This pull request includes several changes to improve the initialization and state management of the browser context and agent services. The changes focus on better handling of message initialization, callback registration, and browser context state management, including the use of CDP (Chrome DevTools Protocol) for more precise control over browser tabs and pages.

Improvements to message initialization:

• browser_use/agent/message_manager/service.py: Added _init_messages method to initialize message history only if the state history is empty.

Enhancements to callback registration:

• browser_use/agent/service.py: Replaced register_external_agent_status_callback with register_external_agent_status_raise_error_callback and updated related methods to handle asynchronous checks for agent status. [1] [2] [3] [4] [5] [6] [7] [8]

Browser context state management improvements:

• browser_use/browser/context.py: Introduced BrowserContextState to manage the state of the browser context, including handling of CDP target IDs for more precise tab and page control. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Minor improvements:

• browser_use/agent/views.py: Updated the description for the action field in AgentOutput and its custom model creation method. [1] [2]
• browser_use/controller/service.py: Modified element click action to use get_selector_map and get_dom_element_by_index for better element handling.