Minimal repro: GLOBAL defer queue (dzn) vs per-component LOCAL defer queues (ours).

Main.start() calls a.go() then b.go() in one RTC, so the two Worker subcomponents'
deferred `done` notifications are ENQUEUED in the fixed order [a, b].

dzn (System_golden.aut, `dzn graph -b lts -f aut -m System`): discharge order is
STRICTLY m.aDone then m.bDone — one global FIFO, head-of-queue discharges first.

ours (`nucleos lts -m System`): BOTH m.aDone-then-m.bDone AND m.bDone-then-m.aDone
are reachable — the composition interleaves each leaf's defer discharge independently.

ltscompare (-eweak-trace, dzn m.inevitable->tau):
  not equal;  dzn ⊑ ours (true);  ours ⊑ dzn (FALSE).
So our system-LTS is a strict trace SUPERSET of dzn's: we admit the local-queue
interleaving (b before a) that the global FIFO forbids. The composition lacks the
global defer-queue synchronization.

DESIGN — global defer-queue synchronization (fix plan):
Add explicit sync labels <defer-qin> (enqueue) and <defer-cancel>(n) (cancel) to
the leaf LTS alongside the existing <defer> (discharge). A FIFO monitor process,
synchronized into the layered binary product, tracks the global queue and gates
<defer>: only the head leaf's <defer> is enabled.
  - INTERMEDIATE LTSs keep all three labels (the nested repro proves <defer-qin>
    must propagate up so an outer monitor can gate on enqueues deep inside a Sub).
  - FINAL top-level LTS HIDES <defer-qin> and <defer-cancel> (-> tau, then reduce);
    <defer> stays visible (dzn keeps it). <defer-cancel> indices are recomputed as
    the global queue grows across layers.
ACCEPTANCE: ours-with-monitor, hide(<defer-qin>,<defer-cancel>), bisim-reduce,
must equal the golden (dzn alphabet: <defer> <illegal> m.* tau — no qin/cancel).

GOLDEN NOTE: *_golden.aut is generated via scripts/lbs-system-golden.sh (inspect-ports + dzn graph + lbs_system_transform.py), which strips dzn's known provides-port .inevitable BUG (+ tau self-loops, fork-at-reply). Validate with: NUC_DEFER_SYNC=1 NUC_RTCPROD=1 nucleos lts -m <C> | wf-check.py aut - <golden> --system.
