Add platform validation for multi-arch manifests in Post_Build stage

[dagood]

Change createManifestList to validate the list of platforms in the manifest list against the expectations in manifest.json. More information in doc changes.

• Fixes Add pre-publish validation that ensures shared tag manifests include all expected platforms defined by manifest.json #2127

[Copilot]

Pull request overview

Adds an optional platform-completeness validation step for multi-arch manifest list generation in ImageBuilder and wires it through AzDO Post_Build templates (plus docs) so builds can fail early if a manifest list tag would omit manifest-defined platforms.

Changes:

• Add manifest list platform validation APIs to ManifestListHelper and expose a --validate-manifest-list-platforms CLI switch for createManifestList.
• Update CreateManifestListCommand to run validation (when enabled) before pushing/creating manifest lists.
• Plumb a validateManifestListPlatforms boolean parameter through AzDO templates and document the behavior in DEV-GUIDE/CHANGELOG.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/ImageBuilder/ManifestListHelper.cs	Adds platform validation logic and supporting types/helpers for manifest list generation.
src/ImageBuilder/Commands/CreateManifestListOptions.cs	Introduces --validate-manifest-list-platforms CLI option and binds it to options.
src/ImageBuilder/Commands/CreateManifestListCommand.cs	Executes platform validation (when enabled) before creating/pushing manifest lists.
src/ImageBuilder.Tests/ManifestListHelperTests.cs	Adds unit tests covering validation issues and successful validation.
src/ImageBuilder.Tests/CreateManifestListCommandTests.cs	Adds end-to-end command test verifying validation prevents partial manifest list creation.
eng/docker-tools/templates/stages/dotnet/build-test-publish-repo.yml	Adds validateManifestListPlatforms parameter pass-through for the repo pipeline template.
eng/docker-tools/templates/stages/dotnet/build-and-test.yml	Adds validateManifestListPlatforms parameter pass-through for dotnet build-and-test stage template.
eng/docker-tools/templates/stages/build-and-test.yml	Wires validateManifestListPlatforms into Post_Build stage invocation.
eng/docker-tools/templates/jobs/post-build.yml	Conditionally appends --validate-manifest-list-platforms to createManifestList args.
eng/docker-tools/DEV-GUIDE.md	Documents Post_Build creating manifests and the new validation toggle guidance.
eng/docker-tools/CHANGELOG.md	Adds changelog entry describing the new validation parameter and recommended usage.

[dagood]

This is an implementation by Copilot for:

• Add pre-publish validation that ensures shared tag manifests include all expected platforms defined by manifest.json #2127

The doc and test changes look reasonable to me, but I would need more time to understand everything happening in src/ImageBuilder/ManifestListHelper.cs. I can't tell at first glance if Copilot's self-criticism is valid, for example.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.