> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vritti.works/llms.txt
> Use this file to discover all available pages before exploring further.

# Offline Queue & Sync Engine

> How Vritti Lens operates during network outages with UUID idempotency.

# Offline Queue & Synchronization Engine

Vritti Lens is engineered to function continuously during internet connectivity drops or power disruptions.

## Architecture

When an employee scans their face at a Vritti Lens kiosk:

1. **Local Vector Comparison**: Face embeddings are processed locally on-device without calling an external API.
2. **Local SQLite Event Queue**: Successful identifications generate an `AttendanceEvent` record assigned a unique UUIDv4 key, stored in the tablet's local SQLite database.
3. **Audio-Visual Feedback**: The kiosk plays a confirmation audio tone ("Attendance Marked for \[Staff Name]") immediately.

## Automatic Sync Behavior

* Vritti Lens runs a background sync worker that monitors network status.
* Once Wi-Fi or cellular connectivity is restored, the queue sync worker flushes pending events in batch payloads (up to 50 events per batch) to the backend API.
* **Idempotency Guarantee**: Because every scan event carries a unique client UUID key, network retries or duplicate uploads are deduplicated safely by the server without double-counting.

## Monitoring Sync Status

On the top header of the Vritti Lens scanning screen:

* **Green Cloud Icon**: Fully synchronized. All events pushed to server.
* **Orange Cloud Icon + Number (e.g. 14)**: Offline mode. Number indicates pending events stored in local queue.
* **Red Warning Icon**: Sync error or invalid credentials. Tap to open diagnostic PIN screen.