[Rules] Changelog: cf.worker.upstream_zone in Transform Rules and 4xx/5xx content fetching in Custom Errors

[nikitacano]

Summary

Transform Rules now support the cf.worker.upstream_zone field, letting you conditionally apply rules based on which zone sent Workers subrequest.
Custom Errors can now fetch and store fallback assets even if the origin returns a 4xx or 5xx status code.

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PR Change Summary

Enhanced Transform Rules with support for the cf.worker.upstream_zone field and improved Custom Errors functionality for handling 4xx/5xx status codes.

• Introduced support for cf.worker.upstream_zone in Transform Rules.
• Enabled Custom Errors to fetch fallback assets for 4xx/5xx responses.
• Updated documentation to clarify conditions for custom error page visibility.

Modified Files

• src/content/docs/rules/custom-errors/troubleshooting.mdx

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[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/assets/images/	@cloudflare/pm-changelogs, @cloudflare/pcx-technical-writing
/src/content/changelog/	@cloudflare/pm-changelogs, @cloudflare/pcx-cloudflare-one
/src/content/docs/rules/	@pedrosousa, @cloudflare/pcx-technical-writing

[github-actions]

Preview URL: https://0d74057f.preview.developers.cloudflare.com
Preview Branch URL: https://rules-june-changelog.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/changelog/2025-06-09-transform-rule-subrequest-matching/	https://rules-june-changelog.preview.developers.cloudflare.com/changelog/2025-06-09-transform-rule-subrequest-matching/
https://developers.cloudflare.com/changelog/2025-06-09-custom-errors-fetch-4xx-5xx-assets/	https://rules-june-changelog.preview.developers.cloudflare.com/changelog/2025-06-09-custom-errors-fetch-4xx-5xx-assets/
https://developers.cloudflare.com/rules/custom-errors/troubleshooting/	https://rules-june-changelog.preview.developers.cloudflare.com/rules/custom-errors/troubleshooting/