store state message in the history (#3271)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Store the state message text in the agent history so clients can see the
exact state prompt used for each step and debug more easily.

- New Features
  - Save last_state_message_text when creating state messages.
- Pass state_message into history items via _finalize and
_make_history_item.
  - Extend AgentHistory and model_dump to include state_message.

<!-- End of auto-generated description by cubic. -->

browser_use/agent/message_manager/service.py

@@ -129,6 +129,7 @@ class MessageManager:
 		self.include_attributes = include_attributes or []
 		self.sensitive_data = sensitive_data
 		self.last_input_messages = []
+		self.last_state_message_text: str | None = None
 		# Only initialize messages if state is empty
 		if len(self.state.history.get_messages()) == 0:
 			self._set_message_with_type(self.system_prompt, 'system')
@@ -355,6 +356,9 @@ class MessageManager:
 			sample_images=self.sample_images,
 		).get_user_message(effective_use_vision)
 
+		# Store state message text for history
+		self.last_state_message_text = state_message.text
+
 		# Set the state message with caching enabled
 		self._set_message_with_type(state_message, 'state')
 

browser_use/agent/service.py

@@ -850,7 +850,13 @@ class Agent(Generic[Context, AgentStructuredOutput]):
 			)
 
 			# Use _make_history_item like main branch
-			await self._make_history_item(self.state.last_model_output, browser_state_summary, self.state.last_result, metadata)
+			await self._make_history_item(
+				self.state.last_model_output,
+				browser_state_summary,
+				self.state.last_result,
+				metadata,
+				state_message=self._message_manager.last_state_message_text,
+			)
 
 		# Log step completion summary
 		self._log_step_completion_summary(self.step_start_time, self.state.last_result)
@@ -980,6 +986,7 @@ class Agent(Generic[Context, AgentStructuredOutput]):
 		browser_state_summary: BrowserStateSummary,
 		result: list[ActionResult],
 		metadata: StepMetadata | None = None,
+		state_message: str | None = None,
 	) -> None:
 		"""Create and store history item"""
 
@@ -1012,6 +1019,7 @@ class Agent(Generic[Context, AgentStructuredOutput]):
 			result=result,
 			state=state_history,
 			metadata=metadata,
+			state_message=state_message,
 		)
 
 		self.history.add_item(history_item)

browser_use/agent/views.py

@@ -249,6 +249,7 @@ class AgentHistory(BaseModel):
 	result: list[ActionResult]
 	state: BrowserStateHistory
 	metadata: StepMetadata | None = None
+	state_message: str | None = None
 
 	model_config = ConfigDict(arbitrary_types_allowed=True, protected_namespaces=())
 
@@ -353,6 +354,7 @@ class AgentHistory(BaseModel):
 			'result': result_dump,
 			'state': self.state.to_dict(),
 			'metadata': self.metadata.model_dump() if self.metadata else None,
+			'state_message': self.state_message,
 		}