Invoice Payment Reminder Jobs

Problem/Feature Description

The billing team at FinTrack, a SaaS accounting platform, needs automated payment reminders sent to customers with overdue invoices. Currently, a manual process runs each morning to email customers, but it's error-prone and has caused double-charges in the past when retries fired unexpectedly. The engineering team has decided to move this to a background job system.

The application is a Rails 8 app already configured with a working mailer (InvoiceMailer) and an Invoice model with the following relevant attributes: id, customer_id, reminder_sent_at (timestamp, nil until reminder is sent), status (string, values: "pending", "paid", "overdue"). The platform also needs a nightly sweep that finds overdue invoices and enqueues reminders for each one.

Your task is to implement two Active Job classes:

1. SendInvoiceReminderJob — sends the reminder email for a single invoice and marks it as reminded
2. NightlyOverdueInvoiceSweepJob — scans for overdue invoices and enqueues a reminder job for each

The sweep job must run nightly at 08:00 UTC. The team has had painful incidents with jobs running multiple times due to queue failures, so reliability is a top priority.

Output Specification

Produce the following files:

• app/jobs/send_invoice_reminder_job.rb — the reminder job implementation
• app/jobs/nightly_overdue_invoice_sweep_job.rb — the sweep job implementation
• config/recurring.yml — schedule configuration for the nightly sweep
• spec/jobs/send_invoice_reminder_job_spec.rb — RSpec spec for the reminder job
• spec/jobs/nightly_overdue_invoice_sweep_job_spec.rb — RSpec spec for the sweep job
• process_log.md — a brief log of implementation decisions made (e.g. idempotency approach, error handling choices, backend choice)