PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines:https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Headless mode is currently supported only forkarma viabrowsers: [ 'ChromeHeadless', 'FirefoxHeadless' ]. However, it is not supported for Vitest browser mode. SeeHeadless for more information.

I considered two solutions for Vitest:

Solution 1 (Committed / Implemented):

This solution is compatible with how Karma handles headless mode, allowing for migration without configuration changes:

"options": {"tsConfig":"tsconfig.spec.json","buildTarget":"::development","runner":"vitest","browsers": ["ChromiumHeadless"]}

Solution 2:

Introduce a newheadless property in the schema. This approach is not compatible with Karma without a breaking API change:

"options": {"tsConfig":"tsconfig.spec.json","buildTarget":"::development","runner":"vitest","headless":true,"browsers": ["chromium"]}

The issue with Solution 2 is that it is not compatible with Karma, which uses'ChromiumHeadless' /'FirefoxHeadless' to enable headless mode.

Issue Number:#30681

What is the new behavior?

The builder can now convert the Karma headless configuration format to the Vitest format and activate headless mode accordingly.

Does this PR introduce a breaking change?

• Yes
• No

Other information

TODO: If the solution makes sense, I will write the docs and tests for it