B2.3: migrate MGC to LatestWinsGate.fireAndWait

specificClass.js 319 → 311 lines. Removed inline _dispatchInFlight +
_delayedCall + finally block. handleInput is now a 1-line delegate
to DemandDispatcher.fireAndWait({source, demand, ...}).
turnOffAllMachines calls _demandDispatcher.cancelPending().
DemandDispatcher 39 → 53 lines. One integration test rewritten to
use the new sentinel-resolution semantics. 77/77 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/integration/turnoff-deadlock.integration.test.js

@@ -116,16 +116,27 @@ test('repeated turnOffAllMachines reaches idle (serializes concurrent shutdowns)
     'delayedMove must be cleared after shutdown');
 });
 
-test('turnOffAllMachines clears MGC._delayedCall to cancel any deferred dispatch', async () => {
+test('turnOffAllMachines cancels any parked demand so it cannot re-engage pumps', async () => {
   // PS sends a 1% keep-alive while MGC is mid-dispatch. MGC parks it in
-  // _delayedCall. PS then crosses stopLevel and calls turnOffAllMachines.
-  // Without clearing _delayedCall, MGC's finally block fires the parked
-  // 1% call AFTER the shutdown — re-engaging the pump.
+  // its demand dispatcher's latest-wins slot. PS then crosses stopLevel
+  // and calls turnOffAllMachines. Without cancelPending(), the parked
+  // 1% call would fire AFTER the shutdown — re-engaging the pump.
   const { mgc } = buildGroup();
-  mgc._delayedCall = { source: 'parent', demand: 1, powerCap: Infinity, priorityList: null };
+  const gate = mgc._demandDispatcher._gate;
+  // Pin a fake in-flight dispatch then park a pending call behind it.
+  gate._inFlight = true;
+  const parked = mgc.handleInput('parent', 1, Infinity, null);
 
   await mgc.turnOffAllMachines();
 
-  assert.equal(mgc._delayedCall, null,
-    'turnOff must cancel any deferred dispatch so it cannot re-engage pumps post-shutdown');
+  // Re-open the gate: the in-flight pin is artificial. Awaiting the
+  // parked promise must yield the SUPERSEDED sentinel (i.e. it was
+  // cancelled, not run).
+  const res = await parked;
+  assert.ok(res && res.superseded === true,
+    'parked demand must resolve as superseded after turnOffAllMachines cancels it');
+  // Idle now — pending slot must be clear.
+  assert.equal(gate._pending, null,
+    'turnOff must cancel any parked demand so it cannot re-engage pumps post-shutdown');
+  gate._inFlight = false;
 });