Vitest: Revert removal of workarounds obsoleted by the Vitest 4 floor

[obvious-autobuild]

Reverts #36188

What I did

This PR reverts #36188 (merge commit 32f2a8b), restoring the 8 affected Vitest-related files to their pre-merge state:

• code/addons/vitest/src/node/vitest-manager.ts
• code/addons/vitest/src/vitest-plugin/index.ts
• code/core/src/actions/loaders.ts
• code/core/src/babel/index.ts
• code/core/src/babel/vitest-config-helpers.test.ts
• code/core/src/babel/vitest-config-helpers.ts
• code/core/src/cli/AddonVitestService.test.ts
• code/core/src/cli/AddonVitestService.ts

Why: #36188 was automerged by obvious-autobuild[bot] immediately after review, without maintainer authorization. This revert takes next back to the pre-merge tree (verified: git diff HEAD 1720e5a29f3b5b9933aa7c9462839feaeb10152a over these paths is empty). The same changes will be re-landed through a fresh PR stacked on this branch. Merge of this PR must be performed by a human — do not enable auto-merge.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

The revert restores the unit tests removed by #36188 (code/core/src/babel/vitest-config-helpers.test.ts, code/core/src/cli/AddonVitestService.test.ts); CI runs them as part of this PR.

Manual testing

Caution

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

No manual testing is necessary: this PR only restores the exact pre-merge state of the affected files (tree-verified against 1720e5a), which is the state next had before #36188 merged. CI provides the verification.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

No documentation update needed: the revert returns the code to the pre-merge state.

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary Release - 🚫 Not run

This PR does not have a canary release associated.

In-repo PRs: add the ci:canary label. Later pushes republish while the label remains.

Fork PRs: the label does nothing (a later push must not auto-publish). A maintainer publishes from this repository with Run workflow and the pr input. branch and sha are optional; if more than one is set, they must be the same commit. The fork author does not need to do anything.

🔗 Obvious Project · 🧵 Obvious Thread