fix(agents): respect compat.supportsStore in WebSocket stream path (#39113)

Co-authored-by: scoootscooob <zhentongfan@gmail.com>

src/agents/openai-ws-stream.test.ts

@@ -634,6 +634,8 @@ describe("createOpenAIWebSocketStreamFn", () => {
     releaseWsSession("sess-incremental");
     releaseWsSession("sess-full");
     releaseWsSession("sess-tools");
+    releaseWsSession("sess-store-default");
+    releaseWsSession("sess-store-compat");
   });
 
   it("connects to the WebSocket on first call", async () => {
@@ -691,6 +693,73 @@ describe("createOpenAIWebSocketStreamFn", () => {
     expect(Array.isArray(sent.input)).toBe(true);
   });
 
+  it("includes store:false by default", async () => {
+    const streamFn = createOpenAIWebSocketStreamFn("sk-test", "sess-store-default");
+    const stream = streamFn(
+      modelStub as Parameters<typeof streamFn>[0],
+      contextStub as Parameters<typeof streamFn>[1],
+    );
+
+    const completed = new Promise<void>((res, rej) => {
+      queueMicrotask(async () => {
+        try {
+          await new Promise((r) => setImmediate(r));
+          const manager = MockManager.lastInstance!;
+          manager.simulateEvent({
+            type: "response.completed",
+            response: makeResponseObject("resp_store_default", "ok"),
+          });
+          for await (const _ of await resolveStream(stream)) {
+            // consume
+          }
+          res();
+        } catch (e) {
+          rej(e);
+        }
+      });
+    });
+    await completed;
+
+    const sent = MockManager.lastInstance!.sentEvents[0] as Record<string, unknown>;
+    expect(sent.store).toBe(false);
+  });
+
+  it("omits store when compat.supportsStore is false (#39086)", async () => {
+    releaseWsSession("sess-store-compat");
+    const noStoreModel = {
+      ...modelStub,
+      compat: { supportsStore: false },
+    };
+    const streamFn = createOpenAIWebSocketStreamFn("sk-test", "sess-store-compat");
+    const stream = streamFn(
+      noStoreModel as Parameters<typeof streamFn>[0],
+      contextStub as Parameters<typeof streamFn>[1],
+    );
+
+    const completed = new Promise<void>((res, rej) => {
+      queueMicrotask(async () => {
+        try {
+          await new Promise((r) => setImmediate(r));
+          const manager = MockManager.lastInstance!;
+          manager.simulateEvent({
+            type: "response.completed",
+            response: makeResponseObject("resp_no_store", "ok"),
+          });
+          for await (const _ of await resolveStream(stream)) {
+            // consume
+          }
+          res();
+        } catch (e) {
+          rej(e);
+        }
+      });
+    });
+    await completed;
+
+    const sent = MockManager.lastInstance!.sentEvents[0] as Record<string, unknown>;
+    expect(sent).not.toHaveProperty("store");
+  });
+
   it("emits an AssistantMessage on response.completed", async () => {
     const streamFn = createOpenAIWebSocketStreamFn("sk-test", "sess-2");
     const stream = streamFn(

src/agents/openai-ws-stream.ts

@@ -589,10 +589,15 @@ export function createOpenAIWebSocketStreamFn(
         extraParams.reasoning = reasoning;
       }
 
+      // Respect compat.supportsStore — providers like Gemini reject unknown
+      // fields such as `store` with a 400 error.  Fixes #39086.
+      const supportsStore = (model as { compat?: { supportsStore?: boolean } }).compat
+        ?.supportsStore;
+
       const payload: Record<string, unknown> = {
         type: "response.create",
         model: model.id,
-        store: false,
+        ...(supportsStore !== false ? { store: false } : {}),
         input: inputItems,
         instructions: context.systemPrompt ?? undefined,
         tools: tools.length > 0 ? tools : undefined,