chore: (DNM) test branch for box layout and resize + anchor observer primitives

[LFDanLu]

Closes

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices
• I understand every change in this PR and can explain why it's there.
• If AI-assisted, I followed our AI contribution guidance and pointed my assistant at CLAUDE.md.

📝 Test Instructions:

🧢 Your Project:

[nwidynski]

@LFDanLu Just as a note to be aware of, I would like to defer support for scroll-margin-box and scroll-padding-box into follow ups. I've found an issue with them, while working on Reids transform comment. To be more specific, a scroll action is always performed in a scroll containers coordinate space, meaning we need a ref to the container to support transforms on a scroll-margin-box target. Instead of adding another option, I would like to handle that with a super class instead. Just let me know once you are done with testing so I can remove these for now 👍

[LFDanLu]

@nwidynski thanks for the heads up! Feel free to remove them in your PR whenever and I can pull those in, we haven't done testing yet, need to reschedule it sometime this week due to the US holiday yesterday haha

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[nwidynski]

@LFDanLu Alright, done. I've also had Claude add some stories for your convenience, take these with a grain of salt. Also note that the "Animate transform" button of the anchor story only works in Chrome. This is expected behavior, since its the only engine currently supporting a feature called "Anchor follows transforms". Safari will catch up with 27 this month and Firefox will soon also. It is opt-out, without an additional CSS attribute, so it will just start working.

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

## API Changes

@react-aria/utils

/@react-aria/utils:getParentElement

+getParentElement {
+  node: Node
+  returnVal: undefined
+}

/@react-aria/utils:getParentNode

+getParentNode {
+  node: Node | Element | null | undefined
+  returnVal: undefined
+}

/@react-aria/utils:getPropagationTargets

+getPropagationTargets {
+  from: Element | null | undefined
+  to?: Document | Window | Element | null
+  returnVal: undefined
+}

---

[rspbot]

Agent Skills Changes

Modified (9)

• react-aria/agent-skills/index.json $\color{green}{+1}$ $\color{red}{-1}$
• react-aria/agent-skills/react-aria.tar.gz
• react-aria/agent-skills/react-aria/references/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/index.json $\color{green}{+3}$ $\color{red}{-3}$
• s2/agent-skills/migrate-react-spectrum-v3-to-s2.tar.gz
• s2/agent-skills/react-spectrum-s2.tar.gz
• s2/agent-skills/react-spectrum-s2/references/guides/ai-components.md $\color{red}{-17}$
• s2/agent-skills/react-spectrum-s2/references/react-aria/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/spectrum-audit.tar.gz

Install

React Spectrum S2:

npx skills add https://d1pzu54gtk2aed.cloudfront.net/pr/96b8856c2d069d33a49a91e4490f5625377a28a0/

React Aria:

npx skills add https://d5iwopk28bdhl.cloudfront.net/pr/96b8856c2d069d33a49a91e4490f5625377a28a0/