update(design): Add Design for Durable Storage

[Meggielqk]

No description provided.

[Copilot]

Pull Request Overview

This PR adds comprehensive design documentation for EMQX's Durable Storage (DS) feature. The documentation explains the architecture, data hierarchy, read/write paths, and use cases for durable sessions and shared subscriptions.

Key Changes

• Added new design documentation for Durable Storage in three languages (English, Chinese, and Japanese)
• Updated durability introduction documents to include references to the new design documentation
• Enhanced architecture explanations with new concepts: Database, Slab, and TTV (Topic-Timestamp-Value)
• Added real-time subscription diagrams and transaction flow documentation

Reviewed Changes

Copilot reviewed 6 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
en_US/design/durable-storage.md	New comprehensive English design document explaining DS architecture, backends, hierarchy, write/read paths, and applications
zh_CN/design/durable-storage.md	Chinese translation of the design document with detailed explanations of DS concepts and implementation
ja_JP/design/durable-storage.md	Japanese translation matching the English design document structure
en_US/durability/durability_introduction.md	Updated to reference the new design doc, clarified "built-in" spelling, expanded architecture section with Database, Slab, and TTV concepts
zh_CN/durability/durability_introduction.md	Chinese version updated with similar enhancements and cross-reference to design doc
en_US/design/assets/real-time_subscriptions.png	New diagram illustrating real-time subscription architecture (binary PNG file)
zh_CN/design/assets/real-time_subscriptions.png	Chinese version of the real-time subscriptions diagram (binary PNG file)
ja_JP/design/assets/real-time_subscriptions.png	Japanese version of the real-time subscriptions diagram (binary PNG file)
dir.yaml	Added new design/durable-storage entry to the documentation navigation structure

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[ieQu1]

Hi,

Currently the structure of the documents has some duplication. I think the documentation should be restructured like that:

1. "Durability Introduction" document that contains high level information on how durability is used to implement persistent sessions, shared subscriptions, etc. Everything that concerns the end user. Ideally, it should not mention terms like "shard", "TTV", etc. Also it would great to minimize usage of term "stream" in the first document to avoid confusion with the new "MQTT streams" feature.
2. "Durable Storage Design". This document should contain all the technical details. It can mention streams (perhaps calling them "durable storage streams" to avoid confusion with other features).

[Copilot]

Pull Request Overview

Copilot reviewed 6 out of 14 changed files in this pull request and generated no new comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull Request Overview

Copilot reviewed 6 out of 15 changed files in this pull request and generated no new comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.