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

.agents/skills/multi-agent-mux-delegate-job/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: multi-agent-mux-delegate-job
 description: "Delegate a unit of work to any autonomous agent (claude-code, hermes, agy, grok-build, codex, or a human) and observe it asynchronously over an MQTT event channel. Supported roles include orchestrator, worker, and reviewer."
-version: 4.4.0
+version: 4.4.1
 author: godopu
 license: MIT
 platforms: [linux, macos, windows]
@@ -70,6 +70,22 @@ For detailed state machine diagrams and configurations, see [DELEGATION_TYPES.md
 
 ---
 
+## Exit Codes & Failure Handling
+
+Under fail-closed operation (`MAM_DELEGATE_FAIL_CLOSED=1`, default), the CLI returns deterministic exit codes:
+
+| Exit Code | Meaning | Final Registry Status | Failure Behavior & Resilience |
+|:---:|:---:|:---:|---|
+| `0` | Success | `completed` | Job succeeded and completed event received or verified on disk with approval (`PASS`/`AGREE`). |
+| `1` | Failure | `error` | Execution failure / Agent injection error (`inject_agent`). |
+| `2` | Timeout | `error` (`deadline_timeout`) | Subscriber timeout (total budget or idle timeout reached without terminal event). **R1 Working-Agent Resilience**: If the agent in Herdr is still actively `working`, the wrapper does not immediately fail-close; it re-observes disk status at intervals up to the wall-clock `--timeout` deadline before fail-closing. |
+| `3` | Broker Error | `error` (`deadline_timeout`) | Broker unavailable (`MQTT_BROKER_UNAVAILABLE`) and terminal status not found on disk during deadline. |
+| `5` | Session Busy | `cancelled` (`session_busy`) | Precondition failed / `session_busy`: Preflight check (`preflight_agent`) or TUI idle handshake wait failed (prompt never delivered, retryable). |
+
+In all execution paths, the final line of standard output prints the persistent audit log directory path (`<logs_root>/<job_id>`), fulfilling the parsing contract for orchestrator runners.
+
+---
+
 ## Where the Implementation Lives (v4.3.0)
 
 The implementation moved to the `lib_py.delegation` package in issue #5 phase 1.