Rapidweaver Classic +TotalCMS 3

I’m using RapidWeaver Classic on macOS Ventura 13.7.8, with PHP 8.4.4 selected in the project’s Advanced settings. I’m building a site with Weaver’s Space Total CMS 3.6.7. The published site works, but local Preview goes blank when the Total CMS Core stack is present.

A local PHP test showed that sys_get_temp_dir() returns /var/tmp/, but PHP cannot write there. It can write inside RapidWeaver’s generated Preview folder. Temporarily pointing Total CMS at that writable folder restored Preview. However, when I quit and reopened RapidWeaver, it regenerated the Preview files, overwrote the configuration change and the page went blank again.

Is there a supported way to set a writable temporary directory for RapidWeaver Classic’s local PHP preview server that persists across restarts?