Add integration tests for nonexistent package caching and invalid log file path

[Copilot]

Two error paths in RunToolLogic and Context.OpenLogFile had no integration test coverage.

Description

• IntegrationTest_CacheNonexistentPackage_ReturnsError — exercises the path where NuGetCache.EnsureCachedAsync throws InvalidOperationException for an unknown package; asserts non-zero exit code and "Error" in output
• IntegrationTest_LogFlag_WithInvalidFilename_ReturnsError — exercises Context.OpenLogFile failure by passing a path into a nonexistent directory (/nonexistent_dir_xyz_abc/invalid.log); asserts non-zero exit code and "Error" in output. Path is a hard-coded const — no Path.Combine — to avoid CodeQL path-traversal alerts; works cross-platform since Windows resolves root-relative paths to the current drive.
• requirements.yaml — linked new tests to NC-CLI-009 (error reporting) and NC-CLI-007 (log flag)

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code quality improvement

Pre-Submission Checklist

Build and Test

• Code builds successfully: dotnet build --configuration Release
• All unit tests pass: dotnet test --configuration Release
• Self-validation tests pass:
  dotnet run --project src/DemaConsulting.NuGet.CacheTool --configuration Release --framework net10.0
--no-build -- --validate
• Code produces zero warnings

Code Quality

• Code formatting is correct: dotnet format --verify-no-changes
• New code has appropriate XML documentation comments
• Static analyzer warnings have been addressed

Quality Checks

• Spell checker passes: cspell "**/*.{md,cs}"
• Markdown linter passes: markdownlint "**/*.md"
• YAML linter passes: yamllint .

Testing

• Added unit tests for new functionality
• Updated existing tests if behavior changed
• All tests follow the AAA (Arrange, Act, Assert) pattern
• Test coverage is maintained or improved

Documentation

• Updated README.md (if applicable)
• Updated ARCHITECTURE.md (if applicable)
• Added code examples for new features (if applicable)
• Updated requirements.yaml (if applicable)

Additional Notes

Test count increases from 43 to 45 per framework (.NET 8/9/10). CodeQL reports 0 alerts.

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[Malcolmnixon]

This Path.Combine will trigger CodeQL issues. Consider hard-coding the full path.

[Copilot]

Fixed in 886a817 — replaced Path.Combine(Path.GetTempPath(), ...) with fully hard-coded platform-specific paths:

var invalidLogPath = OperatingSystem.IsWindows()
    ? @"C:\nonexistent_dir_xyz_abc\invalid.log"
    : "/nonexistent_dir_xyz_abc/invalid.log";

CodeQL confirms 0 alerts.