diff --git a/scripts/dev/agent.sh b/scripts/dev/agent.sh
index 823e8e3..ae79daf 100755
--- a/scripts/dev/agent.sh
+++ b/scripts/dev/agent.sh
@@ -3,6 +3,8 @@
 # EXIT: 0 ok, 1 preflight, 2 operation failed.
 set -euo pipefail
 
+trap 'echo "agent.sh: failed at line $LINENO (exit $?)" >&2' ERR
+
 RESERVED_NAMES=(master main HEAD list merge clean new)
 MAX_WORKTREES=4
 
@@ -73,9 +75,13 @@ age_str() {
 
 validate_name() {
   local name="$1"
-  [[ "$name" =~ ^[a-z][a-z0-9-]*$ ]] || prefail "name '$name' must match ^[a-z][a-z0-9-]*$"
+  if ! [[ "$name" =~ ^[a-z][a-z0-9-]*$ ]]; then
+    prefail "name '$name' must match ^[a-z][a-z0-9-]*$"
+  fi
   for r in "${RESERVED_NAMES[@]}"; do
-    [ "$name" = "$r" ] && prefail "'$name' is a reserved word"
+    if [ "$name" = "$r" ]; then
+      prefail "'$name' is a reserved word"
+    fi
   done
 }