Layered configuration — the unified config tree, agent config, and the XML/empathy config layer

Notes & tips

• Prefer the unified tree for new code. UnifiedConfig + load_unified_config + validate_config is the modern path.
• AttuneConfig ≡ EmpathyConfig. Same class, two names.
• load_config and load_unified_config differ. Different return types; pick one and stay consistent.
• Use set_config() for the XML config. It swaps the global instance other code reads.