Constant TEXT_SPARE_KEYCODES 

pub const TEXT_SPARE_KEYCODES: [u32; 14];

Keycodes every client types a character on, the seat’s overlay takes first: F13 to F24, then the JIS IntlRo and IntlYen keys, as selkies’ own overlay does. A Wayland client may read a key’s code as the physical key it names before the keysym the keymap gives, and Chromium drops a code naming no key it knows (every one past 255) and runs its browser, media and launcher keys as commands, so Computer-Use text bound from 0x120 never reached it. A text spare is taken only where the base leaves it unbound or bound to vendor keysyms alone, and not while selkies’ overlay holds it.