Always return message=success for completed executions

Non-zero exit codes are valid outcomes (e.g. code-verification workloads).
Setting error on non-zero exits caused validate_existing_response_file to
discard and re-run those responses on every resume.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: madiator

src/bespokelabs/curator/code_executor/code_execution_backend/sandbox_backend.py

@@ -91,21 +91,8 @@ def _execute_in_sandbox(
 
             files = _collect_sandbox_files(sb)
 
-            if result.exit_code == 0:
-                return CodeExecutionOutput(
-                    message="success",
-                    stdout=result.stdout,
-                    stderr=result.stderr,
-                    files=files,
-                )
-
-            error_message = f"Program exited with status code {result.exit_code}"
-            if result.stderr:
-                error_message = f"{error_message}\n\nError details:\n{result.stderr}"
-
             return CodeExecutionOutput(
-                message="error",
-                error=error_message,
+                message="success",
                 stdout=result.stdout,
                 stderr=result.stderr,
                 files=files,