diff --git a/iso/builder/build.sh b/iso/builder/build.sh
index 072d11a..c180a29 100755
--- a/iso/builder/build.sh
+++ b/iso/builder/build.sh
@@ -111,63 +111,192 @@ resolve_iso_version() {
     resolve_audit_version
 }
 
+dump_memtest_debug() {
+    phase="$1"
+    lb_dir="${2:-}"
+    iso_path="${3:-}"
+    phase_slug="$(printf '%s' "${phase}" | tr ' /' '__')"
+    memtest_log="${LOG_DIR:-}/memtest-${phase_slug}.log"
+
+    (
+        echo "=== memtest debug: ${phase} ==="
+
+        echo "-- auto/config --"
+        if [ -f "${BUILDER_DIR}/auto/config" ]; then
+            grep -n -- '--memtest' "${BUILDER_DIR}/auto/config" || echo "  (no --memtest line found)"
+        else
+            echo "  (missing ${BUILDER_DIR}/auto/config)"
+        fi
+
+        echo "-- source bootloader templates --"
+        for cfg in \
+            "${BUILDER_DIR}/config/bootloaders/grub-pc/grub.cfg" \
+            "${BUILDER_DIR}/config/bootloaders/isolinux/live.cfg.in"; do
+            if [ -f "$cfg" ]; then
+                echo "  file: $cfg"
+                grep -n 'Memory Test\|memtest' "$cfg" || echo "    (no memtest lines)"
+            fi
+        done
+
+        if [ -n "$lb_dir" ] && [ -d "$lb_dir" ]; then
+            echo "-- live-build workdir package lists --"
+            for pkg in \
+                "$lb_dir/config/package-lists/bee.list.chroot" \
+                "$lb_dir/config/package-lists/bee-gpu.list.chroot" \
+                "$lb_dir/config/package-lists/bee-nvidia.list.chroot"; do
+                if [ -f "$pkg" ]; then
+                    echo "  file: $pkg"
+                    grep -n 'memtest' "$pkg" || echo "    (no memtest lines)"
+                fi
+            done
+
+            echo "-- live-build chroot/boot --"
+            if [ -d "$lb_dir/chroot/boot" ]; then
+                find "$lb_dir/chroot/boot" -maxdepth 1 -name 'memtest*' -print | sed 's/^/  /' || true
+            else
+                echo "  (missing $lb_dir/chroot/boot)"
+            fi
+
+            echo "-- live-build binary/boot --"
+            if [ -d "$lb_dir/binary/boot" ]; then
+                find "$lb_dir/binary/boot" -maxdepth 1 -name 'memtest*' -print | sed 's/^/  /' || true
+            else
+                echo "  (missing $lb_dir/binary/boot)"
+            fi
+
+            echo "-- live-build package cache --"
+            if [ -d "$lb_dir/cache/packages.chroot" ]; then
+                find "$lb_dir/cache/packages.chroot" -maxdepth 1 -name 'memtest86+*.deb' -print | sed 's/^/  /' || true
+            else
+                echo "  (missing $lb_dir/cache/packages.chroot)"
+            fi
+        fi
+
+        if [ -n "$iso_path" ] && [ -f "$iso_path" ]; then
+            echo "-- ISO memtest files --"
+            bsdtar -tf "$iso_path" | grep 'memtest' | sed 's/^/  /' || echo "  (no memtest files in ISO)"
+
+            echo "-- ISO GRUB memtest lines --"
+            bsdtar -xOf "$iso_path" boot/grub/grub.cfg 2>/dev/null | grep -n 'Memory Test\|memtest' || echo "  (no memtest lines in boot/grub/grub.cfg)"
+
+            echo "-- ISO isolinux memtest lines --"
+            bsdtar -xOf "$iso_path" isolinux/live.cfg 2>/dev/null | grep -n 'Memory Test\|memtest' || echo "  (no memtest lines in isolinux/live.cfg)"
+        fi
+
+        echo "=== end memtest debug: ${phase} ==="
+    ) | {
+        if [ -n "${LOG_DIR:-}" ] && [ -d "${LOG_DIR}" ]; then
+            tee "${memtest_log}"
+        else
+            cat
+        fi
+    }
+}
+
+memtest_fail() {
+    msg="$1"
+    iso_path="${2:-}"
+    echo "ERROR: ${msg}" >&2
+    dump_memtest_debug "failure" "${LB_DIR:-}" "$iso_path" >&2
+    exit 1
+}
+
 validate_iso_memtest() {
     iso_path="$1"
     echo "=== validating memtest in ISO ==="
 
-    [ -f "$iso_path" ] || { echo "ERROR: ISO not found for validation: $iso_path" >&2; exit 1; }
-    command -v bsdtar >/dev/null 2>&1 || { echo "ERROR: bsdtar is required for ISO validation" >&2; exit 1; }
+    [ -f "$iso_path" ] || memtest_fail "ISO not found for validation: $iso_path" "$iso_path"
+    command -v bsdtar >/dev/null 2>&1 || memtest_fail "bsdtar is required for ISO validation" "$iso_path"
 
     bsdtar -tf "$iso_path" | grep -q '^boot/memtest86+x64\.bin$' || {
-        echo "ERROR: memtest BIOS binary missing in ISO: boot/memtest86+x64.bin" >&2
-        exit 1
+        memtest_fail "memtest BIOS binary missing in ISO: boot/memtest86+x64.bin" "$iso_path"
     }
     bsdtar -tf "$iso_path" | grep -q '^boot/memtest86+x64\.efi$' || {
-        echo "ERROR: memtest EFI binary missing in ISO: boot/memtest86+x64.efi" >&2
-        exit 1
+        memtest_fail "memtest EFI binary missing in ISO: boot/memtest86+x64.efi" "$iso_path"
     }
 
     grub_cfg="$(mktemp)"
     isolinux_cfg="$(mktemp)"
-    trap 'rm -f "$grub_cfg" "$isolinux_cfg"' EXIT INT TERM
 
-    bsdtar -xOf "$iso_path" boot/grub/grub.cfg > "$grub_cfg" || {
-        echo "ERROR: failed to extract boot/grub/grub.cfg from ISO" >&2
-        exit 1
-    }
-    bsdtar -xOf "$iso_path" isolinux/live.cfg > "$isolinux_cfg" || {
-        echo "ERROR: failed to extract isolinux/live.cfg from ISO" >&2
-        exit 1
-    }
+    bsdtar -xOf "$iso_path" boot/grub/grub.cfg > "$grub_cfg" || memtest_fail "failed to extract boot/grub/grub.cfg from ISO" "$iso_path"
+    bsdtar -xOf "$iso_path" isolinux/live.cfg > "$isolinux_cfg" || memtest_fail "failed to extract isolinux/live.cfg from ISO" "$iso_path"
 
     grep -q 'Memory Test (memtest86+)' "$grub_cfg" || {
-        echo "ERROR: GRUB menu entry for memtest is missing" >&2
-        exit 1
+        memtest_fail "GRUB menu entry for memtest is missing" "$iso_path"
     }
     grep -q '/boot/memtest86+x64\.efi' "$grub_cfg" || {
-        echo "ERROR: GRUB memtest EFI path is missing" >&2
-        exit 1
+        memtest_fail "GRUB memtest EFI path is missing" "$iso_path"
     }
     grep -q '/boot/memtest86+x64\.bin' "$grub_cfg" || {
-        echo "ERROR: GRUB memtest BIOS path is missing" >&2
-        exit 1
+        memtest_fail "GRUB memtest BIOS path is missing" "$iso_path"
     }
     grep -q 'Memory Test (memtest86+)' "$isolinux_cfg" || {
-        echo "ERROR: isolinux menu entry for memtest is missing" >&2
-        exit 1
+        memtest_fail "isolinux menu entry for memtest is missing" "$iso_path"
     }
     grep -q '/boot/memtest86+x64\.bin' "$isolinux_cfg" || {
-        echo "ERROR: isolinux memtest path is missing" >&2
-        exit 1
+        memtest_fail "isolinux memtest path is missing" "$iso_path"
     }
 
     rm -f "$grub_cfg" "$isolinux_cfg"
-    trap - EXIT INT TERM
     echo "=== memtest validation OK ==="
 }
 
 AUDIT_VERSION_EFFECTIVE="$(resolve_audit_version)"
 ISO_VERSION_EFFECTIVE="$(resolve_iso_version)"
+ISO_BASENAME="easy-bee-${BEE_GPU_VENDOR}-v${ISO_VERSION_EFFECTIVE}-amd64"
+LOG_DIR="${DIST_DIR}/${ISO_BASENAME}.logs"
+LOG_ARCHIVE="${DIST_DIR}/${ISO_BASENAME}.logs.tar.gz"
+ISO_OUT="${DIST_DIR}/${ISO_BASENAME}.iso"
+LOG_OUT="${LOG_DIR}/build.log"
+
+cleanup_build_log() {
+    status="${1:-$?}"
+    trap - EXIT INT TERM HUP
+
+    if [ "${BUILD_LOG_ACTIVE:-0}" = "1" ]; then
+        BUILD_LOG_ACTIVE=0
+        exec 1>&3 2>&4
+        exec 3>&- 4>&-
+        if [ -n "${BUILD_TEE_PID:-}" ]; then
+            wait "${BUILD_TEE_PID}" 2>/dev/null || true
+        fi
+        rm -f "${BUILD_LOG_PIPE}"
+    fi
+
+    if [ -n "${LOG_DIR:-}" ] && [ -d "${LOG_DIR}" ] && command -v tar >/dev/null 2>&1; then
+        rm -f "${LOG_ARCHIVE}"
+        tar -czf "${LOG_ARCHIVE}" -C "${DIST_DIR}" "$(basename "${LOG_DIR}")" 2>/dev/null || true
+    fi
+
+    exit "${status}"
+}
+
+start_build_log() {
+    command -v tee >/dev/null 2>&1 || {
+        echo "ERROR: tee is required for build logging" >&2
+        exit 1
+    }
+
+    rm -rf "${LOG_DIR}"
+    rm -f "${LOG_ARCHIVE}"
+    mkdir -p "${LOG_DIR}"
+    BUILD_LOG_PIPE="$(mktemp -u "${TMPDIR:-/tmp}/bee-build-log.XXXXXX")"
+    mkfifo "${BUILD_LOG_PIPE}"
+
+    exec 3>&1 4>&2
+    tee "${LOG_OUT}" < "${BUILD_LOG_PIPE}" &
+    BUILD_TEE_PID=$!
+    exec > "${BUILD_LOG_PIPE}" 2>&1
+    BUILD_LOG_ACTIVE=1
+
+    trap 'cleanup_build_log "$?"' EXIT INT TERM HUP
+
+    echo "=== build log dir: ${LOG_DIR} ==="
+    echo "=== build log: ${LOG_OUT} ==="
+    echo "=== build log archive: ${LOG_ARCHIVE} ==="
+}
+
+start_build_log
 
 # Auto-detect kernel ABI: refresh apt index, then query current linux-image-amd64 dependency.
 # If headers for the detected ABI are not yet installed (kernel updated since image build),
@@ -564,6 +693,7 @@ export BEE_GPU_VENDOR_UPPER
 cd "${LB_DIR}"
 lb clean 2>&1 | tail -3
 lb config 2>&1 | tail -5
+dump_memtest_debug "pre-build" "${LB_DIR}"
 lb build 2>&1
 
 # --- persist deb package cache back to shared location ---
@@ -575,8 +705,8 @@ fi
 
 # live-build outputs live-image-amd64.hybrid.iso in LB_DIR
 ISO_RAW="${LB_DIR}/live-image-amd64.hybrid.iso"
-ISO_OUT="${DIST_DIR}/easy-bee-${BEE_GPU_VENDOR}-v${ISO_VERSION_EFFECTIVE}-amd64.iso"
 if [ -f "$ISO_RAW" ]; then
+    dump_memtest_debug "post-build" "${LB_DIR}" "$ISO_RAW"
     validate_iso_memtest "$ISO_RAW"
     cp "$ISO_RAW" "$ISO_OUT"
     echo ""