feat(installer): Add warn-only post-install update step

AGENTS.md

@@ -53,7 +53,7 @@ install them into the target without the network.
 | `pacman.conf` | Repos: cachyos → core → extra → multilib → chaotic-aur → local-aur |
 | `bootstrap_packages` | Minimal build-time packages (`base`, `arch-install-scripts`) |
 | `airootfs/root/customize_airootfs.sh` | Runs inside chroot during build: keyrings, skel dotfiles (incl. end4-pC), qsConfig patch, end-4 `install-deps`, package harvest, uv/font pre-warm |
-| `airootfs/root/.live-pacman.conf` | `/etc/pacman.conf` of the built image (adds `[local-aur]` = `file:///opt/localrepo`) |
+| `airootfs/root/.live-pacman.conf` | `/etc/pacman.conf` of the built image (adds `[local-aur]` = `file:///opt/localrepo`); also what pacstrap resolves the target from, so `[cachyos]` must stay ahead of `[core]` like in `pacman.conf` |
 | `airootfs/usr/local/bin/alvin-install` | Installer: partitions, pacstrap, LUKS (systemd initramfs **or** experimental unl0kr + optional TPM2 unlock), user (fish shell), git identity + GitHub SSH keys, login manager (none/greetd/sddm/gdm) + autologin, optional sshd (default on), end-4 dotfiles (`--skip-alldeps`), boot |
 | `localrepo/build-end4-deps.sh` | Non-interactive AUR builds for end-4 dependencies |
 | `localrepo/update.sh` | Regenerates localrepo DB, syncs names to packages.x86_64, syncs `airootfs/opt/localrepo/` |
@@ -74,7 +74,7 @@ The airootfs overlay ships it as `/usr/local/bin/alvin-install` (mode `0755` for
   locale, login manager, sshd, summary) then a fixed order of `install_*` steps
   (partition → LUKS → format/mount → pacstrap → fstab → repos → timezone → locale →
   hostname → network → sshd → user → git/SSH → end-4 dots → mkinitcpio → bootloader →
-  TPM/unl0kr → login manager → autologin → cleanup). Screens and install steps are
+  TPM/unl0kr → login manager → autologin → update (reflector + keyrings + `pacman -Syu`, warn-only) → cleanup). Screens and install steps are
   independent — edit one without
   touching the other. An `EXIT` trap unmounts `$TARGET` and closes `cryptroot` on any exit.
 - **Package list**: `install_pacstrap` builds the *installed* system's list from the medium's
@@ -113,6 +113,7 @@ whitespace.
 - **MicroTeX flags**: the image's `makepkg.conf` is CachyOS's (`-march=native -O3`, LTO). GCC 16.2 hit an internal compiler error (segfault) on MicroTeX's `gtkmm_main.cpp` with it (failed CI run 155; not reproducible locally), so `customize_airootfs.sh` patches end-4's `illogical-impulse-microtex-git` PKGBUILD to `options=(!lto)` + `-O2` (our `localrepo/end4-pkgbuilds/microtex-git` carries the same).
 - **CAP_SETFCAP on the runner**: without it pacstrap drops `security.capability` xattrs (newuidmap/newgidmap, snap-confine, dumpcap, kwin_wayland, ...) from the live ISO with only a warning. `build-iso.yaml` fails the job early if the runner lacks it — fix the runner, don't remove the check.
 - **yay SIGSEGV on exit**: yay 13 (libalpm via purego/`dyalpm`) can segfault in `alpm_release()` *after* a finished transaction (failed CI run at end-4's `illogical-impulse-kde` step), which aborted `install-deps`. `customize_airootfs.sh` puts a temporary `yay` shim first on the builder's `PATH`: a failed plain `yay -S <pkgs>` counts as success only if `pacman -T` confirms every target is installed (it logs `[yay-shim]`). Every other failure keeps yay's exit code.
+- **gvfs / dead `~/.gvfs`**: `install_end4_dots` replays end-4's gsettings writes via `dbus-run-session` as the target user. A session bus D-Bus-activates gvfsd → gvfsd-fuse mounts `~/.gvfs` and dies with the bus, leaving a dead FUSE mount that root can't stat, so the home's catch-all `chown -R` failed (`cannot access '/mnt/home/<user>/.gvfs': Permission denied`) and aborted the install before the bootloader. The replay therefore runs with `GIO_USE_VFS=local GVFS_DISABLE_FUSE=1`, and the function unmounts anything mounted under the home before that chown — keep both.
 - mono's `cert-sync` runs before `ca-certificates.crt` exists during pacstrap, so `customize_airootfs.sh` (live) and `install_pacstrap` (target) re-run it.
 - `/etc/skel/.zshrc` is owned by `grml-zsh-config`, so ours is staged as `airootfs/root/.zshrc-skel` and installed by `customize_airootfs.sh` after pacstrap — never add files under `airootfs/` at paths a package owns, or pacstrap aborts with "exists in filesystem".
 - `packages.x86_64` is sorted alphabetically. Keep it sorted when adding/removing entries.