Boot the T2 kernel the ISO says it boots

Every boot entry has named vmlinuz-linux-t2 since 0638855, but the file has
contained stock Arch. Verified against the shipped ISO:

  arch/boot/x86_64/vmlinuz-linux-t2:
    bzImage, version 7.1.5-arch1-1 (linux@archlinux)

while the mirror carries linux-t2-7.1.4-2. T2 MacBooks have been installing
with no keyboard or trackpad in the live environment.

Kernel packages ship nothing in /boot — only usr/lib/modules/<kver>/vmlinuz.
install_kernel() in /usr/share/libalpm/scripts/mkinitcpio sources
/etc/mkinitcpio.d/<pkgbase>.preset and copies THAT package's kernel to whatever
ALL_kver names, whenever is_kernelcopy() sees an unowned absolute path. Our file
was named linux.preset, so it overrode releng's copy of the same name and
pointed the STOCK kernel at the T2 filenames. linux-t2's own generated preset
writes those same two paths, and stock won.

c23e0e7 introduced it a week after 0638855 added T2 support, so the feature
worked for exactly seven days: before the preset existed, releng's linux.preset
kept the stock kernel on its own filenames and linux-t2's generated preset
produced the real thing.

The fix is the filename. releng's linux.preset takes over the stock kernel
again, which now writes /boot/vmlinuz-linux and initramfs-linux.img instead of
squatting on the T2 names — so the ISO grows by one kernel and one archiso
initramfs. That cost is not free and is worth revisiting: the stock kernel is
in the live root only because releng's broadcom-wl hard-depends on it, and
broadcom-wl is a prebuilt module for that kernel which cannot load on the T2
one we now boot. Dropping both is ~147MB and old Broadcom Macs lose live Wi-Fi.

Boot the ISO on a T2 Mac before trusting this; the version string is only
evidence that the right kernel ships, not that it works.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

configs/airootfs/etc/mkinitcpio.d/linux-t2.preset

@@ -0,0 +1,18 @@
+# mkinitcpio preset file for the 'linux-t2' package on archiso
+#
+# The filename is the pkgbase, and that is load-bearing. Kernel packages ship
+# nothing in /boot — they only install usr/lib/modules/<kver>/vmlinuz — so
+# mkinitcpio's alpm hook sources /etc/mkinitcpio.d/<pkgbase>.preset and copies
+# THAT package's kernel to whatever ALL_kver names (is_kernelcopy in
+# /usr/share/libalpm/scripts/mkinitcpio). Named linux.preset, this pointed the
+# stock kernel at the T2 filenames, so the ISO booted stock Arch while every
+# boot entry said linux-t2 and T2 Macs got no keyboard or trackpad.
+#
+# releng ships its own linux.preset for the stock kernel; leave it alone.
+
+PRESETS=('archiso')
+
+ALL_kver='/boot/vmlinuz-linux-t2'
+archiso_config='/etc/mkinitcpio.conf.d/archiso.conf'
+
+archiso_image="/boot/initramfs-linux-t2.img"

configs/airootfs/etc/mkinitcpio.d/linux.preset

@@ -1,9 +0,0 @@
-# mkinitcpio preset file for the 'linux' package on archiso
-
-PRESETS=('archiso')
-
-ALL_kver='/boot/vmlinuz-linux-t2'
-archiso_config='/etc/mkinitcpio.conf.d/archiso.conf'
-
-archiso_image="/boot/initramfs-linux-t2.img"
-

plans/aarch64-support.md

@@ -76,9 +76,9 @@ aarch64 has no BIOS — only UEFI. Drop the syslinux path entirely on ARM.
 
 The cleanest cut: keep one `grub.cfg` shared, strip the x86 shell/memtest fragments at build time when `OMARCHY_ARCH=aarch64`. Don't fork the file.
 
-### 6. mkinitcpio preset — `configs/airootfs/etc/mkinitcpio.d/linux.preset`
+### 6. mkinitcpio preset — `configs/airootfs/etc/mkinitcpio.d/linux-t2.preset`
 
-References `vmlinuz-linux-t2` and `initramfs-linux-t2.img` (lines 5, 8). For aarch64, swap to `vmlinuz-linux` / `initramfs-linux.img`. Generate the file at build time from a template, keyed on arch.
+Names `vmlinuz-linux-t2` and `initramfs-linux-t2.img`. The filename is the pkgbase and the alpm hook keys off it, so aarch64 does not rename this file — it simply does not ship it, and releng's own `linux.preset` covers the stock kernel. Drop `linux-t2` from `arch_packages` on aarch64 and the boot entries point at `vmlinuz-linux` / `initramfs-linux.img`.
 
 ### 7. Configurator — `configs/airootfs/root/configurator`
 
@@ -145,7 +145,7 @@ Code:
 - `configs/efiboot/loader/loader.conf` — per-arch default entry
 - `configs/efiboot/loader/entries/01-archiso-x86_64-linux.conf` — generate aarch64 sibling at build time
 - `configs/grub/grub.cfg`, `loopback.cfg` — strip x86-only fragments on aarch64
-- `configs/airootfs/etc/mkinitcpio.d/linux.preset` — template by arch (drop linux-t2 on aarch64)
+- `configs/airootfs/etc/mkinitcpio.d/linux-t2.preset` — omit on aarch64 (drop linux-t2 there; releng's linux.preset covers the stock kernel)
 - `configs/airootfs/root/configurator` — branch archinstall JSON mirror list on `uname -m`; optionally guard lspci T2 probe
 - `.github/workflows/nightly-build.yml` — matrix x86_64/aarch64