constructor2828-web/RestableDOS — reverse-engineered prompt

Build me a tiny experimental operating system called RestableDOS that boots in QEMU through GRUB, especially using BIOS mode since UEFI is noted as not working right now. I want it to be a simple 64 bit C based OS with a basic graphical desktop feel, a procedural background, mouse cursor support, draggable little windows, and a minimal shell or terminal for commands.

It should include the low level pieces needed to boot, enter long mode, draw to a high resolution framebuffer, scan PCI devices, have basic PS/2 mouse handling, and load a small read only root filesystem image. Please keep it simple and focused on actually building and running with make all and make run-bios.

Use the existing structure with kernel code, drivers, GUI, shell, boot files, tools, linker script, and Makefile. If anything is unclear, look up current OSDev and GRUB Multiboot2 docs online if you need to.