[Hanan88]

Closes #10951.

Summary

Popovers in a secondary window can use the opener’s viewport for placement, stay in place when their own window resizes, or close when an unrelated element scrolls.

Use the overlay and trigger’s owning document and window for geometry, resize events, and scroll handling. Keep explicitly configured boundaries and continue dismissing when an ancestor of the trigger scrolls. Add browser regression tests for placement, resize, and scroll dismissal in a secondary document.

📝 Test Instructions

• The two new secondary-document cases reproduced the original failures in Chromium. The Chrome overlay and ComboBox browser suites passed locally (8 passed, 2 skipped).
• Formatting and lint checks passed for the changed files.
• The full local Jest run hit a locale resolution error on Windows. The SSR run hit timeouts in the Table suite.

Release impact

• Only changes docs, tests, CI, or development tools. Nothing shipped to users changes.
• Fixes a bug or improves existing code without changing how apps use it.
• Adds a feature or API while keeping existing usage working.
• May break existing usage or require changes in apps that use this code.

✅ PR Checklist

• I followed the contributing guide.
• I tested this change locally and included the results in Test Instructions, or explained why testing does not apply.
• I understand and can explain every change in this PR. If I used AI assistance, I followed the AI contribution guidance.

🧢 Your Project

Independent open-source contribution, prepared with Codex assistance.