Reset a failed tool call (#5666)

Co-authored-by: openhands <openhands@all-hands.dev>

openhands/controller/agent_controller.py

@@ -335,6 +335,28 @@ class AgentController:
     def _reset(self) -> None:
         """Resets the agent controller"""
 
+        # make sure there is an Observation with the tool call metadata to be recognized by the agent
+        # otherwise the pending action is found in history, but it's incomplete without an obs with tool result
+        if self._pending_action and hasattr(self._pending_action, 'tool_call_metadata'):
+            # find out if there already is an observation with the same tool call metadata
+            found_observation = False
+            for event in self.state.history:
+                if (
+                    isinstance(event, Observation)
+                    and event.tool_call_metadata
+                    == self._pending_action.tool_call_metadata
+                ):
+                    found_observation = True
+                    break
+
+            # make a new ErrorObservation with the tool call metadata
+            if not found_observation:
+                obs = ErrorObservation(content='The action has not been executed.')
+                obs.tool_call_metadata = self._pending_action.tool_call_metadata
+                obs._cause = self._pending_action.id  # type: ignore[attr-defined]
+                self.event_stream.add_event(obs, EventSource.AGENT)
+
+        # reset the pending action, this will be called when the agent is STOPPED or ERROR
         self._pending_action = None
         self.agent.reset()