fix(hooks): replace heredoc with printf to fix bash 5.3+ hang

Bash 5.3 has a regression where heredoc variable expansion blocks when
content exceeds ~512 bytes. The session_context variable is ~4,500 bytes,
causing the SessionStart hook to hang indefinitely on macOS with Homebrew
bash 5.3+. Replace cat <<EOF with printf.

Tested on Linux (bash 5.2) and Windows (Git Bash 5.2). The hang only
affects 5.3+ but printf works correctly on all versions.

Based on #572, closes #572. Fixes #571.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hooks/session-start

@@ -39,23 +39,16 @@ session_context="<EXTREMELY_IMPORTANT>\nYou have superpowers.\n\n**Below is the
 # Claude Code hooks expect hookSpecificOutput.additionalContext.
 # Claude Code reads BOTH fields without deduplication, so we must only
 # emit the field consumed by the current platform to avoid double injection.
+#
+# Uses printf instead of heredoc (cat <<EOF) to work around a bash 5.3+
+# bug where heredoc variable expansion hangs when content exceeds ~512 bytes.
+# See: https://github.com/obra/superpowers/issues/571
 if [ -n "${CLAUDE_PLUGIN_ROOT:-}" ]; then
   # Claude Code sets CLAUDE_PLUGIN_ROOT — emit only hookSpecificOutput
-  cat <<EOF
-{
-  "hookSpecificOutput": {
-    "hookEventName": "SessionStart",
-    "additionalContext": "${session_context}"
-  }
-}
-EOF
+  printf '{\n  "hookSpecificOutput": {\n    "hookEventName": "SessionStart",\n    "additionalContext": "%s"\n  }\n}\n' "$session_context"
 else
   # Other platforms (Cursor, etc.) — emit only additional_context
-  cat <<EOF
-{
-  "additional_context": "${session_context}"
-}
-EOF
+  printf '{\n  "additional_context": "%s"\n}\n' "$session_context"
 fi
 
 exit 0