Wrong "Unused CSS selector" in slotted content

[oub]

Describe the bug

CSS :has selector is incorrectly reported as unused in slotted content.

Reproduction

https://svelte.dev/playground/f4f152811664414b927a42289c904a52?version=5.18.0

Logs

System Info

System:                                              
    OS: Windows 11 10.0.22631                          
    CPU: (16) x64 13th Gen Intel(R) Core(TM) i5-1350P  
    Memory: 15.85 GB / 31.69 GB                        
  Binaries:                                            
    Node: 20.11.0 - C:\Program Files\nodejs\node.EXE   
    npm: 10.2.5 - C:\Program Files\nodejs\npm.CMD      
    pnpm: 9.15.2 - ~\AppData\Local\pnpm\pnpm.CMD       
  Browsers:                                            
    Internet Explorer: 11.0.22621.3527                 
  npmPackages:                                         
    svelte: ^5.18.0 => 5.18.0

Severity

blocking an upgrade

[dummdidumm]

Feels related to #14995, in that the :has logic seems to work only at the top level