Constant KERNEL_CODE_SELECTOR 

const KERNEL_CODE_SELECTOR: SegmentSelector;

Kernel code segment selector for IDT entries.

At IDT init time the kernel runs under the UEFI firmware’s GDT (CS=0x38), but we intentionally use the kernel’s selector (0x08) so that once gdt::init() loads the real GDT the IDT entries are immediately valid.

Before gdt::init(), any exception will triple-fault because CS=0x08 references a non-existent descriptor in the UEFI GDT. That is acceptable: there should be no exceptions before the kernel GDT is live (the only known early #UD from init_serial / uart_16550 is already disabled).