# Design Spec — Notification Center

**Author** S. Adeyemi · **Reviewers** Platform, Mobile · **v1.2**

## Overview

A unified in-app notification center replacing the three
ad-hoc toast systems currently shipped across web and mobile.

## Goals

- One delivery pipeline, one read-state model
- p95 delivery latency under 2 seconds
- Full parity between web and mobile clients

## Non-goals

Email and push digests — handled by the existing comms service.

## Requirements

| ID  | Requirement                            | Priority |
| --- | -------------------------------------- | -------- |
| N-1 | Real-time delivery via existing socket | P0       |
| N-2 | Read/unread sync across devices        | P0       |
| N-3 | Per-category mute controls             | P1       |
| N-4 | 90-day retention with archive          | P2       |

## User flow

1. Event published to the notification topic
2. Fan-out service resolves audience and preferences
3. Client receives payload; badge count updates optimistically

> **Edge case:** a mute applied mid-flight must win — check
> preferences at delivery, not at publish.

## Acceptance criteria

Delivery p95 < 2s at 10× current event volume; zero cross-user
leakage in the fan-out audit; mute honored within one event.