fix(antigravity): preserve client identity on model catalog requests

Restrict the legacy IDE-version override to generation endpoints so
catalog and other passthrough requests keep their original User-Agent
and metadata.ideVersion, letting newer Antigravity releases see current
models like Gemini 3.7 Flash in the MITM selector.

Fixes #3414

src/mitm/antigravityIdeVersion.js

@@ -1,8 +1,8 @@
 "use strict";
 
-// Rewrite Antigravity IDE markers so upstream AG 2.x backend accepts the request.
-// User-Agent header (antigravity/<old>) and body.metadata.ideVersion are forced
-// to a known-good IDE version. Hardcoded MVP — toggle/version configurable later.
+// Rewrite Antigravity IDE markers on generation requests so upstream AG 2.x
+// backend accepts them. Catalog and other passthrough requests retain the
+// client's current identity. Hardcoded MVP — toggle/version configurable later.
 
 const ANTIGRAVITY_IDE_VERSION = "1.23.2";
 const ANTIGRAVITY_IDE_VERSION_OVERRIDE_ENABLED = true;
@@ -19,8 +19,10 @@ function rewriteAntigravityUserAgent(userAgent, version) {
   return userAgent.replace(/antigravity\/[^\s]+/, `antigravity/${version}`);
 }
 
-function applyAntigravityIdeVersionOverride(bodyBuffer, headers) {
-  if (!ANTIGRAVITY_IDE_VERSION_OVERRIDE_ENABLED) {
+function applyAntigravityIdeVersionOverride(bodyBuffer, headers, requestUrl) {
+  const isGenerationEndpoint = requestUrl?.includes(":generateContent") ||
+    requestUrl?.includes(":streamGenerateContent");
+  if (!ANTIGRAVITY_IDE_VERSION_OVERRIDE_ENABLED || !isGenerationEndpoint) {
     return { bodyBuffer, headers, applied: false, version: ANTIGRAVITY_IDE_VERSION };
   }
 

src/mitm/server.js

@@ -132,7 +132,7 @@ async function passthrough(req, res, bodyBuffer, onResponse) {
 
   const tool = getToolForHost(req.headers.host);
   const versionOverride = tool === "antigravity"
-    ? applyAntigravityIdeVersionOverride(bodyBuffer, req.headers)
+    ? applyAntigravityIdeVersionOverride(bodyBuffer, req.headers, req.url)
     : { bodyBuffer, headers: req.headers };
   const bodyForForwarding = versionOverride.bodyBuffer;
   const headersForForwarding = { ...versionOverride.headers, host: targetHost };

tests/unit/antigravity-ide-version.test.js

@@ -0,0 +1,89 @@
+import { createRequire } from "module";
+import { describe, expect, it } from "vitest";
+
+const require = createRequire(import.meta.url);
+const {
+  ANTIGRAVITY_IDE_VERSION,
+  applyAntigravityIdeVersionOverride,
+} = require("../../src/mitm/antigravityIdeVersion.js");
+
+const CURRENT_VERSION = "2.11.0";
+
+function makeRequest(metadata = { ideName: "antigravity", ideVersion: CURRENT_VERSION }) {
+  const bodyBuffer = Buffer.from(JSON.stringify({ metadata, request: { contents: [] } }));
+  const headers = {
+    "content-type": "application/json",
+    "content-length": String(bodyBuffer.length),
+    "user-agent": `antigravity/${CURRENT_VERSION}`,
+  };
+  return { bodyBuffer, headers };
+}
+
+describe("Antigravity IDE version override", () => {
+  it("preserves catalog request identity and bytes", () => {
+    const { bodyBuffer, headers } = makeRequest();
+
+    const result = applyAntigravityIdeVersionOverride(
+      bodyBuffer,
+      headers,
+      "/v1internal:fetchAvailableModels"
+    );
+
+    expect(result.applied).toBe(false);
+    expect(result.bodyBuffer).toBe(bodyBuffer);
+    expect(result.headers).toBe(headers);
+    expect(result.headers["user-agent"]).toBe(`antigravity/${CURRENT_VERSION}`);
+    expect(JSON.parse(result.bodyBuffer.toString()).metadata.ideVersion).toBe(CURRENT_VERSION);
+    expect(result.headers["content-length"]).toBe(String(bodyBuffer.length));
+  });
+
+  it.each([":generateContent", ":streamGenerateContent"])(
+    "rewrites identity for %s requests",
+    (endpoint) => {
+      const { bodyBuffer, headers } = makeRequest();
+
+      const result = applyAntigravityIdeVersionOverride(
+        bodyBuffer,
+        headers,
+        `/v1internal/models/gemini-3.7-flash-tiered${endpoint}`
+      );
+
+      expect(result.applied).toBe(true);
+      expect(result.bodyBuffer).not.toBe(bodyBuffer);
+      expect(result.headers["user-agent"]).toBe(`antigravity/${ANTIGRAVITY_IDE_VERSION}`);
+      expect(JSON.parse(result.bodyBuffer.toString()).metadata.ideVersion).toBe(ANTIGRAVITY_IDE_VERSION);
+    }
+  );
+
+  it("preserves malformed non-generation request content byte-for-byte", () => {
+    const bodyBuffer = Buffer.from([0xff, 0x00, 0x7b, 0x6e, 0x6f, 0x74, 0x2d, 0x6a, 0x73, 0x6f, 0x6e]);
+    const headers = {
+      "content-type": "application/octet-stream",
+      "content-length": String(bodyBuffer.length),
+      "user-agent": `antigravity/${CURRENT_VERSION}`,
+    };
+
+    const result = applyAntigravityIdeVersionOverride(bodyBuffer, headers, "/v1internal:loadCodeAssist");
+
+    expect(result.applied).toBe(false);
+    expect(result.bodyBuffer).toBe(bodyBuffer);
+    expect(result.headers).toBe(headers);
+  });
+
+  it("does not synthesize missing Antigravity identity", () => {
+    const bodyBuffer = Buffer.from(JSON.stringify({ metadata: {}, request: { contents: [] } }));
+    const headers = { "content-type": "application/json", "content-length": String(bodyBuffer.length) };
+
+    const result = applyAntigravityIdeVersionOverride(
+      bodyBuffer,
+      headers,
+      "/v1internal/models/gemini-3.7-flash-tiered:generateContent"
+    );
+
+    expect(result.applied).toBe(false);
+    expect(result.bodyBuffer).toBe(bodyBuffer);
+    expect(result.headers).toEqual(headers);
+    expect(result.headers).not.toHaveProperty("user-agent");
+    expect(JSON.parse(result.bodyBuffer.toString()).metadata).not.toHaveProperty("ideVersion");
+  });
+});