Updates changelog.json with latest notes from 2025-10 release

[andguy95]

WHY are these changes introduced?

Closes https://github.com/Shopify/developer-tools-team/issues/988.

The 2025.10.0 release includes updates across two CI release PRs but was missing its changelog.json entry. Without this entry, the h2 upgrade command cannot detect version 2025.10.0 or provide migration guidance to developers.

WHAT is this pull request doing?

Adds a changelog entry for Hydrogen version
2025.10.0 to enable the h2 upgrade command to
detect and guide developers through this upgrade.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[shopify]

Oxygen deployed a preview of your an-changelogjson-for-2025-10 branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 5, 2026 5:16 PM

Learn more about Hydrogen's GitHub integration.

[kdaviduik]

some small comments but overall LGTM

[kdaviduik]

(threading)

also please double check this works by scaffolding by running h2 upgrade locally and using this changelog. I think there's a flag or something you can pass to use your local version (and patch-package is always an option too)

[andguy95]

Ran against the 2025.7.1 version locally. Looks to be good!

[kdaviduik]

LGTM!

[kdaviduik]

note: technically the React 19 support and the CA API change(s) were in 2025.7.3, but we never did an entry in here for that version (i think Gray started one at one point but it never got finished).

so right now this entry contains all the changes for 2025.7.3 + 2025.10.0. I think that's fine, i just wanted to make a note about it in case anyone (or our future selves) get confused :)