1. Replace let-else with if-let-Some to avoid compilation error
- let-else with return would return from the entire function
- if-let-Some correctly assigns to tool_registry and continues
2. Preserve original goal_objective_for_prompt behavior
- Return None (not fallback) when objective exists but goal is inactive
- Use state.is_active().then() to match original semantics
huqiantao
eb3a989eeb