diff --git a/services/clsi/app/js/QuartoRunner.js b/services/clsi/app/js/QuartoRunner.js
index 5a762656f0..4f2cc9cc57 100644
--- a/services/clsi/app/js/QuartoRunner.js
+++ b/services/clsi/app/js/QuartoRunner.js
@@ -168,15 +168,19 @@ function _pythonVenvPrep(venvBaseDir) {
     `if [ -n "$RHASH" ]; then ` +
     `VDIR="$VBASE/$RHASH"; mkdir -p "$VBASE" 2>/dev/null; ` +
     `( flock 9 || exit 0; ` +
-    `if [ ! -f "$VDIR/.verso-complete" ]; then ` +
+    `if [ ! -f "$VDIR/.verso-ready" ]; then ` +
     `echo "Installing Python packages from requirements.txt..."; rm -rf "$VDIR"; ` +
     `python3 -m venv --system-site-packages "$VDIR" ` +
     `&& "$VDIR/bin/pip" install --no-input --disable-pip-version-check -r requirements.txt ` +
-    `&& touch "$VDIR/.verso-complete" ` +
+    // Register a python3 kernelspec INSIDE the venv (argv -> the venv's python)
+    // so Quarto runs the kernel in the venv, not the base /usr/bin/python3 from
+    // the global kernelspec. ipykernel is visible via --system-site-packages.
+    `&& "$VDIR/bin/python3" -m ipykernel install --sys-prefix --name python3 --display-name "Python 3" ` +
+    `&& touch "$VDIR/.verso-ready" ` +
     `|| echo "ERROR: Failed to install Python packages from requirements.txt"; ` +
     `fi ` +
     `) 9>"$VBASE/.$RHASH.lock" 2>&1; ` +
-    `if [ -f "$VDIR/.verso-complete" ]; then export QUARTO_PYTHON="$VDIR/bin/python3"; fi; ` +
+    `if [ -f "$VDIR/.verso-ready" ]; then export QUARTO_PYTHON="$VDIR/bin/python3"; fi; ` +
     `fi; ` +
     `fi; `
   )