current ROM BAR (0x30): febc0000 
sizing readback       : ffff0001 
restored              : febc0000 

kernel-side proof (unseeded vga_pci_map_bios attempt):

bit0 of the readback is the ROM decode-enable bit (RW per PCI spec);
pci_alloc_map() (sys/bus/pci/pci.c:3933-3966) runs PCI_BAR_MEM(testval)
on exactly this value and rejects the SYS_RES_MEMORY request.