[General] Need manually controlled checkpointing at each turn, restore ability and fork ability.

**Mood:** 😔
**Category:** General

Need manually controlled checkpointing at each turn, restore ability and fork ability. Why is every Github Copilot experience except the one in VS Code missing this most basic and useful functionality? It should be the first thing added.

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| Field | Value |
| --- | --- |
| App version | 1.0.0 |
| OS | Windows 10.0.26100 |
| Theme | Noctis Azureus |
| Path | /chat |
| Tenure | Week 2 |

从 /chat 体验开始，这是 issue 中提到的唯一入口点，并跟踪当前如何处理各轮交互和对话状态。没有确定任何文件或测试；要视为完成，需要就手动创建检查点、恢复检查点以及 fork 对话时的行为达成一致。

由索引模型根据 Issue 内容生成。