diff --git a/local/recipes/core/grub/grub.cfg b/local/recipes/core/grub/grub.cfg
index 5a547b7b..61508e9a 100644
--- a/local/recipes/core/grub/grub.cfg
+++ b/local/recipes/core/grub/grub.cfg
@@ -6,9 +6,9 @@
 # Place this file at EFI/BOOT/grub.cfg on the ESP.
 # The install-grub.sh script handles this automatically.
 #
-# To customize: edit this file before running install-grub.sh,
-# or modify the ESP directly with mtools:
-#   mcopy -i harddrive.img@@1048576 grub.cfg ::EFI/BOOT/grub.cfg
+# To customize: edit this file before building GRUB (make r.grub),
+# or modify the ESP directly with fat_tool.py:
+#   python3 local/scripts/fat_tool.py cp-in harddrive.img 1048576 grub.cfg EFI/BOOT/grub.cfg
 
 set default=0
 set timeout=5
diff --git a/local/recipes/core/grub/recipe.toml b/local/recipes/core/grub/recipe.toml
index 41c5f36c..d8ace826 100644
--- a/local/recipes/core/grub/recipe.toml
+++ b/local/recipes/core/grub/recipe.toml
@@ -26,12 +26,20 @@ script = """
 unset CC CXX CPP LD AR NM RANLIB OBJCOPY STRIP PKG_CONFIG
 unset CFLAGS CXXFLAGS CPPFLAGS LDFLAGS
 
+# Verify host tools are available before starting the build.
+for tool in gcc make bison flex; do
+    if ! command -v "${tool}" &>/dev/null; then
+        echo "ERROR: Required host tool '${tool}' not found" >&2
+        exit 1
+    fi
+done
+
 # Out-of-tree build (GRUB requires this for some configurations)
-mkdir -p "${COOKBOOK_BUILD}/grub-build"
-cd "${COOKBOOK_BUILD}/grub-build"
+mkdir -p "${COOKBOOK_BUILD}/grub-build" || exit 1
+cd "${COOKBOOK_BUILD}/grub-build" || exit 1
 
 # GRUB release tarballs miss extra_deps.lst (normally generated by autogen.sh)
-touch "${COOKBOOK_SOURCE}/grub-core/extra_deps.lst"
+touch "${COOKBOOK_SOURCE}/grub-core/extra_deps.lst" || exit 1
 
 # Configure for host, targeting x86_64 EFI platform output.
 # --target=x86_64 means "produce boot images for x86_64"
@@ -48,10 +56,10 @@ echo "Configuring GRUB for x86_64 EFI..."
     --disable-grub-mount \
     --disable-device-mapper \
     --disable-libzfs \
-    --prefix="${COOKBOOK_STAGE}/usr"
+    --prefix="${COOKBOOK_STAGE}/usr" || exit 1
 
 echo "Building GRUB..."
-make -j "${COOKBOOK_MAKE_JOBS}"
+make -j "${COOKBOOK_MAKE_JOBS}" || exit 1
 
 # Create output directory
 mkdir -p "${COOKBOOK_STAGE}/usr/lib/boot"
@@ -101,7 +109,7 @@ echo "Creating standalone GRUB EFI image..."
     ls \
     cat \
     halt \
-    reboot
+    reboot || exit 1
 
 # Verify output
 if [ ! -f "${COOKBOOK_STAGE}/usr/lib/boot/grub.efi" ]; then