diff --git a/ciss_live_builder.sh b/ciss_live_builder.sh
index 49a5fea..323ee2c 100644
--- a/ciss_live_builder.sh
+++ b/ciss_live_builder.sh
@@ -124,22 +124,28 @@ sleep 4
 printf "\e[95m🧪 %s starting ... \e[0m\n" "${BASH_SOURCE[0]}"
 declare -grx VAR_SETUP="true"
 
-### SECURING SECRETS ARTIFACTS.
-test ! -L "${VAR_TMP_SECRET}" || {
-  . ./var/global.var.sh
-  printf "\e[91m❌ Refusing symlink: '%s'! Bye... \e[0m\n" "${VAR_TMP_SECRET}" >&2
-  exit "${ERR_SECRETSSYM}"
-}
-find "${VAR_TMP_SECRET}" -type f -exec chmod 0400 {} +
-find "${VAR_TMP_SECRET}" -type f -exec chown root:root {} +
-
 ### SOURCING VARIABLES.
 [[ "${VAR_SETUP}" == true ]] && {
   source_guard "./var/color.var.sh"
   source_guard "./var/global.var.sh"
 }
 
-### SOURCING LIBRARIES.
+### SOURCE THE MINIMUM REQUIRED FOR EARLY EXIT CLEANUP COVERAGE.
+[[ "${VAR_SETUP}" == true ]] && {
+  source_guard "./lib/lib_secret_validation.sh"
+  source_guard "./lib/lib_build_directory.sh"
+  source_guard "./lib/lib_debug_sanitizer.sh"
+  source_guard "./lib/lib_clean_up.sh"
+  source_guard "./lib/lib_trap_on_err.sh"
+  source_guard "./lib/lib_trap_on_exit.sh"
+}
+
+trap 'trap_on_exit "$?" "${BASH_SOURCE[0]}" "${LINENO}" "${FUNCNAME[0]:-main}" "${BASH_COMMAND}"' EXIT
+
+### Validate the fixed tmpfs secret staging area without modifying operator-provided files.
+validate_secret_staging_area
+
+### SOURCING REMAINING LIBRARIES.
 [[ "${VAR_SETUP}" == true ]] && {
   source_guard "./lib/lib_arg_parser.sh"
   source_guard "./lib/lib_arg_priority_check.sh"
@@ -158,7 +164,6 @@ find "${VAR_TMP_SECRET}" -type f -exec chown root:root {} +
   source_guard "./lib/lib_ciss_upgrades_boot.sh"
   source_guard "./lib/lib_ciss_upgrades_build.sh"
   source_guard "./lib/lib_clean_screen.sh"
-  source_guard "./lib/lib_clean_up.sh"
   source_guard "./lib/lib_copy_integrity.sh"
   source_guard "./lib/lib_gnupg.sh"
   source_guard "./lib/lib_hardening_root_pw.sh"
@@ -174,12 +179,13 @@ find "${VAR_TMP_SECRET}" -type f -exec chown root:root {} +
   source_guard "./lib/lib_run_analysis.sh"
   source_guard "./lib/lib_sanitizer.sh"
   source_guard "./lib/lib_secureboot_profile.sh"
-  source_guard "./lib/lib_trap_on_err.sh"
-  source_guard "./lib/lib_trap_on_exit.sh"
   source_guard "./lib/lib_update_microcode.sh"
   source_guard "./lib/lib_usage.sh"
 }
 
+### Add ERR handling after all remaining libraries are available.
+trap 'trap_on_err  "$?" "${BASH_SOURCE[0]}" "${LINENO}" "${FUNCNAME[0]:-main}" "${BASH_COMMAND}"' ERR
+
 ### PRE-SCAN SECURE BOOT PROFILE FOR BUILD-HOST PACKAGE CHECKS.
 ### Formal validation still happens in arg_parser().
 for ((idx=0; idx<${#ARY_PARAM_ARRAY[@]}; idx++)); do
@@ -223,10 +229,6 @@ if ! ${VAR_HANDLER_AUTOBUILD}; then printf "XXX\nInitialization done ... \nXXX\n
 ### Updating Status of Dialog Gauge Bar.
 if ! ${VAR_HANDLER_AUTOBUILD}; then printf "XXX\nActivate traps ... \nXXX\n50\n" >&3; fi
 
-### Following the CISS Bash naming and ordering scheme:
-trap 'trap_on_exit "$?" "${BASH_SOURCE[0]}" "${LINENO}" "${FUNCNAME[0]:-main}" "${BASH_COMMAND}"' EXIT
-trap 'trap_on_err  "$?" "${BASH_SOURCE[0]}" "${LINENO}" "${FUNCNAME[0]:-main}" "${BASH_COMMAND}"' ERR
-
 ### Updating Status of Dialog Gauge Bar.
 if ! ${VAR_HANDLER_AUTOBUILD}; then printf "XXX\nSanitizing Arguments ... \nXXX\n75\n" >&3; fi
 arg_check "$@"
diff --git a/config/hooks/live/zzzz_ciss_crypt_squash.hook.binary b/config/hooks/live/zzzz_ciss_crypt_squash.hook.binary
index be5a0da..60ce34d 100644
--- a/config/hooks/live/zzzz_ciss_crypt_squash.hook.binary
+++ b/config/hooks/live/zzzz_ciss_crypt_squash.hook.binary
@@ -66,6 +66,49 @@ readonly -f preallocate
 declare ROOTFS="${VAR_HANDLER_BUILD_DIR}/binary/live/filesystem.squashfs"
 declare LUKSFS="${VAR_HANDLER_BUILD_DIR}/binary/live/ciss_rootfs.crypt"
 declare KEYFD=""
+declare LUKS_KEY_FILE=""
+declare LUKS_KEY_FILENAME="${VAR_LUKS_KEY:-luks.txt}"
+declare LUKS_KEY_LINK_COUNT=""
+declare LUKS_KEY_MODE=""
+declare LUKS_KEY_OWNER=""
+declare SECRET_ROOT_FS=""
+declare SECRET_ROOT_MODE=""
+declare SECRET_ROOT_OWNER=""
+
+if [[ -L "${VAR_TMP_SECRET}" || ! -d "${VAR_TMP_SECRET}" ]]; then
+  printf "\e[91m❌ Unsafe secret root rejected. \e[0m\n" >&2
+  exit 42
+fi
+
+SECRET_ROOT_OWNER="$(stat -c '%u' "${VAR_TMP_SECRET}")"
+SECRET_ROOT_MODE="$(stat -c '%a' "${VAR_TMP_SECRET}")"
+SECRET_ROOT_FS="$(stat -f -c '%T' "${VAR_TMP_SECRET}")"
+if [[ "${SECRET_ROOT_OWNER}" != "${EUID}" || "${SECRET_ROOT_MODE}" != "700" \
+  || ( "${SECRET_ROOT_FS}" != "tmpfs" && "${SECRET_ROOT_FS}" != "ramfs" ) ]]; then
+  printf "\e[91m❌ Unsafe secret-root ownership, permissions, or filesystem rejected. \e[0m\n" >&2
+  exit 42
+fi
+
+if [[ -z "${LUKS_KEY_FILENAME}" || "${LUKS_KEY_FILENAME}" == "." || "${LUKS_KEY_FILENAME}" == ".." \
+  || "${LUKS_KEY_FILENAME}" == */* || ! "${LUKS_KEY_FILENAME}" =~ ^[A-Za-z0-9._@%+=:,~-]+$ ]]; then
+  printf "\e[91m❌ Unsafe LUKS key filename rejected. \e[0m\n" >&2
+  exit 42
+fi
+
+LUKS_KEY_FILE="${VAR_TMP_SECRET}/${LUKS_KEY_FILENAME}"
+if [[ -L "${LUKS_KEY_FILE}" || ! -f "${LUKS_KEY_FILE}" ]]; then
+  printf "\e[91m❌ Unsafe LUKS key file rejected. \e[0m\n" >&2
+  exit 42
+fi
+
+LUKS_KEY_OWNER="$(stat -c '%u' "${LUKS_KEY_FILE}")"
+LUKS_KEY_MODE="$(stat -c '%a' "${LUKS_KEY_FILE}")"
+LUKS_KEY_LINK_COUNT="$(stat -c '%h' "${LUKS_KEY_FILE}")"
+if [[ "${LUKS_KEY_OWNER}" != "${EUID}" || "${LUKS_KEY_LINK_COUNT}" != "1" \
+  || ( "${LUKS_KEY_MODE}" != "400" && "${LUKS_KEY_MODE}" != "600" ) ]]; then
+  printf "\e[91m❌ Unsafe LUKS key ownership, permissions, or link count rejected. \e[0m\n" >&2
+  exit 42
+fi
 
 # shellcheck disable=SC2155
 declare -i VAR_ROOTFS_SIZE=$(stat -c%s -- "${ROOTFS}")
@@ -82,7 +125,7 @@ declare -i VAR_LUKSFS_SIZE=$(( ( (BASE_SIZE + ALIGN_BYTES - 1) / ALIGN_BYTES ) *
 
 preallocate "${LUKSFS}" "${VAR_LUKSFS_SIZE}"
 
-exec {KEYFD}<"${VAR_TMP_SECRET}/luks.txt"
+exec {KEYFD}<"${LUKS_KEY_FILE}"
 
 if [[ "${VAR_CDLB_INSIDE_RUNNER}" == "false" ]]; then
 
@@ -146,7 +189,7 @@ cryptsetup close crypt_liveiso
 
 exec {KEYFD}<&-
 
-shred -fzu -n 5 -- "${VAR_TMP_SECRET}/luks.txt"
+shred -fzu -n 5 -- "${LUKS_KEY_FILE}"
 
 rm -f -- "${ROOTFS}"
 
diff --git a/lib/lib_arg_parser.sh b/lib/lib_arg_parser.sh
index 680957c..82d26d4 100644
--- a/lib/lib_arg_parser.sh
+++ b/lib/lib_arg_parser.sh
@@ -57,20 +57,17 @@ guard_sourcing || return "${ERR_GUARD_SRCE}"
 #   None
 # Returns:
 #   ERR_ARG_MSMTCH: on failure
-#   ERR_ARG_MSMTCH: on failure
+#   ERR_BUILD_PATH: on failure
 #   ERR_CONTROL_CT: on failure
 #   ERR_DROPBEAR_V: on failure
-#   ERR_MISS_PWD_F: on failure
 #   ERR_MISS_PWD_P: on failure
-#   ERR_NOTABSPATH: on failure
-#   ERR_OWNS_PWD_F: on failure
 #   ERR_PASS_LENGH: on failure
 #   ERR_PASS_PLICY: on failure
 #   ERR_REIONICE_P: on failure
 #   ERR_REIO_C_VAL: on failure
 #   ERR_REIO_P_VAL: on failure
 #   ERR_RENICE_PRI: on failure
-#   ERR_RGHT_PWD_F: on failure
+#   ERR_SECRET_PATH: on failure
 #   ERR_SPLASH_PNG: on failure
 #   ERR__SOPS__VER: on failure
 #   ERR__SSH__PORT: on failure
@@ -134,12 +131,9 @@ arg_parser() {
           ;;
 
         --build-directory)
-          declare -gx VAR_HANDLER_BUILD_DIR="${2}"
-          if [[ ! "${VAR_HANDLER_BUILD_DIR}" =~ ^/ ]]; then
-            if ! ${VAR_HANDLER_AUTOBUILD}; then boot_screen_cleaner; fi
-            printf "\e[91m❌ Error: --build-directory MUST be an absolute path. Got: '%s'\n" "${VAR_HANDLER_BUILD_DIR}" >&2
-            exit "${ERR_NOTABSPATH}"
-          fi
+          declare build_directory="${2-}"
+          validate_build_directory_path "${build_directory}" build_directory || exit "${ERR_BUILD_PATH}"
+          declare -gx VAR_HANDLER_BUILD_DIR="${build_directory}"
           declare -gx VAR_BUILD_LOG="${VAR_HANDLER_BUILD_DIR}/cdlb_${VAR_ISO8601}_build.log"
           shift 2
           ;;
@@ -266,18 +260,22 @@ arg_parser() {
           ;;
 
         --key_age=*)
+          declare age_key="${1#*=}"
+          validate_secret_file_in_root "${age_key}" "SOPS Age key" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
           declare -gx VAR_AGE="true"
           # shellcheck disable=SC2034
-          declare -gx VAR_AGE_KEY="${1#*=}"
+          declare -gx VAR_AGE_KEY="${age_key}"
           shift 1
           ;;
 
         --key_luks=*)
+          declare luks_key="${1#*=}"
+          validate_secret_file_in_root "${luks_key}" "LUKS key file" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
           declare -gx VAR_LUKS="true"
           # shellcheck disable=SC2034
-          declare -gx VAR_LUKS_KEY="${1#*=}"
+          declare -gx VAR_LUKS_KEY="${luks_key}"
           shift 1
           ;;
 
@@ -473,39 +471,7 @@ arg_parser() {
 
           fi
 
-          if [[ ! -f "${pw_file}" ]]; then
-
-            if ! ${VAR_HANDLER_AUTOBUILD}; then boot_screen_cleaner; fi
-            printf "\e[91m❌ Error: --root-password-file password file '%s' does not exist.\e[0m\n" "${pw_file}" >&2
-            # shellcheck disable=SC2162
-            read -p  $'\e[92m✅ Press \'ENTER\' to exit the script ... \e[0m'
-            exit "${ERR_MISS_PWD_F}"
-
-          fi
-
-          declare owner
-          owner=$(stat -c '%U:%G' "${pw_file}")
-          if [[ "${owner}" != "root:root" ]]; then
-            chown root:root "${pw_file}" || {
-              if ! ${VAR_HANDLER_AUTOBUILD}; then boot_screen_cleaner; fi
-              printf "\e[91m❌ Error: --root-password-file failed to set owner root:root on '%s'.\e[0m\n" "${pw_file}" >&2
-              # shellcheck disable=SC2162
-              read -p  $'\e[92m✅ Press \'ENTER\' to exit the script ... \e[0m'
-              exit "${ERR_OWNS_PWD_F}"
-            }
-          fi
-
-          declare perms
-          perms=$(stat -c '%a' "${pw_file}")
-          if [[ "${perms}" -ne 400 ]]; then
-            chmod 0400 "${pw_file}" || {
-              if ! ${VAR_HANDLER_AUTOBUILD}; then boot_screen_cleaner; fi
-              printf "\e[91m❌ Error: --root-password-file failed to set permissions 0400 on '%s'.\e[0m\n" "${pw_file}" >&2
-              # shellcheck disable=SC2162
-              read -p  $'\e[92m✅ Press \'ENTER\' to exit the script ... \e[0m'
-              exit "${ERR_RGHT_PWD_F}"
-            }
-          fi
+          validate_secret_absolute_file "${pw_file}" "root password file" || exit "${ERR_SECRET_PATH}"
 
           declare plaintext_pw
           ### No tracing for security reasons ----------------------------------------------------------------------------------
@@ -558,6 +524,7 @@ arg_parser() {
           [[ "${VAR_EARLY_DEBUG}" == "true" ]] && set +x
 
           hash_temp=$(mkpasswd --method=sha-512 --salt="${salt}" --rounds=8388608 "${plaintext_pw}")
+          register_secret_value "${hash_temp}"
 
           ### Turn on tracing again --------------------------------------------------------------------------------------------
           [[ "${VAR_EARLY_DEBUG}" == "true" ]] && set -x
@@ -606,16 +573,20 @@ arg_parser() {
           ;;
 
         --signing_ca=*)
+          declare signing_ca="${1#*=}"
+          validate_secret_file_in_root "${signing_ca}" "signing CA file" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
-          declare -gx VAR_SIGNING_CA="${1#*=}"
+          declare -gx VAR_SIGNING_CA="${signing_ca}"
           shift 1
           ;;
 
         --signing_key=*)
+          declare signing_key="${1#*=}"
+          validate_secret_file_in_root "${signing_key}" "signing key file" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
           declare -gx VAR_SIGNER="true"
           # shellcheck disable=SC2034
-          declare -gx VAR_SIGNING_KEY="${1#*=}"
+          declare -gx VAR_SIGNING_KEY="${signing_key}"
           shift 1
           ;;
 
@@ -626,8 +597,10 @@ arg_parser() {
           ;;
 
         --signing_key_pass=*)
+          declare signing_key_pass="${1#*=}"
+          validate_secret_file_in_root "${signing_key_pass}" "signing passphrase file" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
-          declare -gx VAR_SIGNING_KEY_PASS="${1#*=}"
+          declare -gx VAR_SIGNING_KEY_PASS="${signing_key_pass}"
           shift 1
           ;;
 
@@ -694,8 +667,11 @@ arg_parser() {
           ;;
 
         --ssh-pubkey)
+          declare ssh_pubkey_dir="${2-}"
+          validate_secret_absolute_directory "${ssh_pubkey_dir}" "SSH public-key directory" || exit "${ERR_SECRET_PATH}"
+          validate_secret_file "${ssh_pubkey_dir}/authorized_keys" "SSH authorized_keys file" || exit "${ERR_SECRET_PATH}"
           # shellcheck disable=SC2034
-          declare -gx VAR_SSHPUBKEY="${2}"
+          declare -gx VAR_SSHPUBKEY="${ssh_pubkey_dir}"
           shift 2
           ;;
 
diff --git a/lib/lib_check_secrets.sh b/lib/lib_check_secrets.sh
index e82448d..c1c2c5c 100644
--- a/lib/lib_check_secrets.sh
+++ b/lib/lib_check_secrets.sh
@@ -23,36 +23,26 @@ guard_sourcing || return "${ERR_GUARD_SRCE}"
 #   0: on success
 #######################################
 x_remove() {
+  declare luks_key_filename="${VAR_LUKS_KEY:-luks.txt}" luks_key_path="" signing_pass_path=""
+  declare -a find_args=("${VAR_TMP_SECRET}" -xdev -type f)
+
   printf "\e[95m🧪 %s starting ... \e[0m\n" "${BASH_SOURCE[0]}"
 
-  declare _old_nullglob="" _old_dotglob=""
-
-  ### Enable nullglob/dotglob, disable failglob for safe globbing.
-  _old_nullglob="$(shopt -p nullglob || true)"
-  _old_dotglob="$( shopt -p dotglob  || true)"
-
-  shopt -s nullglob dotglob
+  validate_secret_staging_area || return "${ERR_SECRET_PATH}"
 
   if [[ "${VAR_SIGNER}" == "true" ]]; then
-
-    # shellcheck disable=SC2312
-    find "${VAR_TMP_SECRET}" -xdev -type f \
-      ! -path "${VAR_TMP_SECRET}/signing_key_pass.txt" \
-      ! -path "${VAR_TMP_SECRET}/luks.txt" \
-      -print0 \
-      | xargs -0 --no-run-if-empty shred -fzu -n 5 --
-
-  else
-
-    ### Removes secrets securely.
-    # shellcheck disable=SC2312
-    find "${VAR_TMP_SECRET}" -xdev -type f -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 --
-    find "${VAR_TMP_SECRET}" -xdev -depth -type d -empty -delete
-
+    validate_secret_file_in_root "${VAR_SIGNING_KEY_PASS}" "signing passphrase file" || return "${ERR_SECRET_PATH}"
+    signing_pass_path="${VAR_TMP_SECRET}/${VAR_SIGNING_KEY_PASS}"
+    find_args+=(! -path "${signing_pass_path}")
   fi
 
-  eval "${_old_nullglob}" 2>/dev/null || true
-  eval "${_old_dotglob}"  2>/dev/null || true
+  validate_secret_file_in_root "${luks_key_filename}" "LUKS key file" || return "${ERR_SECRET_PATH}"
+  luks_key_path="${VAR_TMP_SECRET}/${luks_key_filename}"
+  find_args+=(! -path "${luks_key_path}")
+
+  # shellcheck disable=SC2312
+  find "${find_args[@]}" -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 --
+  find "${VAR_TMP_SECRET}" -xdev -depth -type d -empty -delete
 
   printf "\e[92m✅ %s successfully applied. \e[0m\n" "${BASH_SOURCE[0]}"
 
diff --git a/lib/lib_clean_up.sh b/lib/lib_clean_up.sh
index 3075257..3bca5bb 100644
--- a/lib/lib_clean_up.sh
+++ b/lib/lib_clean_up.sh
@@ -32,15 +32,7 @@ guard_sourcing || return "${ERR_GUARD_SRCE}"
 #   0: on success
 #######################################
 clean_up() {
-  declare clean_exit_code="$1" fs_type="" _old_nullglob="" _old_dotglob="" _old_failglob=""
-
-  ### Enable nullglob/dotglob, disable failglob for safe globbing.
-  _old_nullglob="$(shopt -p nullglob || true)"
-  _old_dotglob="$( shopt -p dotglob  || true)"
-  _old_failglob="$(shopt -p failglob || true)"
-
-  shopt -s nullglob dotglob
-  shopt -u failglob
+  declare chroot_directory="" clean_exit_code="$1" fs_type="" includes_directory=""
 
   if [[ -e /dev/mapper/crypt_liveiso ]]; then
     cryptsetup close crypt_liveiso || true
@@ -52,10 +44,10 @@ clean_up() {
   rm -f -- "${VAR_NOTES}"
 
   ### Release advisory lock on FD 127.
-  flock -u 127
+  flock -u 127 2>/dev/null || true
 
   ### Close file descriptor 127.
-  exec 127>&-
+  exec 127>&- 2>/dev/null || true
 
   ### Remove the lockfile artifact.
   rm -f /run/lock/ciss_live_builder.lock
@@ -100,36 +92,41 @@ clean_up() {
   ### No tracing for security reasons ------------------------------------------------------------------------------------------
   [[ "${VAR_EARLY_DEBUG}" == "true" ]] && set +x
 
-  ### Removes secrets securely.
-  # shellcheck disable=SC2312
-  find "${VAR_TMP_SECRET}" -xdev -type f -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 --
-  find "${VAR_TMP_SECRET}" -xdev -depth -type d -empty -delete
-
-  ### Securely shred all regular files below ./includes.chroot, then remove empty dirs.
-  if [[ -d "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot" ]]; then
-
+  ### Removes secrets securely only after re-validating the fixed tmpfs staging area.
+  if validate_secret_staging_area "true"; then
     # shellcheck disable=SC2312
-    find "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot" -xdev -type f -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 --
-
-    ### Remove empty directories (bottom-up).
-    find "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot" -depth -xdev -type d -empty -delete
-
+    find "${VAR_TMP_SECRET}" -xdev -type f -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 -- || true
+    find "${VAR_TMP_SECRET}" -xdev -depth -type d -empty -delete || true
+  else
+    printf "\e[93m⚠ Secret cleanup skipped because the staging area failed validation. \e[0m\n" >&2
   fi
 
-  ### Delete all files and directories below ./chroot.
-  if [[ -d "${VAR_HANDLER_BUILD_DIR}/chroot" ]]; then
-
-    rm -rf "${VAR_HANDLER_BUILD_DIR}/chroot"
+  ### Destructive build cleanup requires the exact builder-owned directory marker.
+  if [[ -n "${VAR_HANDLER_BUILD_DIR}" ]] && validate_build_directory_marker "${VAR_HANDLER_BUILD_DIR}" "true"; then
+    if [[ -e "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot" || -L "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot" ]]; then
+      if validate_build_directory_subpath "${VAR_HANDLER_BUILD_DIR}" "config/includes.chroot" includes_directory "true"; then
+        # shellcheck disable=SC2312
+        find "${includes_directory}" -xdev -type f -print0 | xargs -0 --no-run-if-empty shred -fzu -n 5 -- || true
+        find "${includes_directory}" -depth -xdev -type d -empty -delete || true
+      else
+        printf "\e[93m⚠ Build includes cleanup skipped because the exact subpath failed validation. \e[0m\n" >&2
+      fi
+    fi
 
+    if [[ -e "${VAR_HANDLER_BUILD_DIR}/chroot" || -L "${VAR_HANDLER_BUILD_DIR}/chroot" ]]; then
+      if validate_build_directory_subpath "${VAR_HANDLER_BUILD_DIR}" "chroot" chroot_directory "true"; then
+        remove_build_paths "${chroot_directory}" || true
+      else
+        printf "\e[93m⚠ Build chroot cleanup skipped because the exact subpath failed validation. \e[0m\n" >&2
+      fi
+    fi
+  elif [[ -n "${VAR_HANDLER_BUILD_DIR}" ]]; then
+    printf "\e[93m⚠ Build-directory cleanup skipped because the exact builder-owned marker failed validation. \e[0m\n" >&2
   fi
 
   ### Turn on tracing again ----------------------------------------------------------------------------------------------------
   [[ "${VAR_EARLY_DEBUG}" == "true" ]] && set -x
 
-  eval "${_old_nullglob}" 2>/dev/null || true
-  eval "${_old_dotglob}"  2>/dev/null || true
-  eval "${_old_failglob}" 2>/dev/null || true
-
   return 0
 }
 ### Prevents accidental 'unset -f'.
diff --git a/lib/lib_gnupg.sh b/lib/lib_gnupg.sh
index 1737789..4fc07af 100644
--- a/lib/lib_gnupg.sh
+++ b/lib/lib_gnupg.sh
@@ -41,6 +41,12 @@ init_gnupg() {
 
   if [[ "${VAR_SIGNER}" == "true" ]]; then
 
+    validate_secret_file_in_root "${VAR_SIGNING_KEY}" "signing key file" || return "${ERR_SECRET_PATH}"
+    validate_secret_file_in_root "${VAR_SIGNING_KEY_PASS}" "signing passphrase file" || return "${ERR_SECRET_PATH}"
+    if [[ -n "${VAR_SIGNING_CA}" ]]; then
+      validate_secret_file_in_root "${VAR_SIGNING_CA}" "signing CA file" || return "${ERR_SECRET_PATH}"
+    fi
+
     __umask=$(umask)
     umask 0077
 
@@ -82,6 +88,7 @@ EOF
 
     declare __pw=""
     __pw="$(<"${VAR_SIGNING_KEY_PASSFILE}")"; __pw="${__pw%$'\r'}"; printf '%s' "${__pw}" >| "${VAR_SIGNING_KEY_PASSFILE}"
+    register_secret_value "${__pw}"
     __pw="" && unset __pw
 
     ### Turn on tracing again ----------------------------------------------------------------------------------------------------
diff --git a/lib/lib_hardening_ultra.sh b/lib/lib_hardening_ultra.sh
index 6b89183..ea80ef6 100644
--- a/lib/lib_hardening_ultra.sh
+++ b/lib/lib_hardening_ultra.sh
@@ -182,6 +182,8 @@ hardening_ultra() {
   printf "\e[95m🧪 Updating SSH Keys, Ports ... \e[0m\n"
 
   ### ./config/includes.chroot/root/.ssh ---------------------------------------------------------------------------------------
+  validate_secret_absolute_directory "${VAR_SSHPUBKEY}" "SSH public-key directory" || return "${ERR_SECRET_PATH}"
+  validate_secret_file "${VAR_SSHPUBKEY}/authorized_keys" "SSH authorized_keys file" || return "${ERR_SECRET_PATH}"
   install -d -m 0700 "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh"
   install -m 0600 -o root -g root "${VAR_SSHPUBKEY}/authorized_keys" "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh/"
 
diff --git a/lib/lib_lb_config_start.sh b/lib/lib_lb_config_start.sh
index d07f48e..246a521 100644
--- a/lib/lib_lb_config_start.sh
+++ b/lib/lib_lb_config_start.sh
@@ -23,36 +23,22 @@ guard_sourcing || return "${ERR_GUARD_SRCE}"
 #   0: on success
 #######################################
 lb_config_start() {
+  declare canonical_build_dir=""
+
   printf "\e[95m🧪 %s starting ... \e[0m\n" "${BASH_SOURCE[0]}"
 
-  if [[ ! -d ${VAR_HANDLER_BUILD_DIR} ]]; then
-
-    mkdir -p "${VAR_HANDLER_BUILD_DIR}"
-    # shellcheck disable=SC2164
-    cd "${VAR_HANDLER_BUILD_DIR}"
-    printf "\e[92m✅ '%s' created. \e[0m\n" "${VAR_HANDLER_BUILD_DIR}"
-
-  else
-
-    # shellcheck disable=SC2164
-    cd "${VAR_HANDLER_BUILD_DIR}"
-
-  fi
+  initialize_build_directory "${VAR_HANDLER_BUILD_DIR}" canonical_build_dir || return "${ERR_BUILD_PATH}"
+  VAR_HANDLER_BUILD_DIR="${canonical_build_dir}"
+  cd "${VAR_HANDLER_BUILD_DIR}" || return "${ERR_BUILD_PATH}"
 
   if [[ -d "${VAR_HANDLER_BUILD_DIR}/.build" ]]; then
 
-    # shellcheck disable=SC2164
-    cd "${VAR_HANDLER_BUILD_DIR}"
+    validate_build_directory_marker "${VAR_HANDLER_BUILD_DIR}" || return "${ERR_BUILD_PATH}"
 
     printf "\e[95m🧪 Deleting former config, binary and cache ... \e[0m\n"
 
     lb clean --binary --cache --purge --source
-
-    if [[ "${PWD}" == "${VAR_HANDLER_BUILD_DIR}" && "${PWD}" != "/" && -n "${PWD}" ]]; then
-
-      rm -rf -- ./* ./.??*
-
-    fi
+    clean_build_directory_contents "${VAR_HANDLER_BUILD_DIR}" || return "${ERR_BUILD_PATH}"
 
     printf "\e[92m✅ Deleting former config, binary and cache done.\e[0m\n"
 
diff --git a/lib/lib_primordial.sh b/lib/lib_primordial.sh
index 105ef4e..6db9116 100644
--- a/lib/lib_primordial.sh
+++ b/lib/lib_primordial.sh
@@ -84,6 +84,7 @@ init_primordial() {
   ### Check for SOPS AGE key integration ---------------------------------------------------------------------------------------
   if [[ "${VAR_AGE,,}" == "true" ]]; then
 
+    validate_secret_file_in_root "${VAR_AGE_KEY}" "SOPS Age key" || return "${ERR_SECRET_PATH}"
     install -d -m 0700                                 "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.config/sops/age"
     install -m 0400 "${VAR_TMP_SECRET}/${VAR_AGE_KEY}" "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.config/sops/age/keys.txt"
     shred -fzu -n 5 -- "${VAR_TMP_SECRET}/${VAR_AGE_KEY}" 2>/dev/null || rm -f "${VAR_TMP_SECRET}/${VAR_AGE_KEY}"
@@ -92,16 +93,35 @@ init_primordial() {
 
   ### Check for SSH CISS and PhysNet Primordial-Workflow™ integration -------------------------------------------------------
   if [[ "${VAR_SSHFP,,}" == "true" ]]; then
+    declare secret_key_file=""
+    declare -a identity_files=() host_key_files=()
+
+    validate_secret_directory "${VAR_TMP_SECRET}" "secret root" "true" || return "${ERR_SECRET_PATH}"
+
+    while IFS= read -r -d '' secret_key_file; do
+      validate_secret_file "${secret_key_file}" "primordial SSH identity file" || return "${ERR_SECRET_PATH}"
+      identity_files+=("${secret_key_file}")
+    done < <(find "${VAR_TMP_SECRET}" -maxdepth 1 -type f -name 'id*' -print0)
+
+    while IFS= read -r -d '' secret_key_file; do
+      validate_secret_file "${secret_key_file}" "primordial SSH host-key file" || return "${ERR_SECRET_PATH}"
+      host_key_files+=("${secret_key_file}")
+    done < <(find "${VAR_TMP_SECRET}" -maxdepth 1 -type f -name 'ssh_host_*' -print0)
+
+    (( ${#identity_files[@]} > 0 && ${#host_key_files[@]} > 0 )) || {
+      secret_validation_error "required primordial SSH key files are missing"
+      return "${ERR_SECRET_PATH}"
+    }
 
     install -d -m 0700                      "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh"
-    install -m 0600 "${VAR_TMP_SECRET}/id"* "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh/"
+    install -m 0600 "${identity_files[@]}"  "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh/"
     normalize_ssh_keys_in_dir               "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ssh"
-    shred -fzu -n 5 -- "${VAR_TMP_SECRET}/id"* 2>/dev/null || rm -f "${VAR_TMP_SECRET}/id"*
+    shred -fzu -n 5 -- "${identity_files[@]}" 2>/dev/null || rm -f "${identity_files[@]}"
 
     install -d -m 0700                             "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/ssh"
-    install -m 0600 "${VAR_TMP_SECRET}/ssh_host_"* "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/ssh/"
+    install -m 0600 "${host_key_files[@]}"         "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/ssh/"
     normalize_ssh_keys_in_dir                      "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/ssh/"
-    shred -fzu -n 5 -- "${VAR_TMP_SECRET}/ssh_host_"* 2>/dev/null || rm -f "${VAR_TMP_SECRET}/ssh_host_"*
+    shred -fzu -n 5 -- "${host_key_files[@]}" 2>/dev/null || rm -f "${host_key_files[@]}"
 
   fi
 
diff --git a/lib/lib_trap_on_exit.sh b/lib/lib_trap_on_exit.sh
index 14a6bce..c49e01e 100644
--- a/lib/lib_trap_on_exit.sh
+++ b/lib/lib_trap_on_exit.sh
@@ -49,8 +49,6 @@ trap_on_exit() {
 
     print_scr_exit "${errcode}"
 
-    exit "${errcode}"
-
   else
 
     if [[ "${ERRTRAP}" != "true" ]]; then
@@ -63,9 +61,16 @@ trap_on_exit() {
 
     fi
 
-    exit "${errcode}"
-
   fi
+
+  if ! sanitize_debug_logs; then
+    printf "\e[93m⚠ Final debug-log sanitisation failed; preserving original exit status %s. \e[0m\n" "${errcode}" >&2
+    if [[ -n "${LOG_ERROR:-}" && -f "${LOG_ERROR}" && ! -L "${LOG_ERROR}" ]]; then
+      printf "⚠ Final debug-log sanitisation failed; original exit status: %s.\n" "${errcode}" >> "${LOG_ERROR}" || true
+    fi
+  fi
+
+  exit "${errcode}"
 }
 ### Prevents accidental 'unset -f'.
 # shellcheck disable=SC2034