install/58205: NetBSD-10 sysinst creates non bootable MBR install

[abs%absd.org@localhost]

>Number:         58205
>Category:       install
>Synopsis:       NetBSD-10 sysinst creates non bootable MBR install
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 27 18:10:00 +0000 2024
>Originator:     David Brownlee
>Release:        NetBSD 10.0
>Organization:
>Environment:
NetBSD 10.0
>Description:
Installing netbsd-10 onto a USB key and selecting MBR fails to boot on a ThinkPad T495. Installing 9.4 boots fine.

key was blanked (no GPT and first few MB written with zeros) before test

The failed boot shows a page with

" mem[0xc000-0x3fff 0x87000-0x89fff ..."

The T495 does not have separate "Boot USB with UEFI vs BIOS" options, so it is possible it could be trying to boot the 128MB EFI partition sysinst creates, but it is not clear how that differs from 9.4 
>How-To-Repeat:
Install NetBSD-10 using MBR onto a blank USB key & try to boot on at least a ThinkPad T495
>Fix:
Don't do that