diff --git a/Makefile b/Makefile
index b0ce61b..eff377f 100644
--- a/Makefile
+++ b/Makefile
@@ -102,8 +102,11 @@ inspect: $(ISO_FILE)
 	bd_info $(ISO_FILE)
 	bd_list_titles $(ISO_FILE) -a
 
-run: bootstrap $(ISO_FILE)
-	scripts/run-vlc.sh $(ISO_FILE)
+# Preview the menu straight from the BDMV folder. libbluray loads the BD-J Xlet
+# from a folder but not from a UDF .iso on this setup (see scripts/run-vlc.sh),
+# so `run` intentionally does not depend on the ISO.
+run: bootstrap $(JAR_FILE)
+	scripts/run-vlc.sh $(DISC_DIR)
 
 open: run
 
diff --git a/README.md b/README.md
index eecb3ed..f1c603f 100644
--- a/README.md
+++ b/README.md
@@ -29,13 +29,22 @@ The ISO is written to:
 build/adjustments.iso
 ```
 
-`make run` launches VLC through the Blu-ray access module, not as a generic
-media file:
+`make run` previews the disc by pointing VLC's Blu-ray access module at the
+`build/disc` BDMV **folder**, not the ISO:
 
 ```sh
-vlc bluray:///absolute/path/to/build/adjustments.iso
+vlc --bluray-menu bluray:///absolute/path/to/build/disc
 ```
 
+Why the folder and not the ISO: when libbluray opens a UDF `.iso`, its BD-J
+runtime must copy `BDMV/JAR/00000.jar` out of the image into a temp cache dir
+before the JVM can load it. On this setup that write is refused by libbluray's
+BD-J `SecurityManager`, so the Xlet class is never found and VLC silently falls
+back to playing the raw playlist with no menu. Reading the folder lets
+libbluray load the JAR directly, so the menu Xlet runs. The ISO is still the
+artifact you burn/distribute; real players read the JAR from the disc
+filesystem directly and are unaffected.
+
 The initial menu is a Java Xlet overlay with a few bonus-feature placeholders
 and a hidden menu stub. The actual generated video is a short ffmpeg SMPTE bars
 pattern with AC-3 audio, authored as playlist `00000`.
diff --git a/scripts/run-vlc.sh b/scripts/run-vlc.sh
index 085fb1b..e6f79e7 100755
--- a/scripts/run-vlc.sh
+++ b/scripts/run-vlc.sh
@@ -1,12 +1,28 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-ISO_PATH="${1:-build/adjustments.iso}"
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 MISE_BIN="${MISE_BIN:-$HOME/.local/bin/mise}"
 
-if [[ ! -f "$ISO_PATH" ]]; then
-  echo "Missing ISO: $ISO_PATH" >&2
+# Default to the on-disk BDMV folder, not the ISO.
+#
+# When libbluray opens a UDF *image* (.iso), its BD-J stack must first copy
+# BDMV/JAR/00000.jar out of the image into a temp cache dir. On this setup that
+# write is refused by libbluray's BD-J SecurityManager (usingUdf=true, no disc
+# root), so the JAR never mounts, the Xlet class is never found, and VLC falls
+# back to playing the raw playlist with no menu. Opening the *folder* lets
+# libbluray read the JAR directly, so the Xlet (menu) loads. Pass an explicit
+# path to override (folder or .iso).
+TARGET="${1:-$ROOT_DIR/build/disc}"
+
+if [[ -d "$TARGET" && ! -d "$TARGET/BDMV" ]]; then
+  echo "Not a BDMV folder (no BDMV/ inside): $TARGET" >&2
+  echo "Run: make" >&2
+  exit 1
+fi
+
+if [[ ! -e "$TARGET" ]]; then
+  echo "Missing disc target: $TARGET" >&2
   echo "Run: make" >&2
   exit 1
 fi
@@ -32,5 +48,9 @@ if [[ -d "$LOCAL_VLC_PLUGINS" ]]; then
   export VLC_PLUGIN_PATH="$LOCAL_VLC_PLUGINS:/usr/lib/vlc/plugins${VLC_PLUGIN_PATH:+:$VLC_PLUGIN_PATH}"
 fi
 
-ABS_ISO="$(cd "$(dirname "$ISO_PATH")" && pwd)/$(basename "$ISO_PATH")"
-exec vlc --reset-plugins-cache "bluray://$ABS_ISO"
+if [[ -d "$TARGET" ]]; then
+  ABS_TARGET="$(cd "$TARGET" && pwd)"
+else
+  ABS_TARGET="$(cd "$(dirname "$TARGET")" && pwd)/$(basename "$TARGET")"
+fi
+exec vlc --reset-plugins-cache --bluray-menu "bluray://$ABS_TARGET"