fix(mqtt): drop undeclared jsonTopic refs in reinitTopics()

reinitTopics() assigned to a jsonTopic member that does not exist on this
branch (the MQTT class only has cryptTopic and mapTopic), so MQTT.cpp failed
to compile ("'jsonTopic' was not declared in this scope") and broke every
build that compiles it. Remove the jsonTopic lines so reinitTopics() rebuilds
exactly the topics the original constructor did.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/graphics/draw/MenuHandler.cpp

@@ -23,6 +23,9 @@
 #include "mesh/RadioLibInterface.h"
 #include "modules/AdminModule.h"
 #include "modules/CannedMessageModule.h"
+#if !MESHTASTIC_EXCLUDE_MQTT
+#include "mqtt/MQTT.h"
+#endif
 #include "modules/ExternalNotificationModule.h"
 #include "modules/KeyVerificationModule.h"
 #include "modules/TraceRouteModule.h"
@@ -259,6 +262,11 @@ void menuHandler::LoraRegionPicker(uint32_t duration)
                 //  Default broker is in use, so subscribe to the appropriate MQTT root topic for this region
                 sprintf(moduleConfig.mqtt.root, "%s/%s", default_mqtt_root, myRegion->name);
                 changes |= SEGMENT_MODULECONFIG;
+#if !MESHTASTIC_EXCLUDE_MQTT
+                if (mqtt) {
+                    mqtt->reinitTopics();
+                }
+#endif
             }
 
             service->reloadConfig(changes);

src/modules/AdminModule.cpp

@@ -830,6 +830,11 @@ void AdminModule::handleSetConfig(const meshtastic_Config &c, bool fromOthers)
                 if (strncmp(moduleConfig.mqtt.root, default_mqtt_root, strlen(default_mqtt_root)) == 0) {
                     //  Default root is in use, so subscribe to the appropriate MQTT topic for this region
                     sprintf(moduleConfig.mqtt.root, "%s/%s", default_mqtt_root, myRegion->name);
+#if !MESHTASTIC_EXCLUDE_MQTT
+                    if (mqtt) {
+                        mqtt->reinitTopics();
+                    }
+#endif
                 }
                 changes = SEGMENT_CONFIG | SEGMENT_MODULECONFIG;
             } else {

src/mqtt/MQTT.cpp

@@ -303,6 +303,30 @@ void mqttInit()
     new MQTT();
 }
 
+void MQTT::reinitTopics()
+{
+    cryptTopic = "/2/e/";
+    mapTopic = "/2/map/";
+
+    if (*moduleConfig.mqtt.root) {
+        cryptTopic = moduleConfig.mqtt.root + cryptTopic;
+        mapTopic = moduleConfig.mqtt.root + mapTopic;
+        isConfiguredForDefaultRootTopic = isDefaultRootTopic(moduleConfig.mqtt.root);
+    } else {
+        cryptTopic = "msh" + cryptTopic;
+        mapTopic = "msh" + mapTopic;
+        isConfiguredForDefaultRootTopic = true;
+    }
+
+#if HAS_NETWORKING
+    // Force a broker reconnect so subscriptions are refreshed with the new topic prefix
+    if (pubSub.connected()) {
+        pubSub.disconnect();
+    }
+    isConnected = false;
+#endif
+}
+
 #if HAS_NETWORKING
 MQTT::MQTT() : MQTT(std::unique_ptr<MQTTClient>(new MQTTClient())) {}
 MQTT::MQTT(std::unique_ptr<MQTTClient> _mqttClient)
@@ -317,15 +341,7 @@ MQTT::MQTT() : concurrency::OSThread("mqtt"), mqttQueue(MAX_MQTT_QUEUE)
         assert(!mqtt);
         mqtt = this;
 
-        if (*moduleConfig.mqtt.root) {
-            cryptTopic = moduleConfig.mqtt.root + cryptTopic;
-            mapTopic = moduleConfig.mqtt.root + mapTopic;
-            isConfiguredForDefaultRootTopic = isDefaultRootTopic(moduleConfig.mqtt.root);
-        } else {
-            cryptTopic = "msh" + cryptTopic;
-            mapTopic = "msh" + mapTopic;
-            isConfiguredForDefaultRootTopic = true;
-        }
+        reinitTopics();
 
         if (moduleConfig.mqtt.map_reporting_enabled && moduleConfig.mqtt.has_map_report_settings) {
             map_position_precision = Default::getConfiguredOrDefault(moduleConfig.mqtt.map_report_settings.position_precision,

src/mqtt/MQTT.h

@@ -58,6 +58,12 @@ class MQTT : private concurrency::OSThread
     bool isUsingDefaultServer() { return isConfiguredForDefaultServer; }
     bool isUsingDefaultRootTopic() { return isConfiguredForDefaultRootTopic; }
 
+    /** Re-read moduleConfig.mqtt.root and rebuild the topic strings.
+     *  Call this after changing the MQTT root (e.g. on LoRa region change).
+     *  Also forces a broker reconnect so subscriptions are refreshed.
+     */
+    void reinitTopics();
+
     /// Validate the meshtastic_ModuleConfig_MQTTConfig.
     static bool isValidConfig(const meshtastic_ModuleConfig_MQTTConfig &config) { return isValidConfig(config, nullptr); }
 

test/test_mqtt/MQTT.cpp

@@ -815,6 +815,35 @@ void test_customMqttRoot(void)
         [] { return pubsub->subscriptions_.count("custom/2/e/test/+") && pubsub->subscriptions_.count("custom/2/e/PKI/+"); }));
 }
 
+// After a LoRa region change, reinitTopics() updates the publish topic and forces
+// the broker to reconnect with updated subscriptions.
+void test_reinitTopicsUpdatesOnRegionChange(void)
+{
+    // Start MQTT with a US region root.
+    strcpy(moduleConfig.mqtt.root, "msh/US");
+    MQTTUnitTest::restart();
+
+    TEST_ASSERT_TRUE(loopUntil(
+        [] { return pubsub->subscriptions_.count("msh/US/2/e/test/+") && pubsub->subscriptions_.count("msh/US/2/e/PKI/+"); }));
+
+    // Simulate region change: update the root and call reinitTopics().
+    strcpy(moduleConfig.mqtt.root, "msh/EU_868");
+    pubsub->subscriptions_.clear();
+    pubsub->published_.clear();
+    mqtt->reinitTopics();
+
+    // Verify that subscriptions are refreshed with the new region prefix.
+    TEST_ASSERT_TRUE(loopUntil([] {
+        return pubsub->subscriptions_.count("msh/EU_868/2/e/test/+") && pubsub->subscriptions_.count("msh/EU_868/2/e/PKI/+");
+    }));
+
+    // Verify that publish also uses the new topic prefix.
+    mqtt->onSend(encrypted, decoded, 0);
+    TEST_ASSERT_EQUAL(1, pubsub->published_.size());
+    const auto &[topic, payload] = pubsub->published_.front();
+    TEST_ASSERT_EQUAL_STRING("msh/EU_868/2/e/test/!12345678", topic.c_str());
+}
+
 // Empty configuration is valid.
 void test_configEmptyIsValid(void)
 {
@@ -919,6 +948,7 @@ void setup()
     RUN_TEST(test_disabled);
     RUN_TEST(test_mqttInitSkipsAllocationWhenDisabled);
     RUN_TEST(test_customMqttRoot);
+    RUN_TEST(test_reinitTopicsUpdatesOnRegionChange);
     RUN_TEST(test_configEmptyIsValid);
     RUN_TEST(test_configEnabledEmptyIsValid);
     RUN_TEST(test_configWithDefaultServer);