fix(copilot): Prioritize XDG_CONFIG_HOME for OAuth token references on Windows

[hat0uma]

Overview

This PR fixes an issue where, on Windows environments with XDG_CONFIG_HOME set, Copilot's OAuth token cannot be found, resulting in the following error:

...m-data/lazy/avante.nvim/lua/avante/providers/copilot.lua:293: You must setup copilot with either copilot.lua or copilot.vim

The detailed stack trace is as follows:

- avante.nvim\lua\avante\providers\copilot.lua:120 _in_ **get_oauth_token**
- avante.nvim\lua\avante\providers\copilot.lua:293 _in_ **setup**
- avante.nvim\lua\avante\providers\init.lua:164 _in_ **setup**
- avante.nvim\lua\avante\providers\init.lua:317 _in_ **setup**
- avante.nvim\lua\avante\init.lua:367 _in_ **setup**

Cause

On Windows, the current implementation attempts to load the authentication file (hosts.json , apps.json) from:

~/AppData/Local/github-copilot/

However, if XDG_CONFIG_HOME is set, the file is actually generated at:

$XDG_CONFIG_HOME/github-copilot/

As a result, the OAuth token cannot be retrieved and the above error is triggered.

Changes

• The code now checks XDG_CONFIG_HOME first on all platforms.
• If the file is not found there, it falls back to the existing logic (on Windows, ~/AppData/Local).

This behavior aligns with how copilot.lua currently works:

https://github.com/zbirenbaum/copilot.lua/blob/886ee73b6d464b2b3e3e6a7ff55ce87feac423a9/lua/copilot/auth.lua#L171

https://github.com/zbirenbaum/copilot.lua/blob/886ee73b6d464b2b3e3e6a7ff55ce87feac423a9/lua/copilot/auth.lua#L134-L151

Repro

1. On Windows, define the XDG_CONFIG_HOME environment variable and point it to any directory.
2. Sign in to Copilot so that $XDG_CONFIG_HOME/github-copilot/apps.json is generated.
3. Apply the following configuration:

   require("avante").setup({
     provider = "copilot",
   })