Finish a sibling comparison when a shared entry cannot be read [patch]

[matt-edmondson]

Fixes #436

What was wrong

DiffRepos read every tracked path that both siblings share through ReadFileOrEmpty, which caught only FileNotFoundException and DirectoryNotFoundException. A submodule's gitlink is a directory on disk, so File.ReadAllText threw UnauthorizedAccessException out of the background task CompareSiblingsAsync starts. Nothing observes that task, so SimilarReposPending stayed true, the panels showed "Comparing repositories..." indefinitely, and nothing was logged. A locked or permission-denied file took the same path.

Change

• TryReadTrackedFile replaces the read. It never throws:
  • a directory (gitlink, or a tracked link to a directory) reports no content and no reason
  • a missing file still reads as empty, as before
  • an IOException or UnauthorizedAccessException reports no content, with the exception's message as the reason
• DiffRepos leaves out any shared path that either side can't supply content for, and logs the reason when there is one: Left <file> out of the comparison with <remote>: <reason>. Gitlinks are skipped silently, since a shared submodule is normal. DiffAgainstAll gained an optional log parameter, which CompareSiblingsAsync passes through.
• CompareSiblingsAsync now catches anything that still escapes (IOException, UnauthorizedAccessException, InvalidOperationException, ArgumentException). It publishes an empty answer so the pending state always ends, and logs Comparing <remote> failed: <message>.
• DiffSingleFile, which runs on the render thread, goes through the same non-throwing read via ReadFileOrEmpty.

Tests

Two new tests in SimilarReposTests, both covering the acceptance criteria:

• SiblingsSharingASubmodulePathCompareWithTheGitlinkLeftOut adds a 160000 gitlink at external to both repos with git update-index --cacheinfo. It checks that the comparison finishes, that shared.txt is diffed, and that external is not.
• ASharedFileThatCannotBeReadIsLeftOutAndLogged holds the sibling's locked.txt open with FileShare.None, which is refused even under root. It checks that the comparison finishes, the readable file is still diffed, the locked one is left out, and the log names it.

Results:

• With the ProjectDirector.cs change reverted, both tests fail with the issue's exceptions: UnauthorizedAccessException: Access to the path '.../external' is denied and IOException: ... being used by another process.
• With the change, 105 of 107 pass and 1 is skipped. The one failure is CloningAnLfsRepositoryRestoresTheFileContentRatherThanThePointer, which fails the same way on unchanged main in this sandbox.
• The build has no warnings. dotnet format reports only the two issues that already exist on main (import ordering, IDE0001 at line 1218).

🤖 Generated with Claude Code

https://claude.ai/code/session_01CaZMWc5xm4vDRcyMefDXyV

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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