With LocalPath set to a subdirectory, Unstage and Apply().ToIndex() exit 0 and change nothing, and ForPath filters return empty #178

What's wrong

GitRepository.LocalPath is a public init property, and nothing requires it to be the top of the working tree. IsClonedAsync uses rev-parse --is-inside-work-tree, which also answers true for a subdirectory, so a repository opened at a subdirectory looks valid.

Every verb then runs git -C <LocalPath> --literal-pathspecs … (GitIntegration/GitRepository.cs, Builders/GitCommandBuilder.cs). The paths are mismatched:

• Status(), Diff() and Patch() report paths relative to the repository root, which is how RelativeFilePath is documented.
• Git reads pathspecs relative to the -C directory.
• git apply run from a subdirectory silently skips any patched path outside that directory, and still exits 0.

Failure scenario (reproduced with git 2.43)

The repo contains root.txt and sub/s.txt. Open it with new GitRepository { LocalPath = <repo>/sub }:

• Apply: Apply(patch).ToIndex() with a patch touching root.txt runs git -C sub apply --cached <tmp>. It exits 0, and git diff --cached is empty. The caller is told the hunk was staged.
• Unstage: stage sub/s.txt, then call Unstage("sub/s.txt"), the path exactly as Status() reported it. That runs git -C sub --literal-pathspecs reset -q -- sub/s.txt, which exits 0, and the file is still staged.
• Log/Diff/Patch/RevList: .ForPath("sub/s.txt") silently returns empty results.
• Add: Add().ForPath("sub/s.txt") at least fails loudly (pathspec did not match, exit 128).

Suggested fix

Either:

• (a) Resolve paths from the root whatever -C is: use :(top,literal)<path> pathspec magic in place of the global --literal-pathspecs, and run apply from rev-parse --show-toplevel; or
• (b) Make the requirement explicit: document that LocalPath must be the working-tree root, and enforce it. For example, verbs that take paths would probe rev-parse --show-prefix and throw when it is non-empty.

Acceptance criteria

• An integration test opens a repository at a subdirectory. It shows that Unstage, Apply().ToIndex() and the ForPath filters either act on root-relative paths correctly or fail loudly.
• None of these operations reports success while making no change.