Core: Fix iframe URL issues and Addons display for /index.html

[ia319]

Closes #33548

What I did

• url.ts: Added normalizeToDirectory to extract directory paths from a pathname. Converts file paths like /index.html to / while keeping directory paths unchanged. Fixes iframe URL concatenation errors.
• refs.ts: Uses the normalized directory path to determine sourceType, preventing local sources from being misclassified as external.

Another error in the latest code

Phenomenon: When accessing /index.html, the iframe keeps loading indefinitely.

Cause:
getStoryHrefs directly concatenates ${location.pathname}iframe.html. When pathname is /index.html, the generated iframe URL becomes /index.htmliframe.html, causing a 404 error.

Addons not displaying

Phenomenon: Accessing /index.html loads the page normally, but the top toolbar and Addons panel are missing.

Cause:
When accessing /index.html, getSourceType misclassifies it as external (because it compares the full pathname), causing the navigate redirect to be skipped. The URL remains at ?path=/, so Addons do not display due to a viewMode mismatch.

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. Run:

yarn task --task compile

2. In the sandbox, build and run the sandbox static service:

yarn build-storybook
python3 -m http.server 8000 --directory storybook-static

3. Access http://localhost:8000/index.html to confirm that the automatic redirect works and Addons are displayed correctly.

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-storybook/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 publish.yml --field pr=<PR_NUMBER>

Summary by CodeRabbit

• Refactor
  • Enhanced path normalization and improved consistency in source type detection logic.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

A new directory path normalization utility function is introduced, and existing path comparison logic is refactored to use directory-based path comparison instead of full URL paths for determining local versus external sources.

Changes

Cohort / File(s)	Summary
Path normalization utilities code/core/src/manager-api/modules/url.ts, code/core/src/manager-api/modules/refs.ts	Introduces normalizeToDirectory() utility function for converting pathnames to directory paths with trailing slashes. Updates getSourceType() in refs.ts to compare normalized directory paths instead of full URLs when detecting local sources. Refactors url.ts to use derived basePath for consistent directory-normalized path handling in origin and manager base calculations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

✨ Finishing touches

• 📝 Generate docstrings

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[ia319]

Why isn't CodeRabbit working on this PR

[storybook-app-bot]

Package Benchmarks

^{Commit: d9ebb3d, ran on 26 January 2026 at 14:31:24 UTC}

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[JSMike]

FYI, I pushed separate PR for this, I added @ia319 as co-author. #33686

[ghengeveld]

I think this was already fixed here. Sorry I hadn't seen this PR when I fixed my own mess, otherwise I would've attributed y'all.

[ia319]

Related issues have been fixed