Fix unwanted events when diffing untracked files

[eamodio]

Fixes an issue where diffing untracked files could trigger unwanted file system events.

Summary

Uses a temporary index for diffs of untracked files to avoid side effects.

Impact

Users working with untracked files in the Commit Composer no longer experience unexpected behavior from file system event triggers.

Validation

1. Open a repository with untracked files
2. Use the Commit Composer to view diffs of untracked files
3. Verify no unexpected events or side effects occur

Risk

Low - isolated change to diff operation handling.

[nikolay-1986]

Warning on updates.odt

@eamodio - I have two questions related to the scope of this issue

1. I'm observing the periodic appearance of a warning (marked in red) in the git events output, which triggers a message about a change in the working directory state, even though I haven't performed any actions. I simply open the Commit Composer, and after a while, the warning message appears. There's also a constant part (I guess updates) (marked with a green border) that repeats periodically but doesn't trigger a refresh of the working directory state.

I'm not sure if the cause lies in the repository state - this is my public repository gk-gl-test-github with many test entries. For vscode-gitlens repository, this warning doesn't occur.

Should I investigate this behavior further for complete clarity?

2. After removing mentioned repository gk-gl-test-github from the VSCode workspace, upon the first VSCode restart (Ctrl+Shift+P --> Reload window), a Repository not found warning appears. On the second and subsequent restarts, the doInitialScan procedure doesn't return such a warning.

Is this normal behavior during cache update, or should I stop here and investigate in more detail?

2026-01-30 17:42:58.156 [info] > git rev-parse --show-toplevel [1056ms]
2026-01-30 17:42:58.158 [info] > git diff --name-status -z --diff-filter=ADMR --find-renames=50% f413fba3d35a6100af3b072648bd1555d175235e...refs/remotes/origin/main -- [795ms]
2026-01-30 17:42:59.242 [info] > git config --get commit.template [1087ms]
2026-01-30 17:42:59.478 [info] > git for-each-ref --format=%(refname)%00%(upstream:short)%00%(objectname)%00%(upstream:track)%00%(upstream:remotename)%00%(upstream:remoteref) --ignore-case refs/heads/main refs/remotes/main [1258ms]
2026-01-30 17:42:59.482 [info] > git rev-parse --show-toplevel [1314ms]
2026-01-30 17:43:00.479 [info] > git rev-parse --show-toplevel [984ms]
2026-01-30 17:43:00.741 [info] > git for-each-ref --sort -committerdate --format %(refname)%00%(objectname)%00%(*objectname) [999ms]
2026-01-30 17:43:01.087 [info] > git status -z -uall [1350ms]
2026-01-30 17:43:01.877 [info] > git rev-parse --show-toplevel [1221ms]
2026-01-30 17:43:02.806 [info] > git rev-parse --show-toplevel [921ms]
2026-01-30 17:43:02.811 [info] [Model][doInitialScan] Initial repository scan completed - repositories (1), closed repositories (0), parent repositories (0), unsafe repositories (0)
2026-01-30 17:43:02.812 [warning] [GitFileSystemProvider][readFile] Repository not found - git:/d%3A/Proj/GL/Testing-gl-rc-17.10/gk-gl-test-github/commit_test_2.txt?%7B%22path%22%3A%22d%3A%5C%5CProj%5C%5CGL%5C%5CTesting-gl-rc-17.10%5C%5Cgk-gl-test-github%5C%5Ccommit_test_2.txt%22%2C%22ref%22%3A%22~%22%7D
2026-01-30 17:43:02.812 [warning] [GitFileSystemProvider][stat] Repository not found - git:/d%3A/Proj/GL/Testing-gl-rc-17.10/gk-gl-test-github/commit_test_2.txt?%7B%22path%22%3A%22d%3A%5C%5CProj%5C%5CGL%5C%5CTesting-gl-rc-17.10%5C%5Cgk-gl-test-github%5C%5Ccommit_test_2.txt%22%2C%22ref%22%3A%22~%22%7D

[eamodio]

@nikolay-1986 Those logs are the VS Code Git extension, not GitLens.

This bug fix only handles a very specific case where you have untracked files with commit composer. Since before this fix, we'd stage/unstage the untracked files to get the diff causing repo events to get triggered (that we sometimes successfully "ignore", but often do not).

So we should not see "Index had changes" errors when opening Commit Composer when you have untracked files.

[axosoft-ramint]

Not seeing it trigger when in composer with an untracked file on the current prerelease.