feat(mgc-config + state): planner.useRendezvous schema + remaining-transition reads

Three coherent additions that the MGC rendezvous planner depends on:

- machineGroupControl.json: new `planner.useRendezvous` boolean (default
  true). Used by both `_optimalControl` and `equalFlowControl` (via the
  shared `_dispatchFlowDistribution` helper) to gate same-time-landing.

- state.js: external aborts (returnToOperational=false) bump a monotonic
  `sequenceAbortToken`. executeSequence captures it at entry and bails
  out of its for-loop if it advances mid-sequence, so a shutdown that's
  past its ramp-down step doesn't barge through stopping → coolingdown
  when a fresher demand re-engages the pump.

- stateManager.js: new `getRemainingTransitionS()` returns the seconds
  remaining in a timed state by reading the wall-clock entry timestamp.
  buildProfile() reads it so the planner can compute exact eta for a
  child that's currently mid-ladder (warmingup / starting / cooling).

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

src/state/stateManager.js

@@ -39,6 +39,11 @@
 class stateManager {
   constructor(config, logger) {
     this.currentState = config.state.current;
+    // Wall-clock entry timestamp into currentState. Used by
+    // getRemainingTransitionS() so callers (e.g. MGC movement planner)
+    // can compute exact remaining time for timed states without
+    // approximating from the full configured duration.
+    this.stateEnteredAt = Date.now();
     this.availableStates = config.state.available;
     this.descriptions = config.state.descriptions;
     this.logger = logger;
@@ -63,7 +68,18 @@ class stateManager {
   getCurrentState() {
     return this.currentState;
   }
-  
+
+  // Seconds remaining in the current timed state (warmingup, coolingdown,
+  // starting, stopping, …). Returns 0 for untimed states or once the
+  // configured duration has elapsed. The MGC movement planner uses this to
+  // compute exact rendezvous time for protected (non-interruptible) states.
+  getRemainingTransitionS() {
+    const d = this.transitionTimes?.[this.currentState] || 0;
+    if (d <= 0) return 0;
+    const elapsed = (Date.now() - this.stateEnteredAt) / 1000;
+    return Math.max(0, d - elapsed);
+  }
+
   transitionTo(newState,signal) {
     return new Promise((resolve, reject) => {
       if (signal && signal.aborted) {
@@ -89,6 +105,7 @@ class stateManager {
       if (transitionDuration > 0) {
         const timeoutId = setTimeout(() => {
           this.currentState = newState;
+          this.stateEnteredAt = Date.now();
           resolve(`Transition from ${this.currentState} to ${newState} completed in ${transitionDuration}s.`);
         }, transitionDuration * 1000);
         if (signal) {
@@ -99,6 +116,7 @@ class stateManager {
         }
       } else {
         this.currentState = newState;
+        this.stateEnteredAt = Date.now();
         resolve(`Immediate transition to ${this.currentState} completed.`);
       }
     });