mergetool.vimdiff.layout behavior differs from documentation

Hello,

This is my first time reporting an issue with Git. I am not a native English speaker, so I apologize if there are any translation mistakes.

Below is my response to `git bugreport`:

1. I checked the `git mergetool --help` documentation and configured
`$ git config --global mergetool.vimdiff.layout "@REMOTE"`.
2. In a repository with merge conflicts, I opened vimdiff using `git
mergetool`, updated the REMOTE buffer, and saved the changes.

I expected the changes made to the REMOTE buffer to be reflected in the file.

The changes made to the REMOTE buffer were **not** reflected in the file.

The documentation states: ”@ is used to indicate the file containing the final version after solving the conflicts. If not present, MERGED will be used by default.” So I thought that the changes made to the REMOTE buffer will be reflected in the file if I use @REMOTE. However, in my tests, @LOCAL and @MERGED worked as expected, but @BASE and @REMOTE did not behave correctly.

I’ve uploaded a video reproducing this issue to a GitHub Gist. Please check here: https://gist.github.com/kawarimidoll/3e603664432702e434c27f343fb35f85

[System Info]
git version:
git version 2.48.1
cpu: aarch64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /nix/store/3z1jypscq2ld48kl089ywgwd8ri2rjxq-bash-5.2p37/bin/bash
feature: fsmonitor--daemon
libcurl: 8.12.1
OpenSSL: OpenSSL 3.4.1 11 Feb 2025
zlib: 1.3.1
uname: Darwin 24.3.0 Darwin Kernel Version 24.3.0: Thu Jan  2 20:24:23
PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T8122 arm64
compiler info: clang: 19.1.7
libc info: no libc information available
$SHELL (typically, interactive shell): /bin/zsh

I appreciate your time in reviewing this. Thank you!

kawarimidoll
GitHub: https://github.com/kawarimidoll