Storybook: Include playground stories and MDX in CI smoke tests

[mirka]

What?

Stop excluding playground stories and top-level Storybook MDX files from the CI smoke test build (NODE_ENV=test).

Why?

The smoke test workflow (storybook-check.yml) runs with NODE_ENV=test, while the GitHub Pages deploy uses NODE_ENV=production. The conditionals in storybook/main.ts meant CI only built a subset of stories, so production-only build failures could slip through. This gap recently caused a merged PR to pass CI while breaking the Storybook Pages deploy.

Benchmarking locally shows the exclusions save only ~1 second of storybook build time (~1.5%), so the coverage trade-off is likely not worthwhile, even on CI.

The NODE_ENV === 'test' story exclusions date back to the Storybook 5.3 era (#19599), where they were used for Storyshots. They were carried forward through later Storybook upgrades (#53520, #74396) without a documented rationale tied to current CI.

#69679 added the smoke test workflow but did not introduce these conditionals or set NODE_ENV in CI. Until #74626 wired up NODE_ENV: test in storybook-check.yml, the exclusions were likely not even taking effect in CI. #74626 narrowed them from all ./stories/** files to playground stories and top-level MDX, and added the comment about speed and redundancy during review. That PR was primarily about enabling the components manifest.

How?

Always include ./stories/playground/**/*.story.@(jsx|tsx) and ./stories/**/*.mdx in the stories glob list.

Note

You may be asking, should we stop doing NODE_ENV=test for the CI run then? My conclusion is no, because the main difference remaining between test and production is minification, and that indeed does contribute a non-negligible amount of time (~8s).

Testing Instructions

1. Confirm CI "Storybook build and Smoke Tests" passes on this PR.
2. Optionally compare build times: NODE_ENV=test npm run storybook:build before and after.

[github-actions]

Size Change: 0 B

Total Size: 7.5 MB

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[github-actions]

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Co-authored-by: mirka <[email protected]>
Co-authored-by: aduth <[email protected]>
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[github-actions]

Flaky tests detected in b853fe2.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/28044830276
📝 Reported issues:

• [Flaky Test] shows post-locked modal when document size limit is exceeded #78753 in /test/e2e/specs/editor/collaboration/http-only/collaboration-document-size-lock.spec.ts

[aduth]

Thanks for the context in tracking down the history here. At least as far as my own recent contributions are concerned, as mentioned it was largely carrying forward what had already existed, and adding documentation to clarify what my own interpretation of the exclusions would have been intended for, without critically considering whether they're valuable. If they're not contributing meaningfully to build times and this has proven to have caused errors on trunk, it seems reasonable (and simpler overall) to remove the exclusion.

Also good to clarify about the impact of potentially using 'production' here, to "fully" recreate a trunk build. Given that has a more noticeable impact on build times and the minification itself doesn't seem quite as prone to issues, seems reasonable to keep NODE_ENV: test for now.