feat: add images support to the Codex Typescript SDK (#5281)

Extend `run` and `runStreamed` input to be either a `string` or
structured input. A structured input is an array of text parts and/or
image paths, which will then be fed to the CLI through the `--image`
argument. Text parts are combined with double newlines. For instance:

```ts
const turn = await thread.run([
  { type: "text", text: "Describe these screenshots" },
  { type: "local_image", path: "./ui.png" },
  { type: "local_image", path: "./diagram.jpg" },
  { type: "text", text: "Thanks!" },
]);
```

Ends up launching the CLI with:

```
codex exec --image foo.png --image bar.png "Describe these screenshots\n\nThanks!" 
```

The complete `Input` type for both function now is:

```ts
export type UserInput =
  | {
      type: "text";
      text: string;
    }
  | {
      type: "local_image";
      path: string;
    };

export type Input = string | UserInput[];
```

This brings the Codex SDK closer to feature parity with the CLI.
Adresses #5280 .

sdk/typescript/tests/run.test.ts

@@ -279,6 +279,82 @@ describe("Codex", () => {
       await close();
     }
   });
+  it("combines structured text input segments", async () => {
+    const { url, close, requests } = await startResponsesTestProxy({
+      statusCode: 200,
+      responseBodies: [
+        sse(
+          responseStarted("response_1"),
+          assistantMessage("Combined input applied", "item_1"),
+          responseCompleted("response_1"),
+        ),
+      ],
+    });
+
+    try {
+      const client = new Codex({ codexPathOverride: codexExecPath, baseUrl: url, apiKey: "test" });
+
+      const thread = client.startThread();
+      await thread.run([
+        { type: "text", text: "Describe file changes" },
+        { type: "text", text: "Focus on impacted tests" },
+      ]);
+
+      const payload = requests[0];
+      expect(payload).toBeDefined();
+      const lastUser = payload!.json.input.at(-1);
+      expect(lastUser?.content?.[0]?.text).toBe("Describe file changes\n\nFocus on impacted tests");
+    } finally {
+      await close();
+    }
+  });
+  it("forwards images to exec", async () => {
+    const { url, close } = await startResponsesTestProxy({
+      statusCode: 200,
+      responseBodies: [
+        sse(
+          responseStarted("response_1"),
+          assistantMessage("Images applied", "item_1"),
+          responseCompleted("response_1"),
+        ),
+      ],
+    });
+
+    const { args: spawnArgs, restore } = codexExecSpy();
+    const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "codex-images-"));
+    const imagesDirectoryEntries: [string, string] = [
+      path.join(tempDir, "first.png"),
+      path.join(tempDir, "second.jpg"),
+    ];
+    imagesDirectoryEntries.forEach((image, index) => {
+      fs.writeFileSync(image, `image-${index}`);
+    });
+
+    try {
+      const client = new Codex({ codexPathOverride: codexExecPath, baseUrl: url, apiKey: "test" });
+
+      const thread = client.startThread();
+      await thread.run([
+        { type: "text", text: "describe the images" },
+        { type: "local_image", path: imagesDirectoryEntries[0] },
+        { type: "local_image", path: imagesDirectoryEntries[1] },
+      ]);
+
+      const commandArgs = spawnArgs[0];
+      expect(commandArgs).toBeDefined();
+      const forwardedImages: string[] = [];
+      for (let i = 0; i < commandArgs!.length; i += 1) {
+        if (commandArgs![i] === "--image") {
+          forwardedImages.push(commandArgs![i + 1] ?? "");
+        }
+      }
+      expect(forwardedImages).toEqual(imagesDirectoryEntries);
+    } finally {
+      fs.rmSync(tempDir, { recursive: true, force: true });
+      restore();
+      await close();
+    }
+  });
   it("runs in provided working directory", async () => {
     const { url, close } = await startResponsesTestProxy({
       statusCode: 200,