fix(issue-6): fail-closed registry timeout and TUI turn handshake

- Introduce finalize_unfinished in multi-agent-mux-delegate-job for fail-closed atomic transitions
- Enforce CAS dispatch_token and attempt_id pinning across engine, CLI, and lifecycle scripts
- Integrate Herdr wait_for_agent_idle turn handshake to prevent prompt loss and race conditions
- Resolve bash 3.2 set -u empty array expansion compatibility in lib.sh
- Preserve Issue #5 R2 contract in CAS transition engine (engine.py, publish_event.py, service.py)
- Add comprehensive regression suites (test_issue6_fail_closed.py, test_issue6_turn_handshake.py)
- Bump lockstep framework and skills to v4.4.1 across lib.sh, eager.py, VERSIONS.md, 8 SKILL.md
- Synchronize documentation (IMPROVEMENTS.md, MESSAGING.md, state-transitions.md, task.md, phase5-e2e.md)
- Unanimous PASS achieved across 4 reviewer team leaders (Claude, Codex, OpenCode, Grok)

Closes #6

tests/test_b19_headless_reconcile_fixes.py

@@ -207,7 +207,7 @@ LOG=/tmp/mam-d5-sks.$$
 : > "$LOG"
 _sks_herdr() {
   echo "$*" >> "$LOG"
-  if [ "${1:-}" = "agent" ] && [ "${2:-}" = "prompt" ]; then return 1; fi
+  if [ "${1:-}" = "agent" ] && [ "${2:-}" = "prompt" ]; then echo "unknown command: agent prompt" >&2; return 1; fi
   if [ "${1:-}" = "paste-buffer" ]; then return 1; fi
   return 0
 }