diff --git a/README.md b/README.md
index d7a91bf..8ff9927 100644
--- a/README.md
+++ b/README.md
@@ -58,6 +58,7 @@ scenario tests (portal, OTA apply, display + touch, watchdog).
 | `drivers/` | hardened hardware-facing drivers: HAL seams, test harnesses |
 | `kernel/` | forward-port provenance and bring-up records (`patches/` is canonical) |
 | `tools/` | `config-lint` (static memory-map gates) and dev tooling |
+| `build/vendor.manifest` | the third-party trees this platform builds against (LVGL, the vendor RV1106 SDK), pinned to exact commits; `build/fetch-vendor.sh` obtains and verifies them |
 | `docs/` | architecture, ADRs (`decisions/`), CI/CD |
 
 ## Architecture
diff --git a/build/fetch-vendor.sh b/build/fetch-vendor.sh
new file mode 100755
index 0000000..8392075
--- /dev/null
+++ b/build/fetch-vendor.sh
@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+# Obtain (or verify) the third-party trees pinned in build/vendor.manifest.
+#
+# These trees are shared between worktrees and are far too large to live in git
+# (the vendor SDK alone is 21 GB, and its host tools bake in absolute paths, so
+# it must sit at ONE stable path anyway). What belongs in git is the answer to
+# "which commit" -- that is the manifest, and this is the only thing that reads
+# it.
+#
+#   fetch-vendor.sh --check [DIR]     report each tree's state; non-zero if any
+#                                     is missing or off its pin  (default: check)
+#   fetch-vendor.sh --fetch [DIR]     clone what is missing, then check
+#
+# DIR defaults to $WARDEN_VENDOR_DIR, else the conventional shared location
+# alongside a flare-edge checkout. Nothing is ever moved or reset: a tree that
+# has drifted is REPORTED, because a local change to a vendor tree is usually
+# someone's debugging session, not something to silently throw away.
+set -uo pipefail
+
+HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+MANIFEST="$HERE/vendor.manifest"
+MODE="check"
+DIR=""
+
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --check) MODE="check"; shift ;;
+    --fetch) MODE="fetch"; shift ;;
+    -h|--help) sed -n '2,18p' "$0"; exit 0 ;;
+    *) DIR="$1"; shift ;;
+  esac
+done
+
+[ -r "$MANIFEST" ] || { echo "FATAL: no manifest at $MANIFEST" >&2; exit 1; }
+command -v git >/dev/null || { echo "FATAL: git not on PATH" >&2; exit 1; }
+
+if [ -z "$DIR" ]; then
+  DIR="${WARDEN_VENDOR_DIR:-$HOME/projects/scada/flare-edge}"
+fi
+
+# Where each tree conventionally lives. lvgl sits under ui/ because that is the
+# shared tree flare-edge worktrees symlink into (ui-src/lvgl).
+tree_path() {
+  case "$1" in
+    lvgl)         echo "$DIR/ui/lvgl" ;;
+    luckfox-pico) echo "$DIR/sdk" ;;
+    *)            echo "$DIR/$1" ;;
+  esac
+}
+
+rc=0
+while IFS=$'\t' read -r name url commit desc; do
+  case "$name" in ''|\#*) continue ;; esac
+  path="$(tree_path "$name")"
+
+  # -e, not -d: a git worktree or submodule has a .git FILE, and lvgl is
+  # checked out as one here.
+  if [ ! -e "$path/.git" ]; then
+    if [ "$MODE" = "fetch" ]; then
+      echo "== cloning $name -> $path"
+      mkdir -p "$(dirname "$path")"
+      git clone --quiet "$url" "$path" || { echo "  FAILED to clone $name" >&2; rc=1; continue; }
+      git -C "$path" checkout --quiet "$commit" || { echo "  FAILED to check out $commit" >&2; rc=1; continue; }
+    else
+      echo "MISSING  $name  ($path)"
+      rc=1
+      continue
+    fi
+  fi
+
+  have="$(git -C "$path" rev-parse HEAD 2>/dev/null)"
+  if [ "$have" = "$commit" ]; then
+    # Local changes are reported but are NOT a failure. The vendor SDK is
+    # expected to carry them: tools/build-firmware.sh applies our sdk-patches
+    # series into that tree as part of every build, so a clean luckfox-pico
+    # checkout is the unusual state, not the healthy one.
+    dirty=""
+    [ -n "$(git -C "$path" status --porcelain 2>/dev/null | head -1)" ] && dirty="  (locally modified)"
+    echo "OK       $name  ${commit:0:12}$dirty"
+  else
+    echo "DRIFTED  $name  want ${commit:0:12}  have ${have:0:12}  ($path)"
+    echo "         not reset automatically: check whether that is deliberate, then"
+    echo "         either 'git -C $path checkout $commit' or update the manifest."
+    rc=1
+  fi
+done < "$MANIFEST"
+
+exit "$rc"
diff --git a/build/vendor.manifest b/build/vendor.manifest
new file mode 100644
index 0000000..59a9694
--- /dev/null
+++ b/build/vendor.manifest
@@ -0,0 +1,19 @@
+# Third-party trees this platform is built against, pinned to an exact commit.
+#
+# WHY A PIN AND NOT A COPY. Between them these are ~21 GB; the vendor SDK alone
+# is 21 GB of build tree with absolute paths baked into its host tools. Copying
+# that into git would make every clone of this repo unusable and would still not
+# make the result reproducible. What makes a build reproducible is knowing
+# EXACTLY which tree was used, and that is a commit id -- the same reasoning
+# build/fetch-kernel-tarball.sh already applies to the kernel, where a sha256
+# pin stands in for vendoring 150 MB of tarball.
+#
+# So this file is the single place that answers "which LVGL, which vendor SDK",
+# and fetch-vendor.sh is the only thing that acts on it. A checkout that has
+# drifted off its pin is reported, never silently used.
+#
+# Format: name<TAB>url<TAB>commit<TAB>description
+# Blank lines and lines starting with '#' are ignored.
+
+lvgl	https://github.com/lvgl/lvgl.git	066d8db0b54819223357731f68961a90b3d785b4	LVGL v9.5.0-383-g066d8db0b: the UI toolkit warden-ui links against
+luckfox-pico	https://github.com/LuckfoxTECH/luckfox-pico.git	824b817f889c2cbff1d48fcdb18ab494a68f69d1	Vendor RV1106 SDK: buildroot userspace, U-Boot and the host packaging tools. Being replaced by this repo; still the source of the rootfs and the FIT/resource host tools.