fix(issue-50): the loop path waits by the registry on its pending record (review F1-F3)

F1: from phase two on, the loop's `_registry_wait` ran before the record was
reset to pending, so the waiter held a terminal record: the engine refused its
dispatch_wait_at merge and other waiters never saw it in the FIFO. The wait
(and the idle wait after it) now follows the `--status pending` update; s1
pins the order and u3c shows why a terminal self record cannot signal.
F2: the real-herdr box teardown survives a hung stop/delete, kills a server
bootstrapped by a late client call, and asserts the server and HOME are gone.
F3: the delegate-job SKILL.md exit 5 row names the registry wait.
Also drops the dead loop in s1.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

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

@@ -104,7 +104,7 @@ Under fail-closed operation (`MAM_DELEGATE_FAIL_CLOSED=1`, default), the CLI ret
 | `2` | Timeout | `error` (`deadline_timeout`) | Subscriber idle timeout (K x N without an event; the total budget is the wall-clock row below). **R1 liveness grace (Issue #18)**: after the subscriber idles out the wrapper keeps re-observing the disk while the job's events.log shows an event at most K x N (`--idle-timeout`) old - the automatic heartbeat counts - up to the wall-clock `--timeout`. herdr status and the pane are logged as a diagnostic only. |
 | `2` | Wall clock | `error` (`wall_clock_timeout`) | The budget (`--timeout`) ran out, events or not (Issue #33; was `deadline_timeout` before v4.8.0). |
 | `3` | Broker Error | `error` (`wall_clock_timeout` once the budget is spent, else `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). |
+| `5` | Session Busy | `cancelled` (`session_busy`) | Precondition failed / `session_busy`: Preflight check (`preflight_agent`) or TUI idle handshake wait failed, or the session's open jobs in the registry did not end within `MAM_DISPATCH_WAIT_S` (Issue #50) (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.