async def on_activity_request(self, core_activity: CoreActivity, request: Request, response: Response) -> Any:
        """Handle incoming Teams activity."""
        # Get validated token from middleware (if present - will be missing if skip_auth is True)
        if hasattr(request.state, "validated_token") and request.state.validated_token:
            token = request.state.validated_token
        else:
            token = cast(
                TokenProtocol,
                SimpleNamespace(
                    app_id="",
                    app_display_name="",
                    tenant_id="",
                    service_url=core_activity.service_url or "",
                    from_="azure",
                    from_id="",
                    is_expired=lambda: False,
                ),
            )

        activity_type = core_activity.type or "unknown"
        activity_id = core_activity.id or "unknown"

        self.logger.debug(f"Received activity: {activity_type} (ID: {activity_id})")
        self.logger.debug(f"Processing activity {activity_id} via handler...")

        # Process the activity
        result = await self._process_activity(core_activity, token)
        return self._handle_activity_response(response, result)

    def _setup_routes(self) -> None:
        """Setup FastAPI routes."""

        self.app.post("/api/messages")(self.on_activity_request)