Enhance comparison agent with reasoning loop and explicit stop condition

[Abirate]

Summary

This update improves the comparison_root_agent structure within
python/agents/brand-search-optimization/brand_search_optimization/sub_agents/comparison/agent.py.

The enhancement introduces a clear reasoning loop (via LoopAgent) that iterates between the
generator and critic sub-agents until the critic is satisfied, using an explicit stop tool.

Key Changes

• Added LoopAgent named comparison_review_loop to manage iterative reasoning.
• Introduced a stop_comparison tool to terminate the loop once the critic approves.
• Updated comparison_root_agent to wrap the loop for clearer orchestration.
• Maintains backward compatibility with existing multi-agent architecture.

Benefits

• Leverages the built-in LoopAgent structure in ADK to manage iterative reasoning between agents safely and declaratively.
• Prevents uncontrolled or infinite reasoning loops by providing an explicit stop condition (stop_comparison tool).
• Makes the comparison refinement process more transparent and logically structured.
• Simplifies extension and debugging by encapsulating generator–critic interactions within a single, controlled loop.
• Improves overall maintainability, readability, and reasoning traceability in ADK multi-agent workflows.

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