Function mergeRewards

mergeRewards(
    existing: Record<string, TiltifyReward[]>,
    incoming: Record<string, TiltifyReward[]> | undefined,
    authoritative?: boolean,
): Record<string, TiltifyReward[]>
Accumulates rewards across ticks, keyed by campaign ID then reward ID.
Parameters
- existing: Record<string, TiltifyReward[]>
  Current per-campaign reward map.
- incoming: Record<string, TiltifyReward[]> | undefined
  Fresh per-campaign reward map (may be undefined).
- authoritative: boolean = false
  When true, replace the named campaigns wholesale instead of merging. Defaults to false.
Returns Record<string, TiltifyReward[]>
Merged map with rewards preserved across ticks.
- Defined in realtime-pipeline/src/reducer/tiltifyData.ts:141