feat(mqtt): adopt mqttastic-client-kmp 0.2.0 — disconnect reasons + Test Connection (#5181)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

core/model/src/commonMain/kotlin/org/meshtastic/core/model/MqttConnectionState.kt

@@ -16,20 +16,41 @@
  */
 package org.meshtastic.core.model
 
-/** App-level MQTT proxy connection state, decoupled from the MQTT library's internal type. */
-enum class MqttConnectionState {
+/**
+ * App-level MQTT proxy connection state, decoupled from the MQTT library's internal type.
+ *
+ * Modeled as a sealed class so disconnect / reconnect events can carry diagnostic context — the user-facing reason for
+ * an unexpected disconnect, or the most recent reconnect attempt failure — without requiring downstream consumers to
+ * depend on the MQTT library's exception types.
+ */
+sealed class MqttConnectionState {
     /** The MQTT proxy has not been started (disabled or not yet initialized). */
-    INACTIVE,
-
-    /** The MQTT client is not connected to the broker. */
-    DISCONNECTED,
+    data object Inactive : MqttConnectionState()
 
     /** The MQTT client is actively connecting to the broker. */
-    CONNECTING,
+    data object Connecting : MqttConnectionState()
 
     /** The MQTT client is connected and subscribed to topics. */
-    CONNECTED,
+    data object Connected : MqttConnectionState()
 
-    /** The MQTT client lost connection and is attempting to reconnect. */
-    RECONNECTING,
+    /**
+     * The MQTT client lost connection and is attempting to reconnect.
+     *
+     * @property attempt 1-based attempt counter for the current reconnect loop.
+     * @property lastError Localized message from the most recent reconnect failure, if any.
+     */
+    data class Reconnecting(val attempt: Int = 0, val lastError: String? = null) : MqttConnectionState()
+
+    /**
+     * The MQTT client is not connected to the broker.
+     *
+     * @property reason Localized failure message for an unexpected disconnect, or `null` for the idle / initial /
+     *   intentional-close case (use [Idle]).
+     */
+    data class Disconnected(val reason: String? = null) : MqttConnectionState() {
+        companion object {
+            /** Singleton for the idle / no-reason disconnected state. */
+            val Idle: Disconnected = Disconnected(reason = null)
+        }
+    }
 }

core/model/src/commonMain/kotlin/org/meshtastic/core/model/MqttProbeStatus.kt

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.model
+
+/**
+ * UI-friendly outcome of a one-shot MQTT broker reachability probe.
+ *
+ * Mirrors the failure shapes of `org.meshtastic.mqtt.ProbeResult` but stays in the model module so feature/UI code can
+ * consume the result without depending on the MQTT library.
+ */
+sealed class MqttProbeStatus {
+    /** Probe is currently in flight. */
+    data object Probing : MqttProbeStatus()
+
+    /**
+     * Broker accepted the connection. [serverInfo] is a short human-readable summary of any CONNACK properties that are
+     * useful to surface to the user.
+     */
+    data class Success(val serverInfo: String?) : MqttProbeStatus()
+
+    /** Broker rejected the connection (CONNACK with non-zero reason code). */
+    data class Rejected(val reasonCode: Int, val reason: String?, val serverReference: String?) : MqttProbeStatus()
+
+    /** DNS lookup failed. */
+    data class DnsFailure(val message: String?) : MqttProbeStatus()
+
+    /** TCP socket could not be opened. */
+    data class TcpFailure(val message: String?) : MqttProbeStatus()
+
+    /** TLS handshake failed. */
+    data class TlsFailure(val message: String?) : MqttProbeStatus()
+
+    /** Probe exceeded its timeout. */
+    data class Timeout(val timeoutMs: Long) : MqttProbeStatus()
+
+    /** Any other / unclassified failure. */
+    data class Other(val message: String?) : MqttProbeStatus()
+}