fix(mqtt): log throwable-less client errors at warn (#6493)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

core/network/src/commonMain/kotlin/org/meshtastic/core/network/repository/KermitMqttLogger.kt

@@ -49,12 +49,11 @@ class KermitMqttLogger(
 
             MqttLogLevel.WARN -> logger.w(throwable) { message }
 
-            // The library reports a broker that closed the socket, an unreachable host, or Wi-Fi dropping mid-read at
-            // ERROR ("Read loop error: Not enough data available"), and the client then reconnects on its own. Those
-            // are expected for a mobile client and dominated our error tracking, so log them at WARN — diagnosable in
-            // a support session, but not counted as application errors.
+            // The library logs its connection lifecycle at ERROR — broker socket close, unreachable host, Wi-Fi drop —
+            // and reconnects itself; broker rejections arrive without a throwable and are user config, surfaced via
+            // MqttProbeStatus. Neither is an app defect, so both log at WARN. Real faults carry a throwable.
             MqttLogLevel.ERROR ->
-                if (throwable?.isExpectedConnectionFailure() == true) {
+                if (throwable == null || throwable.isExpectedConnectionFailure()) {
                     logger.w(throwable) { message }
                 } else {
                     logger.e(throwable) { message }

core/network/src/commonTest/kotlin/org/meshtastic/core/network/repository/KermitMqttLoggerTest.kt

@@ -67,10 +67,36 @@ class KermitMqttLoggerTest {
     }
 
     @Test
-    fun `an error with no throwable stays an error`() {
+    fun `an error with no throwable is downgraded to WARN`() {
+        // A bare message carries no stack or type to triage, so it must not count as an application error.
         mqttLogger.log(level = MqttLogLevel.ERROR, tag = "MqttClient", message = "boom", throwable = null)
 
-        assertEquals(Severity.Error, writer.entries.single().first)
+        assertEquals(Severity.Warn, writer.entries.single().first)
+    }
+
+    @Test
+    fun `a connection teardown log is not reported as an application error`() {
+        mqttLogger.log(
+            level = MqttLogLevel.ERROR,
+            tag = "MqttConnection",
+            message = "Fatal error — tearing down connection",
+            throwable = null,
+        )
+
+        assertEquals(Severity.Warn, writer.entries.single().first)
+    }
+
+    @Test
+    fun `a broker rejection is a user configuration problem rather than an application error`() {
+        // Surfaced to the user through MqttProbeStatus, so it is not an app defect.
+        mqttLogger.log(
+            level = MqttLogLevel.ERROR,
+            tag = "MqttConnection",
+            message = "Connection refused: BAD_USER_NAME_OR_PASSWORD",
+            throwable = null,
+        )
+
+        assertEquals(Severity.Warn, writer.entries.single().first)
     }
 
     @Test