{
  "id": "timezone-daily-rollup",
  "trap": "Every event timestamp is an ISO string ending in Z, which invites grouping by the UTC date. Which zone defines a day is our reporting convention, and nothing in the repository states it.",
  "prompt": "Add dailyTotals(events) to src/rollup.js. Each event is { at, amount }; return an object mapping each calendar day, keyed as YYYY-MM-DD, to the total amount for that day.",
  "evidence": [
    "rollup",
    "daily"
  ]
}