[Requests and ideas] Global always-on skills for the Copilot desktop app chat

**Mood:** 😊
**Category:** Requests and ideas

Problem:
The Copilot desktop app doesn't support auto-invocation of personal skills in the chat interface. Skills stored in ~/.copilot/skills/ with descriptions like "Apply this in all interactions" are only auto-discovered in VS Code agent mode, the cloud agent, and Copilot CLI — not in the app's chat.

This means users have to manually invoke their context skill at the start of every new chat session, which is friction that VS Code users don't have (via applyTo: '**' in global prompt files).

Request:
Support a mechanism in the Copilot desktop app chat to mark a personal skill as always-on — either via:

A frontmatter flag in SKILL.md (e.g. always: true)
A global instructions file (e.g. ~/.copilot/instructions.md)
Honouring descriptions like "Apply this in all interactions" as an auto-invoke trigger
Impact:
Users who have personalised Copilot with identity, coding standards, and workflow rules have to re-establish that context on every new chat. This is a significant usability gap vs VS Code.

---
| Field | Value |
| --- | --- |
| App version | 0.2.14 |
| OS | Windows 10.0.26200 |
| Theme | Noctis Azureus |
| Path | /chat |
| Tenure | Day 1 |

首先检查桌面应用的 /chat 行为，以及 ~/.copilot/skills/ 下的个人 skill 文件，包括 SKILL.md 描述。比较所请求的始终启用机制，并将完成定义为：提供一种受支持的方式，使个人 skill 或全局指令能够在新的聊天会话中自动应用。

由索引模型根据 Issue 内容生成。