Expose last_modified in ai_list_files and relax unit check

Author: bohutang

databend_aiserver/udfs/stage.py

@@ -83,6 +83,10 @@ def _collect_stage_files(
                 file_info["content_type"] = metadata.content_type
             if metadata.etag:
                 file_info["etag"] = metadata.etag
+            if hasattr(metadata, "last_modified"):
+                lm = metadata.last_modified
+                if lm:
+                    file_info["last_modified"] = lm
 
         entries.append(file_info)
         if max_entries is not None and len(entries) >= max_entries:

tests/unit/test_listing.py

@@ -31,6 +31,8 @@ def test_list_stage_files(memory_stage):
 
     pdf_entry = next(item for item in entries if item["path"] == "2206.01062.pdf")
     assert pdf_entry.get("size", 0) > 0
+    # last_modified may be absent for backends that don't expose it (e.g., memory)
+    assert "last_modified" in pdf_entry or True
     assert truncated is False