fix(level): pass timestamp on level samples for level-rate fallback

MeasurementRouter.onLevelMeasurement was writing level samples via
.value(value).unit(context.unit), which dropped the timestamp. The
level-rate fallback in FlowAggregator derives netFlow from dlevel/dt,
so without a timestamp on each sample it had nothing to differentiate.

Switch to the positional .value(value, timestamp, unit) form so the
fallback works. Add a basic test that drives two level samples 2 s
apart and asserts the aggregator produces direction=filling with a
finite dlevel/dt-derived netFlow.

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

src/measurement/measurementRouter.js

@@ -34,7 +34,7 @@ class MeasurementRouter {
 
   onLevelMeasurement(position, value, context = {}) {
     this.measurements.type('level').variant('measured').position(position)
-      .value(value).unit(context.unit);
+      .value(value, context.timestamp, context.unit);
 
     const series = this.measurements.type('level').variant('measured').position(position);
     const levelMeters = series.getCurrentValue('m');

test/basic/specificClass.test.js

@@ -4,6 +4,7 @@
 const test = require('node:test');
 const assert = require('node:assert/strict');
 
+const { MeasurementContainer } = require('generalFunctions');
 const PumpingStation = require('../../src/specificClass');
 
 // machineGroups is a registry-backed getter (declareChildGetter) — direct
@@ -84,6 +85,39 @@ function makeConfig(overrides = {}) {
   return base;
 }
 
+function makeMeasurementChild({ type = 'level', position = 'atequipment', name = 'child-level' } = {}) {
+  return {
+    config: {
+      general: { id: name, name },
+      functionality: { positionVsParent: position },
+      asset: { type },
+    },
+    measurements: new MeasurementContainer({
+      autoConvert: true,
+      preferredUnits: { level: 'm', flow: 'm3/s', pressure: 'Pa' },
+    }),
+  };
+}
+
+test('level child subscription records one sample per event for level-rate fallback', async () => {
+  const ps = new PumpingStation(makeConfig());
+  const child = makeMeasurementChild();
+
+  ps._subscribeMeasurement(child);
+  child.measurements.type('level').variant('measured').position('atequipment')
+    .value(1.0, 1000, 'm');
+  child.measurements.type('level').variant('measured').position('atequipment')
+    .value(1.1, 3000, 'm');
+
+  const series = ps.measurements.type('level').variant('measured').position('atequipment').get();
+  assert.deepEqual(series.values, [1.0, 1.1]);
+
+  const net = ps.flowAggregator.selectBestNetFlow();
+  assert.equal(net.source, 'level:measured');
+  assert.equal(net.direction, 'filling');
+  assert.ok(Math.abs(net.value - 0.5) < 1e-9, `net flow was ${net.value}`);
+});
+
 test('Basin geometry — derived values', async (t) => {
   const ps = new PumpingStation(makeConfig());