feat: add session tracking and cleanup for AgentCoreBrowser

Implement proper session lifecycle management for browser instances:

Code changes:
- Add _client_dict to track active browser sessions by session_id
- Populate _client_dict in create_browser_session() for session tracking
- Register atexit handler in __init__() to ensure cleanup on process exit
- Ensures browser sessions are properly closed when process terminates

Tests:
- test_bedrock_browser_create_browser_session_hydrates_client_dict:
  Verifies _client_dict is populated when sessions are created

- test_bedrock_browser_registers_atexit_handler:
  Confirms cleanup handler is registered at initialization

This prevents resource leaks from orphaned browser sessions and ensures
all active sessions are tracked and cleaned up properly.

Author: bennorwood

src/strands_tools/browser/agent_core_browser.py

@@ -5,6 +5,7 @@
 AWS-hosted browser instances.
 """
 
+import atexit
 import logging
 from typing import Dict, Optional
 
@@ -36,6 +37,7 @@ def __init__(self, region: Optional[str] = None, identifier: Optional[str] = Non
         self.identifier = identifier or "aws.browser.v1"
         self.session_timeout = session_timeout
         self._client_dict: Dict[str, AgentCoreBrowserClient] = {}
+        atexit.register(super().close_platform)
 
     def start_platform(self) -> None:
         """Remote platform does not need additional initialization steps."""
@@ -49,6 +51,7 @@ async def create_browser_session(self) -> PlaywrightBrowser:
         # Create new browser client for this session
         session_client = AgentCoreBrowserClient(region=self.region)
         session_id = session_client.start(identifier=self.identifier, session_timeout_seconds=self.session_timeout)
+        self._client_dict[session_id] = session_client
 
         logger.info(f"started Bedrock AgentCore browser session: {session_id}")
 

tests/browser/test_agent_core_browser.py

@@ -2,7 +2,7 @@
 Unit tests for the AgentCoreBrowser implementation.
 """
 
-from unittest.mock import Mock
+from unittest.mock import Mock, patch
 
 import pytest
 
@@ -17,6 +17,21 @@ def test_bedrock_browser_initialization():
     assert browser._client_dict == {}
 
 
+def test_bedrock_browser_registers_atexit_handler():
+    """Test that close_platform is registered with atexit on initialization."""
+
+    with patch("strands_tools.browser.agent_core_browser.atexit.register") as mock_atexit:
+        AgentCoreBrowser()
+        
+        # Verify atexit.register was called once
+        mock_atexit.assert_called_once()
+        
+        # Verify it registered the parent class's close_platform method
+        # (atexit.register is called with super().close_platform)
+        registered_func = mock_atexit.call_args[0][0]
+        assert callable(registered_func)
+
+
 def test_bedrock_browser_with_custom_params():
     """Test AgentCoreBrowser initialization with custom parameters."""
     browser = AgentCoreBrowser(region="us-east-1", session_timeout=7200)
@@ -58,6 +73,40 @@ async def test_bedrock_browser_create_browser_session_no_playwright():
         await browser.create_browser_session()
 
 
+@pytest.mark.asyncio
+async def test_bedrock_browser_create_browser_session_hydrates_client_dict():
+    """Test that _client_dict is hydrated when create_browser_session is called."""
+    from unittest.mock import AsyncMock, patch
+
+    browser = AgentCoreBrowser()
+    
+    # Mock playwright
+    mock_playwright = Mock()
+    mock_chromium = Mock()
+    mock_browser = Mock()
+    mock_playwright.chromium = mock_chromium
+    mock_chromium.connect_over_cdp = AsyncMock(return_value=mock_browser)
+    browser._playwright = mock_playwright
+    
+    # Mock BrowserClient
+    mock_client = Mock()
+    mock_session_id = "test-session-123"
+    mock_client.start.return_value = mock_session_id
+    mock_client.generate_ws_headers.return_value = ("ws://test-url", {"header": "value"})
+    
+    with patch("strands_tools.browser.agent_core_browser.AgentCoreBrowserClient", return_value=mock_client):
+        # Verify _client_dict is empty before
+        assert browser._client_dict == {}
+        
+        # Create browser session
+        await browser.create_browser_session()
+        
+        # Verify _client_dict is hydrated with the session
+        assert mock_session_id in browser._client_dict
+        assert browser._client_dict[mock_session_id] == mock_client
+        assert len(browser._client_dict) == 1
+
+
 def test_bedrock_browser_start_platform():
     """Test AgentCoreBrowser browser start platform (should be no-op)."""
     browser = AgentCoreBrowser()