.Net: Python: Bug: AggregatorTerminationStrategy is not a TerminationStrategy and cannot be used with AgentGroupChat #14591

Describe the bug

AggregatorTerminationStrategy (python/semantic_kernel/agents/strategies/termination/aggregator_termination_strategy.py) cannot be used as a termination strategy for AgentGroupChat. It derives from KernelBaseModel instead of TerminationStrategy, and it exposes should_terminate_async instead of the should_terminate / should_agent_terminate methods that every other termination strategy has and that AgentGroupChat calls.

class AggregatorTerminationStrategy(KernelBaseModel):
    strategies: list[TerminationStrategy]
    condition: AggregateTerminationCondition = Field(default=AggregateTerminationCondition.ALL)

    async def should_terminate_async(self, agent, history) -> bool:
        ...

AgentGroupChat.termination_strategy is typed TerminationStrategy, so pydantic rejects the aggregator, and the class is exported from semantic_kernel.agents.strategies but has no way to be plugged in.

To Reproduce

Run against current main (5b4a326):

from semantic_kernel.agents import AgentGroupChat
from semantic_kernel.agents.strategies import AggregatorTerminationStrategy, DefaultTerminationStrategy

AgentGroupChat(
    termination_strategy=AggregatorTerminationStrategy(
        strategies=[DefaultTerminationStrategy(maximum_iterations=1)]
    )
)

Output:

pydantic_core._pydantic_core.ValidationError: 1 validation error for AgentGroupChat
termination_strategy
  Input should be a valid dictionary or instance of TerminationStrategy [type=model_type, input_value=AggregatorTerminationStra...onCondition.ALL: 'All'>), input_type=AggregatorTerminationStrategy]

The existing unit tests only call should_terminate_async directly, so they never exercise it through a group chat.

Expected behavior

AggregatorTerminationStrategy should be a TerminationStrategy (as in the .NET AggregatorTerminationStrategy), so it can be passed to AgentGroupChat, and it can be scoped with agents and limited with maximum_iterations like the other strategies.

Proposed fix

Make the class derive from TerminationStrategy and move the aggregation logic into should_agent_terminate. Keep should_terminate_async as a thin wrapper that calls it, so existing callers do not break.

I have a fix with tests ready and can open a PR.

Platform

• Language: Python
• Source: main branch (5b4a326)
• OS: Windows, Python 3.13