Return the full-resolution image URL from image_search (#3990)

`image_search` set both `image_url` and `thumbnail_url` to the DDGS result's
`thumbnail` field, so the tool never returned the full-resolution image even
though its docstring/usage_hint promise reference-quality images (and a result
with no `thumbnail` returned an empty `image_url`). DDGS `.images()` exposes the
full-res source under the separate `image` key — read that for `image_url`,
matching the serper/brave providers which keep image vs thumbnail distinct.

Adds a regression test.

backend/packages/harness/deerflow/community/image_search/tools.py

@@ -119,7 +119,7 @@ def image_search_tool(
     normalized_results = [
         {
             "title": r.get("title", ""),
-            "image_url": r.get("thumbnail", ""),
+            "image_url": r.get("image", ""),
             "thumbnail_url": r.get("thumbnail", ""),
         }
         for r in results

backend/tests/test_image_search.py

@@ -0,0 +1,28 @@
+import json
+from unittest.mock import MagicMock, patch
+
+from deerflow.community.image_search.tools import image_search_tool
+
+
+def test_image_search_uses_full_image_url_not_thumbnail():
+    # Regression: `image_url` must expose the full-resolution `image` from the DDGS result,
+    # not the low-res `thumbnail` (both fields were previously set to `thumbnail`).
+    fake_results = [
+        {
+            "title": "a cat",
+            "image": "https://example.com/full.jpg",
+            "thumbnail": "https://example.com/thumb.jpg",
+        }
+    ]
+    cfg = MagicMock()
+    cfg.get_tool_config.return_value = None
+
+    with (
+        patch("deerflow.community.image_search.tools._search_images", return_value=fake_results),
+        patch("deerflow.community.image_search.tools.get_app_config", return_value=cfg),
+    ):
+        output = json.loads(image_search_tool.invoke({"query": "a cat"}))
+
+    result = output["results"][0]
+    assert result["image_url"] == "https://example.com/full.jpg"
+    assert result["thumbnail_url"] == "https://example.com/thumb.jpg"