Core: Reload the preview-iframe when tearing down a story during loading

[JReinhold]

Closes #26723

Works on #26637

Originally proposed in #26649 (comment)

What I did

• Added the loading phase to the phases that will trigger a full iframe reload if it isn't finished within 3 ticks. The list of phases already included rendering and playing
• Added tests for this.

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

Manual testing

1. In a React sandbox add the following RaceConditions.stories.tsx file:

import { expect } from "@storybook/test";

const delay = (ms) => new Promise((resolve) => { setTimeout(resolve, ms)});

export default {
    title: "Race Conditions"
};

let myVariable = "";

export const FastLoader = {
    loaders: async () => {
        await delay(1000);
        myVariable = 'fast';
    },
    render: () => {
        return <div>Rendered: {myVariable}</div>
    }
};

export const SlowLoader = {
    loaders: async () => {
        myVariable = 'slow';
        await delay(3000);
        myVariable += '-end';
    },
    render: () => {
        return <div>Rendered: {myVariable}</div>
    }
};

3. Open the "Fast Loader" story, and while it is still loading, navigate to the "Slow Loader" story.
4. The story should say "slow-end" and not "fast-end" as it does currently.

Documentation

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

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/src/sandbox-templates.ts

• 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

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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[tmeasday]

This is great (++ tests). I have a suggestion on how to tweak the test (same suggestion applies to all three) that might make it a little more in line with what actually might happen.

[tmeasday]

LGTM

[kasperpeulen]

This looks great!
1 line change in implementation and 150 lines of added code in tests! 🔥