diff --git a/backend/app/gateway/routers/artifacts.py b/backend/app/gateway/routers/artifacts.py
index 78ea5fa000..9cd5d1f2f6 100644
--- a/backend/app/gateway/routers/artifacts.py
+++ b/backend/app/gateway/routers/artifacts.py
@@ -175,9 +175,15 @@ async def get_artifact(thread_id: str, path: str, request: Request, download: bo
         return FileResponse(path=actual_path, filename=actual_path.name, media_type=mime_type, headers=_build_attachment_headers(actual_path.name))
 
     if mime_type and mime_type.startswith("text/"):
-        return PlainTextResponse(content=actual_path.read_text(encoding="utf-8"), media_type=mime_type)
+        try:
+            return PlainTextResponse(content=actual_path.read_text(encoding="utf-8"), media_type=mime_type)
+        except UnicodeDecodeError:
+            pass  # Fall through to binary response
 
     if is_text_file_by_content(actual_path):
-        return PlainTextResponse(content=actual_path.read_text(encoding="utf-8"), media_type=mime_type)
+        try:
+            return PlainTextResponse(content=actual_path.read_text(encoding="utf-8"), media_type=mime_type)
+        except UnicodeDecodeError:
+            pass  # Fall through to binary response
 
     return Response(content=actual_path.read_bytes(), media_type=mime_type, headers={"Content-Disposition": _build_content_disposition("inline", actual_path.name)})
diff --git a/backend/packages/harness/deerflow/sandbox/tools.py b/backend/packages/harness/deerflow/sandbox/tools.py
index 32ee7d6468..3451f282d1 100644
--- a/backend/packages/harness/deerflow/sandbox/tools.py
+++ b/backend/packages/harness/deerflow/sandbox/tools.py
@@ -1569,6 +1569,9 @@ def str_replace_tool(
             if replace_all:
                 content = content.replace(old_str, new_str)
             else:
+                count = content.count(old_str)
+                if count > 1:
+                    return f"Error: The string to replace appears {count} times in {requested_path}. Use replace_all=True to replace all occurrences, or provide a more specific string that appears exactly once."
                 content = content.replace(old_str, new_str, 1)
             sandbox.write_file(path, content)
         return "OK"