y-kubeconfig-import: set -u and guard unset reads; document current-context flip

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: solsson

bin/y-kubeconfig-import

@@ -1,17 +1,19 @@
 #!/usr/bin/env bash
-[ -z "$DEBUG" ] || set -x
-set -eo pipefail
+[ -z "${DEBUG:-}" ] || set -x
+set -euo pipefail
 
-[ -z "$1" ] && echo "First arg should be the path to a _temporary_ kubeconfig file" && exit 1
+[ -z "${1:-}" ] && echo "First arg should be the path to a _temporary_ kubeconfig file" && exit 1
 
 CONFTEMP="$1"
 
 [ ! -f "$CONFTEMP" ] && echo "Temporary file $CONFTEMP not found. No import performed." && exit 1
 
-[ -z "$KUBECONFIG" ] && echo "This script requires a KUBECONFIG env. Aborting merge." && exit 1
+[ -z "${KUBECONFIG:-}" ] && echo "This script requires a KUBECONFIG env. Aborting merge." && exit 1
 
 if [ -f "$KUBECONFIG" ]; then
   echo "Target kubeconfig $KUBECONFIG already exists. Merging."
+  # note: current-context becomes whatever CONFTEMP set, because CONFTEMP is listed
+  # first in KUBECONFIG and --flatten preserves the merged current-context.
   KUBECONFIG="$CONFTEMP:$KUBECONFIG" kubectl config view --flatten > "$CONFTEMP-merged"
   mv "$CONFTEMP-merged" "$CONFTEMP"
 else