Function calculateRegret

Learning exports - Closed-loop feedback and routing improvement Split from index.ts for file size compliance (Issue #285)

calculateRegret(
    decisions: readonly {
        chosenModel: string;
        actualReward: number;
        rewards: Record<string, number>;
    }[],
): RegretAnalysis
Calculate regret analysis comparing actual decisions vs oracle (best possible).
Parameters
- decisions: readonly {
      chosenModel: string;
      actualReward: number;
      rewards: Record<string, number>;
  }[]
Returns RegretAnalysis
- Defined in packages/nexus-agents/src/learning/validation-stats.ts:214