instrumented the thunk to print a letter per step so a hang names its own murderer. result: Rer, then nothing. R entered real mode, e entered the EDD read, r was about to issue a disk reset, ah=00h, the simplest int 13h call there is, no transfer, and it never returned. if even a no-op reset hangs after the PM excursion, the bios’s whole disk service is dead post-protected-mode on this machine, full stop. so the fix is a native usb driver. helix talks EHCI directly, bios for boot and native for runtime, as it should be, but that’s pci + ownership handoff from the very SMM that broke us + enumeration + BOT/scsi, and you don’t bring that up blind, one teletype letter per reboot, right before losing the hardware. deferred until the laptop’s back on hand; qemu remains unaffected.