Provide clear error when directory does not exist

[johnterickson]

Context

There is lots of confusion from cryptic tar errors for the simple case that the directory to archive does not exist see #12892

tar: could not chdir to 'C:\cargo_target_dir'
...
##[error]Process returned non-zero exit code: 1

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Description

This adds a clear error message of when the directory does not exist.

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Risk Assessment (Low / Medium / High)

Low - this is already a failure path

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Unit Tests Added or Updated (Yes / No)

Yes

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Additional Testing Performed

None

[Copilot]

Pull Request Overview

Adds a clear check and error message when the input directory does not exist in the tar‐archiving utility, along with a corresponding unit test.

• Introduce Directory.Exists validation in TarUtils.ArchiveFilesToTarAsync
• Throw a DirectoryNotFoundException with a descriptive message for nonexistent paths
• Add an L0 test to verify the new exception behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Agent.Plugins/PipelineCache/TarUtils.cs	Added a precondition to check for directory existence and throw a clear error
src/Test/L0/Plugin/TarUtilsL0.cs	Added an L0 test to assert that a missing directory throws the expected exception

Comments suppressed due to low confidence (2)

src/Test/L0/Plugin/TarUtilsL0.cs:26

• [nitpick] The test method name is a bit verbose and includes an unnecessary Tar_ prefix. Consider renaming to ArchiveFilesToTarAsync_NonexistentDirectory_ThrowsDirectoryNotFoundException to match standard naming conventions.

public async Task Tar_ArchiveFilesToTarAsync_ThrowsDirectoryNotFoundException()

src/Agent.Plugins/PipelineCache/TarUtils.cs:41

• [nitpick] The exception message here uses single quotes around the path, whereas the file-path check above does not. For consistency, align the formatting of both messages (either both with quotes or both without).

throw new DirectoryNotFoundException($"Please specify path to a directory, '{inputPath}' does not exist.");

[fadnavistanmay]

/azp run

[azure-pipelines]

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