chore: Update vscode task to kill previous instance (#2379)

.vscode/run-once.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Ensures only one instance of a command runs at a time. If a previous
+# instance is still running (e.g. orphaned after a VS Code crash), it is
+# killed before starting the new one.
+#
+# Kills the entire process tree (not just the stored PID) because `yarn`
+# spawns child processes (e.g. rollup/node) that hold the port. After
+# killing, waits for the port to be released before starting the new
+# instance.
+#
+# Usage: run-once.sh <pidfile> <port> <command...>
+
+set -euo pipefail
+
+PIDFILE="$1"; shift
+PORT="$1"; shift
+
+kill_tree() {
+  local pid="$1"
+  # Kill children first (depth-first), then the parent.
+  pkill -TERM -P "$pid" 2>/dev/null || true
+  kill "$pid" 2>/dev/null || true
+  tail --pid="$pid" -f /dev/null 2>/dev/null || true
+}
+
+wait_for_port() {
+  local port="$1"
+  local attempts=0
+  while ss -tlnp | grep -q ":${port} " && [ $attempts -lt 30 ]; do
+    sleep 0.2
+    attempts=$((attempts + 1))
+  done
+}
+
+if [ -f "$PIDFILE" ]; then
+  OLD_PID=$(cat "$PIDFILE" 2>/dev/null || true)
+  if [ -n "$OLD_PID" ] && kill -0 "$OLD_PID" 2>/dev/null; then
+    kill_tree "$OLD_PID"
+  fi
+  rm -f "$PIDFILE"
+  wait_for_port "$PORT"
+fi
+
+trap 'rm -f "$PIDFILE"' EXIT
+echo $$ > "$PIDFILE"
+exec "$@"