Quoted() does not escape backslashes, corrupting process arguments #2796

Summary

StringExtensions.Quoted() (src/App.Extensions.cs) wraps a value in double quotes and escapes embedded ", but leaves backslashes untouched. Its result is assigned to ProcessStartInfo.Arguments, which .NET re-parses into argv using MSVC-style rules on every platform, where a backslash immediately before a double quote is significant.

As a result, a value that ends in a backslash, or contains a backslash directly before a quote, is handed to the child process (git) as a different string than the input.

Impact

A file whose name ends in a backslash is legal on macOS and Linux. Such a path reaches commands that place the filename last with no --, e.g.:

• src/Commands/QueryFileContent.cs — show {rev}:{file}
• src/Commands/SaveRevisionFile.cs — show {rev}:{file}
• src/Commands/QueryFileSize.cs — cat-file -s {rev}:{file}

Viewing or saving that file from history then operates on the wrong path or fails. Two-argument commands such as Move (mv -v {old} {new}) can have the first path swallow the second.

This is a data-integrity / quoting-correctness bug. It is not a shell: arguments are passed via UseShellExecute = false, so no shell metacharacters are involved.

Reproduction

Round-trip the current Quoted() output through .NET's own argument parser:

Plain names, names with spaces, and a lone embedded quote round-trip correctly.

Suggested fix

Escape the value the same way .NET itself does when building an argument (System.PasteArguments): double any run of backslashes that precedes a quote or the closing quote. This fixes every call site at once, since they all funnel through Quoted() into Args.

A PR implementing this, with a standalone round-trip test that checks the invariant against .NET's real argument parser, follows.