Fix #6227 - Add MessageStore abstraction for external message persistence in all 5 team types

[Whning0513]

Add MessageStore base class abstraction for storing message thread in teams

Feature request from maintainer ekzhu: Add a simple storage abstraction for message_thread with a TTL policy parameter. This enables teams to persist their message history externally (e.g., to databases or other storage backends) rather than keeping it only in memory.

Filed by: ekzhu (maintainer)

Teams stored message history solely in memory within BaseGroupChatManager. There was no abstraction layer to support external persistence, which limited scalability and recovery capabilities for long-running conversations.

11 files changed, primarily:

File 1: python/packages/autogen-agentchat/src/autogen_agentchat/storage/_message_store.py (new)

• Created MessageStore base class with TTL policy support
• Defines the interface for storing and retrieving message threads

File 2: python/packages/autogen-agentchat/src/autogen_agentchat/storage/__init__.py

• Exported the new MessageStore class

Files 3-11: Team implementations

• Updated _base_group_chat.py, _base_group_chat_manager.py, _events.py
• Updated all 5 team types: RoundRobinGroupChat (_round_robin_group_chat.py), SelectorGroupChat (_selector_group_chat.py), SwarmGroupChat (_swarm_group_chat.py), MagenticOneGroupChat (_magentic_one_group_chat.py, _magentic_one_orchestrator.py), DiGraphGroupChat (_digraph_group_chat.py)
• Each team accepts an optional message_store parameter and uses it for message persistence

Low - The new MessageStore abstraction is entirely opt-in through an optional constructor parameter. Teams that do not provide a message_store continue to use the default in-memory behavior with no changes. New storage implementations can be added without modifying team code.

[Whning0513]

@microsoft-github-policy-service agree