Require data URLs for code-mode image output (#33659)

## What changed

- Accept image output from `image()` and `generatedImage()` only when its URL
  uses the `data:` scheme.
- Preserve the dedicated error for remote HTTP URLs and report other malformed
  or unsupported image URLs as invalid image output.

## Testing

- Add service-level coverage for rejecting invalid output from both image
  helpers.
- Add an end-to-end code-mode test that verifies the tool call fails instead of
  returning an invalid image item.

GitOrigin-RevId: beaf8c8830574150e8166b6ff5daf7f6dc4dc0a1

codex-rs/core/tests/suite/code_mode.rs

@@ -2983,6 +2983,49 @@ async fn code_mode_image_helper_rejects_remote_url() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn code_mode_image_helper_rejects_invalid_image_output() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let (_test, second_mock) = run_code_mode_turn(
+        &server,
+        "use exec to return an image",
+        r#"
+const s = "Error executing tool exec: Expected at least one message to convert to CallToolResult";
+image(s.trim(), "original");
+"#,
+    )
+    .await?;
+
+    let req = second_mock.single_request();
+    let items = custom_tool_output_items(&req, "call-1");
+    let (_, success) = custom_tool_output_body_and_success(&req, "call-1");
+    assert_ne!(
+        success,
+        Some(true),
+        "code_mode invalid image output unexpectedly succeeded"
+    );
+    assert_eq!(items.len(), 2);
+    assert_regex_match(
+        concat!(
+            r"(?s)\A",
+            r"Script failed\nWall time \d+\.\d seconds\nOutput:\n\z"
+        ),
+        text_item(&items, /*index*/ 0),
+    );
+    assert_eq!(
+        text_item(&items, /*index*/ 1),
+        concat!(
+            "Script error:\n",
+            "Tool call failed: invalid image output. ",
+            "Pass a base64 data URI instead"
+        )
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn code_mode_can_use_view_image_result_with_image_helper() -> Result<()> {
     skip_if_no_network!(Ok(()));