fix: deduplicate predicted-flow child registration + single event subscription

Three bugs in registerChild caused multi-counted outflow in _updatePredictedVolume:

1. machinegroup registered twice (line 66 + line 70 both called
   _registerPredictedFlowChild). Fixed: only register in the
   machinegroup branch.

2. Individual machines registered alongside their machinegroup parent.
   Each pump's predicted flow is already included in MGC's aggregated
   total — subscribing to both triple-counts. Fixed: only register
   individual machines when no machinegroup is present (direct-wired
   pumps without MGC).

3. _registerPredictedFlowChild subscribed to BOTH flow.predicted.downstream
   AND flow.predicted.atequipment events. These carry the same total flow
   on two event names — the handler wrote the value twice per tick.
   Fixed: subscribe to ONE event per child (downstream for outflow,
   upstream for inflow).

These are generalizable patterns:
- When a group aggregator exists, subscribe to IT, not its children.
- One event per measurement type per child — pick the most specific.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/specificClass.js

@@ -63,10 +63,21 @@ class PumpingStation {
       this.stations[child.config.general.id] = child;
     } else if (softwareType === 'machinegroup') {
       this.machineGroups[child.config.general.id] = child;
-      this._registerPredictedFlowChild(child);
     }
 
-    if (softwareType === 'machine' || softwareType === 'pumpingstation' || softwareType === 'machinegroup') {
+    // Register predicted-flow subscription. Only register the HIGHEST-
+    // level aggregator: if a machinegroup is present, subscribe to IT
+    // (its flow.predicted already aggregates all child machines). Do NOT
+    // also subscribe to individual machines — that would double-count
+    // because each pump's flow is included in the group total.
+    //
+    // Individual machines (softwareType='machine') are only subscribed
+    // when there is NO machinegroup parent — i.e., pumps wired directly
+    // to the pumping station without an MGC in between.
+    if (softwareType === 'machinegroup' || softwareType === 'pumpingstation') {
+      this._registerPredictedFlowChild(child);
+    } else if (softwareType === 'machine' && Object.keys(this.machineGroups).length === 0) {
+      // Direct-child machine, no group above it — register its flow.
       this._registerPredictedFlowChild(child);
     }
   }
@@ -97,18 +108,21 @@ class PumpingStation {
     const childId = child.config.general.id ?? childName;
 
     let posKey;
-    let eventNames;
+    let eventName;
     switch (position) {
       case 'downstream':
       case 'out':
       case 'atequipment':
         posKey = 'out';
-        eventNames = ['flow.predicted.downstream', 'flow.predicted.atequipment'];
+        // Subscribe to ONE event only. 'downstream' is the most specific
+        // — avoids double-counting from 'atequipment' which carries the
+        // same total flow on a different event name.
+        eventName = 'flow.predicted.downstream';
         break;
       case 'upstream':
       case 'in':
         posKey = 'in';
-        eventNames = ['flow.predicted.upstream', 'flow.predicted.atequipment'];
+        eventName = 'flow.predicted.upstream';
         break;
       default:
         this.logger.warn(`Unsupported predicted flow position "${position}" from ${childName}`);
@@ -132,7 +146,7 @@ class PumpingStation {
         .value(eventData.value, ts, unit);
     };
 
-    eventNames.forEach((ev) => child.measurements.emitter.on(ev, handler));
+    child.measurements.emitter.on(eventName, handler);
   }
 
   /* --------------------------- Calibration --------------------------- */