Added urls:assets config option to serve static theme assets from CDN

[muratcorlu]

Ghost already supports CDN base URLs for uploaded content (urls:image, urls:media, urls:files), but static theme assets (/assets/* and /public/*) have always been served from the origin. This adds urls:assets to complete the picture.

When urls:assets is configured, all URLs produced by the {{asset}} helper and Ghost's own public asset tags (cards.min.js, member-attribution.min.js, etc.) are rewritten to use the CDN as the base instead of the origin.

Benefits:

• Improved page load performance: assets can load in parallel from origin domain
• Cookie-free domain: serving assets from a separate domain means browsers don't send session cookies with every asset request, reducing request overhead
• Easier CDN cache management: With the changes on Ghost, no need to drop CDN caches for assets.

Configuration:

  "urls": { "assets": "https://cdn.example.com/my-site" }

Theme assets resolve to:

  https://cdn.example.com/my-site/assets/css/screen.css

Public assets resolve to:

  https://cdn.example.com/my-site/public/cards.min.js

Note: when urls:assets is set, the Ghost subdirectory (if any) is not included in the asset URL. The CDN base URL is used as-is. This is aligned with current CDN url configurations for images, media and files. Installations running Ghost under a subpath (e.g. example.com/blog/) should ensure their CDN is configured to pull from the correct origin path.

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[coderabbitai]

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ℹ️ Recent review info

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Run ID: 600030c2-19d0-4889-a547-5639a71ab37a

📥 Commits

Reviewing files that changed from the base of the PR and between d5fca1c and 5aeb303.

📒 Files selected for processing (2)

• ghost/core/core/frontend/meta/asset-url.js
• ghost/core/test/unit/frontend/meta/asset-url.test.js

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Walkthrough

The getAssetUrl() function has been modified to support asset CDN configuration. When config.get('urls:assets') is available, it constructs an absolute base URL by trimming trailing slashes and appending a forward slash. If the configuration is absent, the function preserves previous behavior by using the subdirectory-relative base. Comprehensive test coverage has been added to validate URL construction for theme and public assets when the CDN base is configured, including edge cases for trailing slashes, cache-busting parameters, anchor fragments, and subdirectory handling.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding a urls:assets config option for serving static theme assets from a CDN.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, explaining the feature, its benefits, configuration, and behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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[sonarqubecloud]

Quality Gate failed

Failed conditions
3.3% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[muratcorlu]

I am not sure if I need to do anything about Sonar check, since it's mentioning repeating lines on test file, which is completely normal, I think.