Explain: add revert-on-failure behaviour to ugo_sender

If switching to the sending process fails, restore the debugger to its
original position so the failed tool call does not leave the session in
an unexpected state.

Author: barisione

explain/explain.py

@@ -453,6 +453,7 @@ def _call_handler(_):
     @report
     @source_context
     @collect_output
+    @revert_time_on_failure
     @chain_of_thought
     def tool_ugo_sender(self) -> None:
         """