Storybook: Handle production module load failures

[ciampo]

What?

Makes the production Storybook more resilient to intermittent dynamic module load failures.

Why?

The production site can request hundreds of story dependencies at once. A single transient GitHub Pages or CDN failure causes the complete story import to fail, even when the story module itself returns 200.

How?

• Disables Vite's eager JavaScript module preloading so the browser discovers the dependency graph incrementally.
• Handles Vite's vite:preloadError with one guarded full-page reload.
• Lets a repeated failure within 60 seconds surface normally instead of creating a reload loop.

See Vite's load error handling guidance.

Testing Instructions

1. Run npm run storybook:build.
2. Serve storybook/build and open /?path=/story/design-system-components-menu--default.
3. Confirm that the Menu story renders.
4. In the preview iframe, dispatch window.dispatchEvent( new Event( 'vite:preloadError', { cancelable: true } ) );.
5. Confirm that the full Storybook reloads once and the Menu story renders again.
6. Dispatch the same event again within 60 seconds.
7. Confirm that the page does not reload again.

Testing Instructions for Keyboard

Not applicable. This changes Storybook asset loading and does not change keyboard interaction.

Screenshots or screencast

Here's what the typical failure looks like

Use of AI Tools

This pull request was implemented with Codex. The investigation used browser inspection, a HAR export, generated build analysis, and local automated verification. The author reviewed the resulting changes.

[github-actions]

Size Change: 0 B

Total Size: 7.74 MB

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[github-actions]

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[github-actions]

Flaky tests detected in 4559721.
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/32358276178
📝 Reported tests:

inserts a block in proper place after having clicked `Browse All` from block appender in /test/e2e/specs/editor/various/inserting-blocks.spec.js, passed after 1 failed attempt.

Error: apiRequestContext.fetch: socket hang up
Call log:
  - → GET http://localhost:8889/wp-json/wp/v2/blocks?per_page=100&status=publish%2Cfuture%2Cdraft%2Cpending%2Cprivate%2Ctrash
    - user-agent: Playwright/1.62.1 (x64; ubuntu 24.04) node/20.20 CI/1
    - accept: */*
    - accept-encoding: gzip,deflate,br
    - X-WP-Nonce: 8cca09d5f1
    - cookie: wordpress_test_cookie=WP%20Cookie%20check; wordpress_logged_in_23778236db82f19306f247e20a353a99=admin%7C1787394238%7CHrGs9QCuvEOnzmaVYfjDLxHdn2jJM1SDxplEoisGFPm%7C0dba0995218fd4f4215c94f3c358ced7eec0aef5ff81bba82aca159cefb579b5; wp-settings-time-1=1787221439

    at RequestUtils.rest (/home/runner/work/gutenberg/gutenberg/packages/e2e-test-utils-playwright/src/request-utils/rest.ts:112:39)
    at RequestUtils.deleteAllBlocks (/home/runner/work/gutenberg/gutenberg/packages/e2e-test-utils-playwright/src/request-utils/blocks.ts:23:28)
    at /home/runner/work/gutenberg/gutenberg/test/e2e/specs/editor/various/inserting-blocks.spec.js:11:22