ralph-wiggum: bash 3.2 runtime error in setup-ralph-loop.sh (empty array + set -u)

Bug

plugins/ralph-wiggum/scripts/setup-ralph-loop.sh line 113 crashes on macOS (bash 3.2.57) when PROMPT_PARTS is an empty array and set -u is active:

PROMPT="${PROMPT_PARTS[*]}"  # unbound variable error under bash 3.2 + set -u

Environment

• macOS (Darwin 25.3.0, arm64)
• /bin/bash = GNU bash 3.2.57 (Apple ships this due to GPLv3)
• Claude Code 2.1.x

Fix

The official ralph-loop plugin (in claude-plugins-official) already has the fix at the same line:

PROMPT="${PROMPT_PARTS[*]:-}"  # bash 3.2 compatible

The :- default parameter expansion prevents the unbound variable error when the array is empty.

Additional context

The ralph-loop plugin also added session isolation (session_id tracking) which ralph-wiggum lacks. These may be worth porting as well.