docs/ci: implement yay 13 SIGSEGV workaround and update docs

airootfs/root/customize_airootfs.sh

@@ -172,6 +172,36 @@ chmod 440 /etc/sudoers.d/99-ii-builder
 # so the tree must be owned by the account that runs it.
 chown -R "${BUILD_USER}:${BUILD_USER}" "${DOTS_REPO}"
 
+# yay 13 (libalpm via purego/dyalpm) can SIGSEGV in alpm_release() at exit,
+# *after* the transaction and its hooks completed (failed CI run: crash in
+# dyalpm handle.Release). end-4 sees exit 2 and aborts. This shim, put first
+# on PATH for the install-deps run only, turns a failed plain `yay -S <pkgs>`
+# into success when every target is installed afterwards (pacman -T); any
+# other failure keeps yay's exit code. It lives in /tmp and is removed after.
+YAY_SHIM_DIR="$(mktemp -d /tmp/ii-yay-shim.XXXXXX)"
+cat > "${YAY_SHIM_DIR}/yay" <<'EOF'
+#!/bin/bash
+"${YAY_SHIM_REAL:-/usr/bin/yay}" "$@"
+rc=$?
+(( rc == 0 )) && exit 0
+sync=0
+targets=()
+for a in "$@"; do
+  case "$a" in
+    -S|--sync) sync=1 ;;
+    -S*) exit "$rc" ;;  # -Ss/-Si/-Syu/...: not a plain install
+    -*) ;;
+    *) targets+=("$a") ;;
+  esac
+done
+if (( sync && ${#targets[@]} )) && pacman -T -- "${targets[@]}" >/dev/null; then
+  echo "[yay-shim] yay exited ${rc}, but all ${#targets[@]} targets are installed - continuing" >&2
+  exit 0
+fi
+exit "$rc"
+EOF
+chmod 755 "${YAY_SHIM_DIR}" "${YAY_SHIM_DIR}/yay"
+
 # -f: never prompt (ask=false); -s: skip "pacman -Syu";
 # --skip-plasmaintg: optional Firefox widget that pulls 410 pkgs / 526 MiB of
 #                    KDE packages onto a non-KDE system;
@@ -180,11 +210,14 @@ chown -R "${BUILD_USER}:${BUILD_USER}" "${DOTS_REPO}"
 # shellcheck disable=SC2024  # the redirect is meant for the child, not sudo
 if ! sudo -u "${BUILD_USER}" env HOME="/home/${BUILD_USER}" \
     GIT_TERMINAL_PROMPT=0 \
+    PATH="${YAY_SHIM_DIR}:/usr/local/sbin:/usr/local/bin:/usr/bin" \
     bash -c "cd ${DOTS_REPO} && ./setup install-deps -f -s --skip-plasmaintg" \
     < <(yes e); then
+  rm -rf "${YAY_SHIM_DIR}"
   echo "[customize] end-4 ./setup install-deps failed" >&2
   exit 1
 fi
+rm -rf "${YAY_SHIM_DIR}"
 
 # ── Harvest the packages install-deps just built into the in-image local repo ─
 # The live /etc/pacman.conf points [local-aur] at /opt/localrepo; without the