# Economy Module

- All currency values are `bigint`. Never use `Number()` for arithmetic on balances -- use BigInt literals (e.g., `0n`, `500n`) and `sql` template expressions for DB updates.
- `modifyUserBalance` is the canonical way to change a user's balance. It checks for insufficient funds on negative amounts, logs a transaction record, and emits `BALANCE_CHANGED` for quest progression. Bypass it only if you have a very good reason.
- Daily rewards reset at **UTC midnight**, not 24h from last claim. The cooldown `expiresAt` is set to the next UTC 00:00:00. Streak breaks if the user misses an entire 24h window after the cooldown expired.
- Daily reward is capped at `MAX_DAILY_REWARD = 500n` regardless of streak/weekly bonus.
- The streak has a grace period: if a user's timer record is missing (e.g., DB migration), the code allows one "free" increment to avoid unfair resets.
- Weekly bonus triggers every 7th consecutive day (streak % 7 === 0).
- **Exam system**: a weekly check-in that rewards users based on XP gained since their last exam. The reward uses scaled BigInt arithmetic (`* 10000 / 10000n`) to avoid floating-point precision loss. Exams are locked to a specific day of the week set at registration time. Missing your exam day means zero reward -- there is no retroactive claim.
- Lootdrops use **in-memory state** (`Map`s for channel activity and cooldowns). This state is lost on restart. The DB stores only spawned/claimed drops. Claiming uses an atomic `UPDATE ... WHERE claimedBy IS NULL` to prevent race conditions.
- Lootdrops expire after 10 minutes and are cleaned up by a 60-second interval.
