What
The diff pane shows how files have changed. It used to run one git command per file to fetch those changes. It now runs a single git command covering many files at once, and retries file by file for any paths whose output could not be read. The pane also records when it is shown, and how it opens has been fixed.
Why
Fewer git processes run when many files have changed.
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The writer flagged doubt
Whether the diff pane is available to everyone or behind a switch is not shown.