Notifications App
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**Purpose**: Centralized communication engine for SMS, email, WhatsApp messages, and call logging across all workflows.

Responsibilities
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- Send notifications via multiple channels: SMS, email, WhatsApp, push
- Manage notification templates with dynamic placeholders
- Log all phone calls (introductory, confirmation, post-install, emergency)
- Track delivery status (queued → sent → delivered / failed)
- Provide notification history per user

Dependencies
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- **accounts** — Recipient user, caller user

Key Models
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- **Notification** — A message sent to a user via a specific channel. Includes context (which lead/survey/installation triggered it) and delivery tracking.
- **NotificationTemplate** — Reusable message templates with Django template syntax for dynamic content (customer name, survey date, etc.).
- **CallLog** — Records every phone call made in the system: who called, purpose, outcome (connected, no answer, busy), duration, and notes.
- **DeliveryReceipt** — Webhook-driven delivery confirmation from SMS/WhatsApp gateways.

Business Rules
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- Every status change that affects a customer should trigger a notification.
- Call logs are mandatory for: introductory calls, survey day confirmation, installation day confirmation, post-installation confirmation.
- Templates are channel-specific — an SMS template differs from an email template for the same event.
- Failed notifications are retried up to 3 times with exponential backoff.
- Notification preferences are not user-configurable in v1 — all notifications are sent per workflow rules.