diff --git a/wasm-port/docs/porting-steps-standalone.md b/wasm-port/docs/porting-steps-standalone.md
index 5fff336..cd0ba33 100644
--- a/wasm-port/docs/porting-steps-standalone.md
+++ b/wasm-port/docs/porting-steps-standalone.md
@@ -467,6 +467,12 @@ Current verified progress:
   `sincos.c`. These probes use the same `TP_FLAGS` as the standalone TP
   harness, including the existing `-fpermissive` boundary required by
   upstream enum conversions in `tp.c`.
+- `tools/verify_vendor_sync.sh` now validates the LinuxCNC source extraction
+  boundary before native probes run. It rejects duplicate manifest entries,
+  missing or extra vendored files, and byte-level drift between each manifest
+  file under `vendor/linuxcnc/` and the matching file under `../linuxcnc/`.
+  `tools/source-manifest.txt` was also de-duplicated so the manifest is a
+  single authoritative extraction list.
 
 ## Phase 4: Port INI Parsing Without Editing Upstream
 
diff --git a/wasm-port/tests/native/verify_native_probes.sh b/wasm-port/tests/native/verify_native_probes.sh
index d2babaf..a1ca5bd 100755
--- a/wasm-port/tests/native/verify_native_probes.sh
+++ b/wasm-port/tests/native/verify_native_probes.sh
@@ -9,6 +9,7 @@ GCODE_ERROR_FIXTURE_DIR="$ROOT_DIR/tests/fixtures/gcode_errors"
 CANON_ERROR_FIXTURE_DIR="$ROOT_DIR/tests/fixtures/canon_errors"
 NAMEDPARAM_INI_FIXTURE="$ROOT_DIR/tests/fixtures/ini/namedparams.ini"
 
+"$ROOT_DIR/tools/verify_vendor_sync.sh"
 "$ROOT_DIR/tools/build_native_probes.sh"
 
 check_exitcode() {
diff --git a/wasm-port/tools/source-manifest.txt b/wasm-port/tools/source-manifest.txt
index 8444b6c..c1e496c 100644
--- a/wasm-port/tools/source-manifest.txt
+++ b/wasm-port/tools/source-manifest.txt
@@ -115,5 +115,3 @@ src/emc/rs274ngc/interp_o_word.cc
 src/emc/rs274ngc/interp_convert.cc
 src/emc/rs274ngc/interp_cycles.cc
 src/emc/rs274ngc/interp_g7x.cc
-src/emc/rs274ngc/interp_check.cc
-src/emc/rs274ngc/interp_execute.cc
diff --git a/wasm-port/tools/verify_vendor_sync.sh b/wasm-port/tools/verify_vendor_sync.sh
new file mode 100755
index 0000000..da3a80c
--- /dev/null
+++ b/wasm-port/tools/verify_vendor_sync.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+UPSTREAM_DIR="$ROOT_DIR/../linuxcnc"
+VENDOR_DIR="$ROOT_DIR/vendor/linuxcnc"
+MANIFEST_FILE="$ROOT_DIR/tools/source-manifest.txt"
+
+if [[ ! -d "$UPSTREAM_DIR" ]]; then
+  echo "missing upstream directory: $UPSTREAM_DIR" >&2
+  exit 1
+fi
+
+if [[ ! -d "$VENDOR_DIR" ]]; then
+  echo "missing vendor directory: $VENDOR_DIR" >&2
+  exit 1
+fi
+
+if [[ ! -f "$MANIFEST_FILE" ]]; then
+  echo "missing manifest: $MANIFEST_FILE" >&2
+  exit 1
+fi
+
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+MANIFEST_CLEAN="$TMP_DIR/manifest.clean"
+MANIFEST_SORTED="$TMP_DIR/manifest.sorted"
+VENDOR_SORTED="$TMP_DIR/vendor.sorted"
+
+while IFS= read -r src_rel; do
+  [[ -z "$src_rel" ]] && continue
+  [[ "${src_rel:0:1}" == "#" ]] && continue
+
+  if [[ "$src_rel" = /* || "$src_rel" == *".."* ]]; then
+    echo "invalid manifest path: $src_rel" >&2
+    exit 1
+  fi
+
+  printf '%s\n' "$src_rel" >> "$MANIFEST_CLEAN"
+done < "$MANIFEST_FILE"
+
+if [[ ! -s "$MANIFEST_CLEAN" ]]; then
+  echo "empty manifest: $MANIFEST_FILE" >&2
+  exit 1
+fi
+
+sort "$MANIFEST_CLEAN" > "$MANIFEST_SORTED"
+
+if duplicate_entries="$(uniq -d "$MANIFEST_SORTED")" && [[ -n "$duplicate_entries" ]]; then
+  echo "duplicate manifest entries:" >&2
+  printf '%s\n' "$duplicate_entries" >&2
+  exit 1
+fi
+
+find "$VENDOR_DIR" -type f | sed "s#^$VENDOR_DIR/##" | sort > "$VENDOR_SORTED"
+
+if extra_vendor="$(comm -23 "$VENDOR_SORTED" "$MANIFEST_SORTED")" && [[ -n "$extra_vendor" ]]; then
+  echo "vendor files not listed in manifest:" >&2
+  printf '%s\n' "$extra_vendor" >&2
+  exit 1
+fi
+
+if missing_vendor="$(comm -13 "$VENDOR_SORTED" "$MANIFEST_SORTED")" && [[ -n "$missing_vendor" ]]; then
+  echo "manifest files missing from vendor:" >&2
+  printf '%s\n' "$missing_vendor" >&2
+  exit 1
+fi
+
+while IFS= read -r src_rel; do
+  upstream_file="$UPSTREAM_DIR/$src_rel"
+  vendor_file="$VENDOR_DIR/$src_rel"
+
+  if [[ ! -f "$upstream_file" ]]; then
+    echo "missing upstream file: $src_rel" >&2
+    exit 1
+  fi
+
+  if ! cmp -s "$upstream_file" "$vendor_file"; then
+    echo "vendor drift from upstream: $src_rel" >&2
+    exit 1
+  fi
+done < "$MANIFEST_SORTED"
+
+echo "vendor sync validation complete"