[Bug] Missing sandbox_proxy.md in 1.9.x versioned docs

[zhangjaycee]

Bug Description

The sandbox_proxy.md user guide is present in version-1.8.x but missing from version-1.9.x versioned docs (both EN and zh-Hans).

sandbox_proxy.md was merged into 1.8.x on June 12 (commit cff897e), but when the 1.9.x version was created on June 18 (commit 1a30551), this file was not copied over.

• Present: docs/versioned_docs/version-1.8.x/User Guides/sandbox_proxy.md
• Present: docs/i18n/zh-Hans/docusaurus-plugin-content-docs/version-1.8.x/User Guides/sandbox_proxy.md
• Missing: docs/versioned_docs/version-1.9.x/User Guides/sandbox_proxy.md
• Missing: docs/i18n/zh-Hans/docusaurus-plugin-content-docs/version-1.9.x/User Guides/sandbox_proxy.md

Component Affected

• Documentation & Examples