Offer OEM mode only when the bundled runtime supports it

The configurator now peeks into the offline mirror's runtime package for
omarchy-oem-setup before offering the OEM install mode, so an ISO built
against a pre-OEM runtime can't start an install doomed to fail at the
staging phase (which still hard-checks as the backstop). Blank disks with no
OEM choice to offer skip the mode picker entirely, like the pre-OEM flow.

Also keep the test harness QMP socket in /tmp — unix socket paths cap at
~108 bytes, which nested test-run directories can exceed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/omarchy-iso-test

@@ -101,7 +101,9 @@ HTTP_PID=""
 
 mkdir -p "$BASE_DIR" "$RUN_DIR"
 
-QMP_SOCK="$RUN_DIR/qmp.sock"
+# Unix socket paths are capped at ~108 bytes, which a run directory nested in
+# test-runs/<iso-name>/runs/<timestamp> can exceed. Keep the socket in /tmp.
+QMP_SOCK=$(mktemp -u "${TMPDIR:-/tmp}/omarchy-iso-test-qmp.XXXXXX.sock")
 PIDFILE="$RUN_DIR/qemu.pid"
 
 log() {

configs/airootfs/root/configurator

@@ -781,6 +781,24 @@ open_partition_tool() {
   sleep 1
 }
 
+# OEM mode needs the bundled runtime package to ship the first-boot setup
+# (omarchy-oem-setup); an ISO built against an older runtime must not offer a
+# mode whose install would fail at the staging phase. Peek into the offline
+# mirror's runtime package once; outside the ISO (dry runs) offer the mode.
+oem_supported() {
+  if [[ -z ${OEM_SUPPORTED:-} ]]; then
+    local mirror=/var/cache/omarchy/mirror/offline pkg
+    OEM_SUPPORTED=true
+    if [[ -d $mirror ]]; then
+      pkg=$(ls "$mirror/$OMARCHY_RUNTIME_PACKAGE"-[0-9]*.pkg.tar.zst 2>/dev/null | head -1)
+      if [[ -z $pkg ]] || ! tar -tf "$pkg" usr/bin/omarchy-oem-setup &>/dev/null; then
+        OEM_SUPPORTED=false
+      fi
+    fi
+  fi
+  [[ $OEM_SUPPORTED == true ]]
+}
+
 # If the disk has no partition table or no unallocated free space, the only
 # viable paths write the whole disk, so the free-space mode is not offered.
 requires_full_disk_install() {
@@ -814,7 +832,9 @@ install_mode_form() {
   fi
   # OEM: install the whole system now, defer user setup to the machine's
   # first boot — for machines built to be sold or handed on.
-  choices+=("OEM install (new owner creates their user on first boot)")
+  if oem_supported; then
+    choices+=("OEM install (new owner creates their user on first boot)")
+  fi
   choices+=("Choose a different disk")
 
   step "Let's select how to install Omarchy..."
@@ -871,7 +891,14 @@ select_installation() {
     else
       full_disk_only=false
     fi
-    install_mode_form
+
+    # A blank disk with no OEM choice to offer has exactly one viable mode;
+    # skip the picker like the pre-OEM flow did.
+    if $full_disk_only && ! oem_supported; then
+      install_mode="Full disk install"
+    else
+      install_mode_form
+    fi
 
     case "$install_mode" in
       "Full disk install")
@@ -880,6 +907,11 @@ select_installation() {
           install_target="full_disk"
           return 0
         fi
+        # When the picker was skipped there is no menu to fall back to;
+        # declining the overwrite means picking another disk, as before.
+        if $full_disk_only && ! oem_supported; then
+          disk_form
+        fi
         ;;
       "OEM install"*)
         oem_install=true