fix: persist empty POST in TR-069 trace when CPE uses a new TCP port

When a CPE sends an empty POST (polling) on a new TCP connection, the
remoteKey (IP:port) differs from the one registered during Inform.
Add StateMachineManager.getHashIdForRemoteIp() to find the device by
IP alone as a fallback, so cwmpDeviceId is resolved and the exchange
is properly stored in the trace (cwmpMethod: Empty, dashed arrow).

app/services/cwmp/state_machine_manager.ts

@@ -248,6 +248,31 @@ export class StateMachineManager extends EventEmitter {
     }
   }
 
+  /**
+   * Fallback lookup: returns the hash identifier for any active device whose
+   * last known remote IP matches the given IP (ignoring port).
+   * Used when a CPE opens a new TCP connection for an empty POST and the
+   * exact remoteKey (IP:port) is not in the map.
+   */
+  getHashIdForRemoteIp(remoteIp: string): string | undefined {
+    for (const [key, deviceKeyJson] of this.remoteToDevice.entries()) {
+      const keyIp = key.split(':').slice(0, -1).join(':') // strip port (handles IPv6 too)
+      if (keyIp !== remoteIp) continue
+      try {
+        const deviceId = JSON.parse(deviceKeyJson)
+        return getDeviceHashIdentifier({
+          manufacturer: deviceId.manufacturer ?? '',
+          oui: deviceId.oui,
+          productClass: deviceId.productClass,
+          serialNumber: deviceId.serialNumber,
+        })
+      } catch {
+        return undefined
+      }
+    }
+    return undefined
+  }
+
   /**
    * Ensure session is bound when TCP connection changes
    */