**Grade: 8**

### Bugs
- There are no explicit bugs in the given code. However, it is important to ensure data integrity between `CodingData` and `UnreadNumbers`.

### Optimizations
- The `CodingData` structure could implement a custom initializer that ensures that `all` in `UnreadNumbers` is equal to the sum of other properties if that is a business requirement.
- Consider renaming the `subs` property in `CodingData` to `subscriptions` to keep consistency across structures.

### Good points
- The code is well-structured, with appropriately named components.
- The use of `Decodable`, `Hashable`, and `Sendable` protocols enhances the versatility and functionality of the `UnreadNumbers` struct.
- Consistent use of access control modifiers (`public`) for properties and initializers where necessary.
- Efficient transformation from `CodingData` to `UnreadNumbers` using the `decoded` computed property.

### Summary
The code snippet provides a well-crafted extension of a `NotificationFeed` class to manage unread notifications efficiently. It is well-structured, establishing clear separation of concerns particularly through the use of Codable structures for decoding and ensuring compatibility with concurrency through the `Sendable` protocol. Minor consistency improvements with property naming and initializing could enhance the code's robustness and readability further.

### Open source alternatives
- [Rocket.Chat](https://github.com/RocketChat/Rocket.Chat) provides notification features that can be extended or used as a reference.
- [Mattermost](https://github.com/mattermost/mattermost-server) also deals with notifications and could provide additional perspective on handling unread notification counts effectively.