Function media_player_bus_name 

pub fn media_player_bus_name(package_id: &str) -> String

The MPRIS bus name of the media player a launched package publishes: org.mpris.MediaPlayer2.<package id>.

The toolkit’s media session requests this name for the package it runs as, and a sandbox’s session-bus filter lets the package own exactly this name and no other. Both name it here so the request and the grant cannot drift apart; a mismatch would have the bus refuse the player and leave it out of the desktop’s now-playing controls.