fix(mqtt): rebuild topics in runOnce when the root changes

Replaces the per-call-site reinitTopics() calls. Also keep the device state and node database segments when the EU clamp swaps the region.

src/graphics/draw/MenuHandler.cpp

@@ -28,9 +28,6 @@
 #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/GeofenceModule.h"
 #include "modules/KeyVerificationModule.h"
@@ -295,10 +292,6 @@ static void applyLoraRegion(meshtastic_Config_LoRaConfig_RegionCode region, bool
     if (strncmp(moduleConfig.mqtt.root, default_mqtt_root, strlen(default_mqtt_root)) == 0) {
         snprintf(moduleConfig.mqtt.root, sizeof(moduleConfig.mqtt.root), "%s/%s", default_mqtt_root, myRegion->name);
         changes |= SEGMENT_MODULECONFIG;
-#if !MESHTASTIC_EXCLUDE_MQTT
-        if (mqtt)
-            mqtt->reinitTopics();
-#endif
     }
 #if !MESHTASTIC_EXCLUDE_GPS
     // Enable gps if it was previously disabled due to region not being set

src/modules/AdminModule.cpp

@@ -1071,10 +1071,6 @@ 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
                     snprintf(moduleConfig.mqtt.root, sizeof(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 {
@@ -1115,12 +1111,8 @@ 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
                     snprintf(moduleConfig.mqtt.root, sizeof(moduleConfig.mqtt.root), "%s/%s", default_mqtt_root, myRegion->name);
-#if !MESHTASTIC_EXCLUDE_MQTT
-                    if (mqtt)
-                        mqtt->reinitTopics();
-#endif
                 }
-                changes = SEGMENT_CONFIG | SEGMENT_MODULECONFIG;
+                changes |= SEGMENT_CONFIG | SEGMENT_MODULECONFIG;
             }
             //  use_preset and bandwidth are coerced into valid values by the check.
         }

src/mqtt/MQTT.cpp

@@ -376,6 +376,7 @@ void mqttInit()
 
 void MQTT::reinitTopics()
 {
+    topicRoot = moduleConfig.mqtt.root;
     const std::string root = *moduleConfig.mqtt.root ? moduleConfig.mqtt.root : default_mqtt_root;
     cryptTopic = root + "/2/e/";
     mapTopic = root + "/2/map/";
@@ -580,6 +581,9 @@ int32_t MQTT::runOnce()
 {
     if (!moduleConfig.mqtt.enabled || !(moduleConfig.mqtt.map_reporting_enabled || channels.anyMqttEnabled()))
         return disable();
+    // A region change rewrites the root at runtime, from several call sites
+    if (topicRoot != moduleConfig.mqtt.root)
+        reinitTopics();
     bool wantConnection = wantsLink();
 
     perhapsReportToMap();

src/mqtt/MQTT.h

@@ -58,9 +58,6 @@ class MQTT : private concurrency::OSThread
     bool isUsingDefaultServer() { return isConfiguredForDefaultServer; }
     bool isUsingDefaultRootTopic() { return isConfiguredForDefaultRootTopic; }
 
-    /// Rebuild topics from moduleConfig.mqtt.root and force a resubscribe.
-    void reinitTopics();
-
     /// Validate the meshtastic_ModuleConfig_MQTTConfig.
     static bool isValidConfig(const meshtastic_ModuleConfig_MQTTConfig &config) { return isValidConfig(config, nullptr); }
 
@@ -101,6 +98,7 @@ class MQTT : private concurrency::OSThread
     explicit MQTT(std::unique_ptr<MQTTClient> mqttClient);
 #endif
 
+    std::string topicRoot;            // moduleConfig.mqtt.root the topics below were built from
     std::string cryptTopic = "/2/e/"; // msh/2/e/CHANNELID/NODEID
     std::string mapTopic = "/2/map/"; // For protobuf-encoded MapReport messages
 
@@ -114,6 +112,9 @@ class MQTT : private concurrency::OSThread
      */
     void reconnect();
 
+    /// Rebuild topics from moduleConfig.mqtt.root and force a resubscribe.
+    void reinitTopics();
+
     /** Tell the server what subscriptions we want (based on channels.downlink_enabled)
      */
     void sendSubscriptions();

test/test_mqtt/MQTT.cpp

@@ -1360,8 +1360,9 @@ 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.
+// A LoRa region change rewrites moduleConfig.mqtt.root without telling MQTT (AdminModule, MenuHandler,
+// InkHUD). runOnce() must pick it up, rebuild the topics and resubscribe; otherwise the node keeps
+// publishing and subscribing under the old region's root until reboot.
 void test_reinitTopicsUpdatesOnRegionChange(void)
 {
     // Start MQTT with a US region root.
@@ -1371,11 +1372,10 @@ void test_reinitTopicsUpdatesOnRegionChange(void)
     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().
+    // Simulate region change: only the root changes, nobody notifies MQTT.
     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([] {