fix(jupyter): stop overriding JUPYTERLAB_DIR (assets not found)

JupyterLab 4 ships its prebuilt application assets (static/, schemas/,
staging/) inside the pip package and installs them to the system share
path (e.g. /usr/local/share/jupyter/lab). JUPYTERLAB_DIR points at that
assets directory — it is NOT a user settings/extensions dir.

Commit d085e58 ("Fix JupyterLab writable extension paths") redirected
JUPYTERLAB_DIR to an empty user-writable folder
($HC_WRITABLE_BASE/.local/share/jupyter/lab), which has no assets, so
JupyterLab died on every boot with:

JupyterLab application assets not found in
"/home/node/.huggingclaw-runtime/.local/share/jupyter/lab"
Please run `jlpm run build:core` then `jupyter lab build`
or use a different app directory

The settings/extensions persistence that d085e58 actually wanted is
already handled by JUPYTERLAB_SETTINGS_DIR / JUPYTERLAB_WORKSPACES_DIR /
JUPYTER_CONFIG_DIR / JUPYTER_DATA_DIR, which are all kept intact. Only
the JUPYTERLAB_DIR override was wrong.

Removed the override in all three export blocks, dropped it from the
pre-create mkdir (which would otherwise call mkdir with an empty arg),
and stopped creating the now-pointless empty lab/ dir.

start.sh

@@ -568,7 +568,7 @@ mkdir -p /home/node/.openclaw/memory
 mkdir -p /home/node/.openclaw/extensions
 mkdir -p /home/node/.openclaw/workspace
 mkdir -p "$HC_WRITABLE_BASE/.local/bin" "$HC_WRITABLE_BASE/.local/lib" "$HC_WRITABLE_BASE/.npm-global"
-mkdir -p "$HC_WRITABLE_BASE/.jupyter" "$HC_WRITABLE_BASE/.local/share/jupyter" "$HC_WRITABLE_BASE/.local/share/jupyter/runtime" "$HC_WRITABLE_BASE/.local/share/jupyter/lab"
+mkdir -p "$HC_WRITABLE_BASE/.jupyter" "$HC_WRITABLE_BASE/.local/share/jupyter" "$HC_WRITABLE_BASE/.local/share/jupyter/runtime"
 chmod 700 /home/node/.openclaw
 chmod 700 /home/node/.openclaw/credentials
 
@@ -640,7 +640,9 @@ export PIP_USER="${PIP_USER:-1}"
 export JUPYTER_CONFIG_DIR="${JUPYTER_CONFIG_DIR:-$HC_WRITABLE_BASE/.jupyter}"
 export JUPYTER_DATA_DIR="${JUPYTER_DATA_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter}"
 export JUPYTER_RUNTIME_DIR="${JUPYTER_RUNTIME_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/runtime}"
-export JUPYTERLAB_DIR="${JUPYTERLAB_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/lab}"
+# NOTE: JUPYTERLAB_DIR must stay unset — it is JupyterLab's prebuilt application
+# assets dir (shipped with the pip package), not a settings dir. Overriding it
+# (as d085e58 did) breaks the UI with "application assets not found".
 export JUPYTERLAB_SETTINGS_DIR="${JUPYTERLAB_SETTINGS_DIR:-$JUPYTER_CONFIG_DIR/lab/user-settings}"
 export JUPYTERLAB_WORKSPACES_DIR="${JUPYTERLAB_WORKSPACES_DIR:-$JUPYTER_CONFIG_DIR/lab/workspaces}"
 export JUPYTER_PREFER_ENV_PATH="${JUPYTER_PREFER_ENV_PATH:-0}"
@@ -1799,8 +1801,9 @@ start_jupyter_once() {
     fi
   fi
 
-  # Pre-create runtime directory
-  mkdir -p "$JUPYTER_ROOT_DIR/.jupyter" "$JUPYTER_CONFIG_DIR" "$JUPYTER_DATA_DIR" "$JUPYTER_RUNTIME_DIR" "$JUPYTERLAB_DIR" "$JUPYTERLAB_SETTINGS_DIR" "$JUPYTERLAB_WORKSPACES_DIR"
+  # Pre-create runtime directory. JUPYTERLAB_DIR is intentionally absent — it
+  # is the system prebuilt assets dir, owned by the package, not user-writable.
+  mkdir -p "$JUPYTER_ROOT_DIR/.jupyter" "$JUPYTER_CONFIG_DIR" "$JUPYTER_DATA_DIR" "$JUPYTER_RUNTIME_DIR" "$JUPYTERLAB_SETTINGS_DIR" "$JUPYTERLAB_WORKSPACES_DIR"
 
   echo "Terminal  : starting (root: $JUPYTER_ROOT_DIR)"
   JUPYTER_LOG_FILE="/tmp/jupyterlab.log"
@@ -1819,7 +1822,7 @@ start_jupyter_once() {
   export JUPYTER_CONFIG_DIR="${JUPYTER_CONFIG_DIR:-$HC_WRITABLE_BASE/.jupyter}"
   export JUPYTER_DATA_DIR="${JUPYTER_DATA_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter}"
   export JUPYTER_RUNTIME_DIR="${JUPYTER_RUNTIME_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/runtime}"
-  export JUPYTERLAB_DIR="${JUPYTERLAB_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/lab}"
+  # JUPYTERLAB_DIR intentionally unset — see top-level env block.
   export JUPYTERLAB_SETTINGS_DIR="${JUPYTERLAB_SETTINGS_DIR:-$JUPYTER_CONFIG_DIR/lab/user-settings}"
   export JUPYTERLAB_WORKSPACES_DIR="${JUPYTERLAB_WORKSPACES_DIR:-$JUPYTER_CONFIG_DIR/lab/workspaces}"
   export JUPYTER_PREFER_ENV_PATH="${JUPYTER_PREFER_ENV_PATH:-0}"
@@ -1914,7 +1917,7 @@ export PIP_USER="${PIP_USER:-1}"
 export JUPYTER_CONFIG_DIR="${JUPYTER_CONFIG_DIR:-$HC_WRITABLE_BASE/.jupyter}"
 export JUPYTER_DATA_DIR="${JUPYTER_DATA_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter}"
 export JUPYTER_RUNTIME_DIR="${JUPYTER_RUNTIME_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/runtime}"
-export JUPYTERLAB_DIR="${JUPYTERLAB_DIR:-$HC_WRITABLE_BASE/.local/share/jupyter/lab}"
+# Do NOT override JUPYTERLAB_DIR — see top-level env block for the reason.
 export JUPYTERLAB_SETTINGS_DIR="${JUPYTERLAB_SETTINGS_DIR:-$JUPYTER_CONFIG_DIR/lab/user-settings}"
 export JUPYTERLAB_WORKSPACES_DIR="${JUPYTERLAB_WORKSPACES_DIR:-$JUPYTER_CONFIG_DIR/lab/workspaces}"
 export JUPYTER_PREFER_ENV_PATH="${JUPYTER_PREFER_ENV_PATH:-0}"