fix: handle GPN Fault in DiscoveringParametersState

When the CPE responds with a CWMP Fault to GetParameterNames,
mark gpnStatus as 'unsupported' and continue to ConfigurationEvaluationState
instead of hanging the session.

app/services/cwmp/main_state_machine.ts

@@ -72,6 +72,16 @@ class DiscoveringParametersState extends DeviceState {
       return { response: await this.processNext(context) }
     }
 
+    // If CPE responded with a Fault, GPN is not supported — skip discovery
+    if (context.message && !context.message.success) {
+      logger.info(
+        { faultData: context.message.data },
+        '[DiscoveringParameters] GPN Fault received — marking as unsupported'
+      )
+      context.device.setGpnStatus('unsupported')
+      return { nextState: new ConfigurationEvaluationState(), response: '' }
+    }
+
     // Process response and continue
     if (this.parameterQueue.length > 0) {
       return { response: await this.processNext(context) }