[Backend] loanCheckCron re-sends the same repayment due notification every hour

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

src/cron/loanCheckCron.ts runs hourly and for every unrepaid loan older than 30 days creates a fresh repayment_due notification (lines 28-36) with no dedup, no already-notified check and no idempotency, so an affected borrower is spammed 24 times a day indefinitely.

Acceptance criteria

• Only notify when a borrower has not already been notified for that loan within a window (track last-notified or use a unique guard)
• Replace the hardcoded 30-day heuristic with the actual loan due date / term where available
• Add a distributed lock so multiple instances do not duplicate (coordinate with the scheduler-lock issue)
• Add a test asserting a single notification per due loan per cycle window

Files to touch

• src/cron/loanCheckCron.ts
• src/services/notificationService.ts

Out of scope

• Building a full repayment-schedule table
• Email/SMS template redesign

[MarvyNwaokobia]

I'd like to work on this issue.

I have experience with backend cron jobs, notification systems, and idempotency patterns. I'll update the loan check cron to prevent duplicate notifications by adding a per-loan notification guard (last-notified or unique key), and ensure borrowers are only notified once per defined cycle window.

I'll also replace the hardcoded 30-day logic with the actual loan due date or term where available, add a distributed lock to prevent duplicate runs across instances, and update the notification service accordingly. Finally, I'll add a test to verify only one notification is sent per loan per cycle window.

[grantfox-oss]

🦊 GrantFox — @MarvyNwaokobia has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #10)
2. Your PR will be reviewed by the LabsCrypt maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@MarvyNwaokobia's PR #38 was approved and merged by @ogazboiz.

🏆 @MarvyNwaokobia: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (156 total points). Track your full progress on GrantFox.

👏 Great work, @MarvyNwaokobia! Keep contributing to LabsCrypt.