This pull request includes several changes to the browser_use package, focusing on refactoring the MessageManager class and updating the SystemPrompt class to load prompt templates from a markdown file. Additionally, there are updates to the test cases to align with the refactored code.

Refactoring and improvements:

• browser_use/agent/message_manager/service.py: Removed unnecessary page summary from the current_state dictionary in _init_messages and added error handling for trailing newlines and extracting only the last line of the error in add_state_message. [1] [2]

• browser_use/agent/prompts.py: Refactored SystemPrompt to load prompt templates from a markdown file using importlib.resources and removed hardcoded rules and input format methods. [1] [2]

Updates to test cases:

• browser_use/agent/message_manager/tests.py: Updated test cases to use the new MessageManagerSettings and SystemMessage instead of SystemPrompt, and adjusted assertions to match the refactored MessageManager class structure. [1] [2] [3] [4] [5] [6] [7]

• browser_use/agent/tests.py: Removed page summaries from AgentHistory instances in the sample_history function and updated a debug print statement. [1] [2] [3] [4]

New markdown file for prompt templates:

• browser_use/agent/system_prompt.md: Added a new markdown file containing the prompt template for the SystemPrompt class.