fix: production hardening — safety fixes, prediction accuracy, test coverage

Safety:
- Async input handler: await all handleInput() calls, prevents unhandled rejections
- Fix emergencyStop case mismatch: "emergencyStop" → "emergencystop" matching config
- Implement showCoG() method (was routing to undefined)
- Null guards on 6 methods for missing curve data
- Editor menu polling timeout (5s max)
- Listener cleanup on node close (child measurements + state emitter)
- Tick loop race condition: track startup timeout, clear on close

Prediction accuracy:
- Remove efficiency rounding that destroyed signal in canonical units
- Fix calcEfficiency variant: hydraulic power reads from correct variant
- Guard efficiency calculations against negative/zero values
- Division-by-zero protection in calcRelativeDistanceFromPeak
- Curve data anomaly detection (cross-pressure median-y ratio check)
- calcEfficiencyCurve O(n²) → O(n) with running min
- updateCurve bootstraps predictors when they were null

Tests: 43 new tests (76 total) covering emergency stop, shutdown/maintenance
sequences, efficiency/CoG, movement lifecycle, output format, null guards,
and listener cleanup.

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

test/integration/shutdown-sequence.integration.test.js

@@ -0,0 +1,72 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const Machine = require('../../src/specificClass');
+const { makeMachineConfig, makeStateConfig } = require('../helpers/factories');
+
+test('shutdown sequence from operational reaches idle', async () => {
+  const machine = new Machine(makeMachineConfig(), makeStateConfig());
+
+  await machine.handleInput('parent', 'execSequence', 'startup');
+  assert.equal(machine.state.getCurrentState(), 'operational');
+
+  await machine.handleInput('parent', 'execSequence', 'shutdown');
+  assert.equal(machine.state.getCurrentState(), 'idle');
+});
+
+test('shutdown from operational ramps down position before stopping', async () => {
+  const machine = new Machine(makeMachineConfig(), makeStateConfig());
+
+  await machine.handleInput('parent', 'execSequence', 'startup');
+  await machine.handleInput('parent', 'execMovement', 50);
+
+  const posBefore = machine.state.getCurrentPosition();
+  assert.ok(posBefore > 0, 'Machine should be at non-zero position');
+
+  await machine.handleInput('parent', 'execSequence', 'shutdown');
+
+  const posAfter = machine.state.getCurrentPosition();
+  assert.ok(posAfter <= posBefore, 'Position should have decreased after shutdown');
+  assert.equal(machine.state.getCurrentState(), 'idle');
+});
+
+test('shutdown clears predicted flow and power', async () => {
+  const machine = new Machine(makeMachineConfig(), makeStateConfig());
+
+  await machine.handleInput('parent', 'execSequence', 'startup');
+  machine.updateMeasuredPressure(1000, 'downstream', { timestamp: Date.now(), unit: 'mbar', childName: 'pt' });
+  await machine.handleInput('parent', 'execMovement', 50);
+
+  await machine.handleInput('parent', 'execSequence', 'shutdown');
+
+  const flow = machine.measurements.type('flow').variant('predicted').position('downstream').getCurrentValue();
+  const power = machine.measurements.type('power').variant('predicted').position('atEquipment').getCurrentValue();
+  assert.equal(flow, 0, 'Flow should be zero after shutdown');
+  assert.equal(power, 0, 'Power should be zero after shutdown');
+});
+
+test('entermaintenance sequence from operational reaches maintenance state', async () => {
+  const machine = new Machine(makeMachineConfig(), makeStateConfig());
+
+  await machine.handleInput('parent', 'execSequence', 'startup');
+  assert.equal(machine.state.getCurrentState(), 'operational');
+
+  await machine.handleInput('parent', 'enterMaintenance', 'entermaintenance');
+  assert.equal(machine.state.getCurrentState(), 'maintenance');
+});
+
+test('exitmaintenance requires mode with exitmaintenance action allowed', async () => {
+  const machine = new Machine(makeMachineConfig(), makeStateConfig());
+
+  // Use auto mode (has execsequence + entermaintenance) to reach maintenance
+  await machine.handleInput('parent', 'execSequence', 'startup');
+  assert.equal(machine.state.getCurrentState(), 'operational');
+
+  await machine.handleInput('parent', 'enterMaintenance', 'entermaintenance');
+  assert.equal(machine.state.getCurrentState(), 'maintenance');
+
+  // Switch to fysicalControl which allows exitmaintenance
+  machine.setMode('fysicalControl');
+  await machine.handleInput('fysical', 'exitMaintenance', 'exitmaintenance');
+  assert.equal(machine.state.getCurrentState(), 'idle');
+});