diff --git a/build-common.sh b/build-common.sh
index 0dfc202..1b93b76 100644
--- a/build-common.sh
+++ b/build-common.sh
@@ -131,7 +131,11 @@ cleanup_site_packages() {
     done
 
     # ── zeroconf ─────────────────────────────────────────────
-    rm -rf "$sp_dir/zeroconf/_services" 2>/dev/null || true
+    # DO NOT strip zeroconf/_services — the compiled Cython _listener.pyd
+    # imports from it, and the import fails at runtime with:
+    # ModuleNotFoundError: No module named 'zeroconf._services'
+    # Same class of bug as numpy — "presumed unused" submodule is actually
+    # imported internally by the package's own compiled code.
 
     # ── Strip debug symbols ──────────────────────────────────
     if command -v strip &>/dev/null; then
@@ -180,3 +184,57 @@ compile_and_strip_sources() {
     # __pycache__ dirs are redundant now that we have legacy .pyc files
     find "$target_dir" -type d -name __pycache__ -exec rm -rf {} + 2>/dev/null || true
 }
+
+# ── Import smoke test ────────────────────────────────────────
+#
+# Verifies that every top-level dependency that wled_controller actually
+# uses can be imported from the stripped site-packages. Catches regressions
+# where cleanup_site_packages removes a submodule that turns out to be
+# imported internally by the package (e.g. numpy.linalg, zeroconf._services).
+# Failing here is cheap; failing on a user's machine after install is not.
+#
+# Args:
+#   $1 — path to site-packages to test against
+#   $2 — python executable
+#   $3 — (optional) extra PYTHONPATH entry (e.g. app/src for wled_controller)
+
+smoke_test_imports() {
+    local sp_dir="$1"
+    local py_cmd="${2:-python3}"
+    local extra_path="${3:-}"
+
+    echo "  Running import smoke test..."
+    local pypath="$sp_dir"
+    if [ -n "$extra_path" ]; then
+        pypath="$extra_path:$sp_dir"
+    fi
+
+    # Modules that MUST import cleanly for the app to start.
+    # If you add a new top-level dependency, add it here.
+    PYTHONPATH="$pypath" "$py_cmd" -c "
+import sys
+modules = [
+    'numpy', 'numpy.linalg', 'numpy.lib', 'numpy.matrixlib',
+    'cv2',
+    'fastapi', 'uvicorn', 'starlette', 'pydantic',
+    'zeroconf',
+    'PIL', 'PIL.Image',
+    'yaml',
+]
+failed = []
+for mod in modules:
+    try:
+        __import__(mod)
+    except Exception as e:
+        failed.append(f'{mod}: {type(e).__name__}: {e}')
+if failed:
+    print('SMOKE TEST FAILED:', file=sys.stderr)
+    for f in failed:
+        print(f'  {f}', file=sys.stderr)
+    sys.exit(1)
+print('  Smoke test passed (imported', len(modules), 'modules)')
+" || {
+        echo "  ERROR: smoke test failed — site-packages is broken, aborting build"
+        return 1
+    }
+}
diff --git a/build-dist-windows.sh b/build-dist-windows.sh
index a6f83e5..2e77d29 100644
--- a/build-dist-windows.sh
+++ b/build-dist-windows.sh
@@ -279,6 +279,21 @@ find "$SITE_PACKAGES/winrt" -name "*.pyi" -delete 2>/dev/null || true
 # the generated .pyc will ImportError on the target.
 compile_and_strip_sources "$SITE_PACKAGES" "python"
 
+# Windows cross-build: host python can't load win_amd64 .pyd files, so
+# we can't `import numpy` for real. Instead, check that the submodules
+# known to be imported internally exist on disk — the same landmines that
+# cost users a broken v0.0.0.dev0 installer.
+echo "  Verifying required submodules exist after cleanup..."
+for required in \
+    "numpy/linalg" "numpy/lib" "numpy/matrixlib" "numpy/ma" \
+    "zeroconf/_services"; do
+    if [ ! -d "$SITE_PACKAGES/$required" ] && [ ! -f "$SITE_PACKAGES/$required.py" ] && [ ! -f "$SITE_PACKAGES/$required.pyc" ]; then
+        echo "  ERROR: $required missing from site-packages — cleanup_site_packages removed something required. Aborting."
+        exit 1
+    fi
+done
+echo "  All required submodules present."
+
 WHEEL_COUNT=$(ls "$WHEEL_DIR"/*.whl 2>/dev/null | wc -l)
 echo "  Installed $WHEEL_COUNT packages"
 
diff --git a/build-dist.sh b/build-dist.sh
index 7e77a80..b35101d 100644
--- a/build-dist.sh
+++ b/build-dist.sh
@@ -56,6 +56,9 @@ cleanup_site_packages "$SITE_PACKAGES" "so" "so"
 # Pre-compile and strip .py sources (must happen AFTER cleanup)
 compile_and_strip_sources "$SITE_PACKAGES" "python"
 
+# Fail loud if cleanup broke any required import
+smoke_test_imports "$SITE_PACKAGES" "python"
+
 # ── Build frontend ───────────────────────────────────────────
 
 echo "[4/7] Building frontend..."