fix(antigravity): strip stream_options from non-stream requests

OpenAI clients may send stream_options with stream=false; Google
generateContent rejects that combination. Drop it when not streaming.

open-sse/executors/antigravity.js

@@ -136,6 +136,10 @@ export class AntigravityExecutor extends BaseExecutor {
   transformRequest(model, body, stream, credentials) {
     const projectId = credentials?.projectId || this.generateProjectId();
 
+    // OpenAI clients may include stream_options even for non-streaming calls.
+    // Google generateContent rejects that combination before processing the request.
+    if (stream !== true) delete body.stream_options;
+
     // ─── Image generation: completely different request structure ───
     if (isImageModel(model)) {
       const imageConfig = parseImageConfig(model);

tests/unit/antigravity-stream-options.test.js

@@ -0,0 +1,45 @@
+import { describe, expect, it } from "vitest";
+import { AntigravityExecutor } from "../../open-sse/executors/antigravity.js";
+
+const credentials = {
+  projectId: "synthetic-project",
+  connectionId: "synthetic-connection",
+};
+
+function requestBody(stream) {
+  return {
+    stream,
+    stream_options: { include_usage: true },
+    request: {
+      contents: [{ role: "user", parts: [{ text: "Reply only OK" }] }],
+    },
+  };
+}
+
+describe("AntigravityExecutor stream_options normalization", () => {
+  it("removes stream_options from a non-streaming request", () => {
+    const executor = new AntigravityExecutor();
+    const output = executor.transformRequest(
+      "gpt-oss-120b-medium",
+      requestBody(false),
+      false,
+      credentials,
+    );
+
+    expect(output.stream).toBe(false);
+    expect(output.stream_options).toBeUndefined();
+  });
+
+  it("preserves stream_options for a streaming request", () => {
+    const executor = new AntigravityExecutor();
+    const output = executor.transformRequest(
+      "gpt-oss-120b-medium",
+      requestBody(true),
+      true,
+      credentials,
+    );
+
+    expect(output.stream).toBe(true);
+    expect(output.stream_options).toEqual({ include_usage: true });
+  });
+});