials, model, requestType: "agent" }),
       request: transformedRequest
     };
   }