diff --git a/scripts/build_android.sh b/scripts/build_android.sh
index 417ff535..bdb535ba 100755
--- a/scripts/build_android.sh
+++ b/scripts/build_android.sh
@@ -202,8 +202,12 @@ pack_game_love() {
   # APK, so the mod manager's Delete can't remove it and it reappears every
   # launch.  Pokewalker ships as an importable .zip instead, which gives it
   # a real install/upgrade/delete lifecycle.
+  # libs/ carries the vendored FlexLove toolkit the launcher UI is built on
+  # (src/import/LauncherView.lua requires it at the top level, and RomImporter
+  # calls into that view from both update and draw), so an archive without it
+  # dies on the first frame with nothing left to fall back to.
   (cd "$ROOT" && zip -q -9 -r "$LOVE_FILE" \
-    main.lua conf.lua src data assets tools/save-editor \
+    main.lua conf.lua src libs data assets tools/save-editor \
     tools/rom_manifest.json tools/rom_manifest_blue.json \
     tools/rom_manifest_yellow.json \
     -x '*.DS_Store' -x '*/.git/*' -x '*/.DS_Store' \
@@ -220,6 +224,12 @@ pack_game_love() {
     || fail "game.love is missing the save editor (Edit on a save row would crash)"
   grep -qx "$YELLOW_MANIFEST_RELATIVE" <<< "$archive_entries" \
     || fail "game.love is missing the Yellow ROM import manifest"
+  # This gate exists because libs/ was added to scripts/build.sh's payload and
+  # to no other packager, so Android and iOS built an APK/IPA whose launcher
+  # threw on require("libs.flexlove.FlexLove") before drawing anything.  Source
+  # runs read libs/ off the working tree, so only a build can catch it.
+  grep -qx 'libs/flexlove/FlexLove.lua' <<< "$archive_entries" \
+    || fail "game.love is missing the FlexLove UI toolkit (launcher dies on frame 1)"
   say "game.love: $(du -h "$LOVE_FILE" | cut -f1) -> $LOVE_FILE"
 
   # This script packs its own game.love (it does not reuse build.sh's), so it
diff --git a/scripts/build_ios.sh b/scripts/build_ios.sh
index d3fc2d77..ddc6fb1b 100755
--- a/scripts/build_ios.sh
+++ b/scripts/build_ios.sh
@@ -315,9 +315,13 @@ pack_game_love() {
   # it reappears every launch.  Mods install as .zips at runtime instead
   # (launcher -> MODS -> Import mod .zip), the same lifecycle as every
   # other platform.
+  # libs/ carries the vendored FlexLove toolkit the launcher UI is built on
+  # (src/import/LauncherView.lua requires it at the top level, and RomImporter
+  # calls into that view from both update and draw), so an archive without it
+  # dies on the first frame with nothing left to fall back to.
   # shellcheck disable=SC2086  # MANIFESTS is a deliberate word list
   (cd "$ROOT" && zip -q -9 -r "$LOVE_FILE" \
-    main.lua conf.lua src data assets tools/save-editor \
+    main.lua conf.lua src libs data assets tools/save-editor \
     $MANIFESTS \
     -x '*.DS_Store' -x '*/.git/*' -x '*/.DS_Store' \
     -x 'data/generated/*' -x 'assets/generated/*')
@@ -333,10 +337,14 @@ pack_game_love() {
   # in 0.1.45 through 0.1.47: decodeManifest (src/import/RomImporter.lua) errors
   # outright when a version's manifest is absent, so Import ROM on Yellow died
   # in the built app while dev, which reads the source tree, stayed green.
+  # libs/flexlove/FlexLove.lua is on the list for the same reason: it was added
+  # to build.sh's payload and to no other packager, so the mobile builds shipped
+  # a launcher that threw before drawing its first frame.
   archive_entries="$(unzip -Z1 "$LOVE_FILE")"
   # shellcheck disable=SC2086  # MANIFESTS is a deliberate word list
   for required in src/update/Boot.lua tools/save-editor/App.lua \
                   tools/save-editor/Kit.lua tools/save-editor/panels/Party.lua \
+                  libs/flexlove/FlexLove.lua \
                   $MANIFESTS; do
     printf '%s\n' "$archive_entries" | grep -qx "$required" \
       || fail "game.love is missing $required"