Accept diff writes to wrong path when using `set autochdir`

[mikeboiko]

Description

When set autochdir is enabled, accepting a diff sometimes writes to the wrong file path.

Specifically, when switching folders, the CopilotChat buffer’s working directory does not update correctly, which causes diffs to be applied to the wrong file.

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Steps to Reproduce

1. Enable set autochdir in Neovim.
2. Open file ~/git/Test/names1.json.
3. Open Copilot Chat, run pwd inside the CopilotChat window → directory is ~/git/Test.
   • ✅ Accepting a diff at this point works as expected.
4. Now open another file in a different folder (in the original window): ~/git/Test/test/names2.json.
5. Run pwd inside the CopilotChat window → directory is still ~/git/Test (does not change).
6. Ask a question in Copilot Chat and accept the diff.

Expected:
The diff should be written to ~/git/Test/test/names2.json.

Actual:
The diff is incorrectly written to ~/git/Test/names1.json.

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Environment

• Neovim version:

NVIM v0.11.3
Build type: RelWithDebInfo
LuaJIT 2.1.1753364724
Run "nvim -V1 -v" for more info

• CopilotChat.nvim version: main/72216c06fa2ce82406c3406d898a83c02db412a7
• OS: Linux

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Additional Notes

• It seems the working directory inside CopilotChat is not updating properly with autochdir. This causes mismatches between the current buffer path and where diffs are applied. If I disable autochdir in `nvim, everything starts working properly.
• I don't remember when this started being an issue, but this didn't occur at one point.
• Love the plugin... keep up the great work!

[deathbeam]

Hopefully #1378 solves this. It is a bit tricky because when the cwd changes so do the references in chat. Before I was forcing file picker to always grab absolute paths so they can be provided directly to caht and avoiding relative paths, but I changed the file picker to just use relative paths recently and I assume that is what broke this (plus there were some workarounds before). So now I just force the LLM to always try to generate absolute path (but this is kinda error prone obviously still because it relies on LLM not hallucinating much)

[mikeboiko]

Thank you so much for fixing this issue so quickly! I just confirmed and it's working great with absolute paths.