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_issue5_phase1_delegation.py

@@ -327,7 +327,7 @@ def test_registry_cli_contract_snapshot(mam_sandbox):
     assert subparsers, "registry must expose subcommands"
     commands = set(subparsers[0].choices)
     assert commands == {
-        "register", "list", "get", "status", "update", "get-feedback", "pick", "logs",
+        "register", "list", "get", "status", "update", "close", "get-feedback", "pick", "logs",
     }, commands
     reg = _parser_snapshot(subparsers[0].choices["register"])
     assert reg["--prompt"][2] is None