Fix UI test timeouts, TypeScript compilation, dependency compatibility, and backend tests with isolated test suite using per-test mocking (#930)

src/spec/mock-mqtt-test.ts

@@ -0,0 +1,40 @@
+import * as mqtt from 'mqtt'
+
+/**
+ * Test-specific MQTT mock (no timers)
+ * 
+ * This mock connects to the broker but doesn't publish any messages automatically.
+ * Each test should publish only the messages it needs via the returned client.
+ * 
+ * This is different from the demo video mock which uses timers.
+ */
+
+let mqttClient: mqtt.MqttClient | null = null
+
+export async function createTestMock(): Promise<mqtt.MqttClient> {
+  if (mqttClient) {
+    return mqttClient
+  }
+
+  return new Promise(resolve => {
+    const client = mqtt.connect('mqtt://127.0.0.1:1883', {
+      username: '',
+      password: '',
+    })
+    client.once('connect', () => {
+      mqttClient = client
+      resolve(client)
+    })
+  })
+}
+
+export function stopTestMock() {
+  if (mqttClient) {
+    try {
+      mqttClient.end()
+      mqttClient = null
+    } catch {
+      // ignore
+    }
+  }
+}