Add Codex GPT 5.5 image support (#991)

tests/unit/image-generation.test.js

@@ -284,6 +284,57 @@ describe("handleImageGenerationCore", () => {
     expect(responseBody.data[0].b64_json).toBeTruthy();
   });
 
+  it("generates image with Codex gpt-5.5-image using current Codex version header", async () => {
+    global.fetch.mockResolvedValueOnce(
+      new Response(
+        [
+          "event: response.output_item.done",
+          'data: {"item":{"type":"image_generation_call","result":"base64codeximage"}}',
+          "",
+          "",
+        ].join("\n"),
+        { status: 200, headers: { "Content-Type": "text/event-stream" } }
+      )
+    );
+
+    const result = await handleImageGenerationCore({
+      body: {
+        prompt: "A green square",
+        size: "1024x1024",
+        output_format: "png",
+      },
+      modelInfo: { provider: "codex", model: "gpt-5.5-image" },
+      credentials: {
+        accessToken: "codex-token",
+        providerSpecificData: { chatgptAccountId: "account-123" },
+      },
+      log: null,
+    });
+
+    expect(result.success).toBe(true);
+    expect(global.fetch).toHaveBeenCalledWith(
+      "https://chatgpt.com/backend-api/codex/responses",
+      expect.objectContaining({
+        method: "POST",
+        headers: expect.objectContaining({
+          authorization: "Bearer codex-token",
+          "chatgpt-account-id": "account-123",
+          version: "0.129.0",
+        }),
+      })
+    );
+
+    const fetchCall = global.fetch.mock.calls[0];
+    const requestBody = JSON.parse(fetchCall[1].body);
+    expect(requestBody.model).toBe("gpt-5.5");
+    expect(requestBody.tools).toEqual([
+      { type: "image_generation", output_format: "png", size: "1024x1024" },
+    ]);
+
+    const responseBody = await result.response.json();
+    expect(responseBody.data[0].b64_json).toBe("base64codeximage");
+  });
+
   it("generates image with Cloudflare Workers AI JSON response", async () => {
     global.fetch.mockResolvedValueOnce(
       new Response(