fix: re-enable LAN after stopping SD card logging

src/Daqifi.Core.Tests/Device/SdCard/SdCardOperationsTests.cs

@@ -197,10 +197,29 @@ public async Task StopSdCardLoggingAsync_SendsCorrectCommands()
 
             // Assert
             var sentCommands = device.SentMessages.Select(m => m.Data).ToList();
-            Assert.Equal(3, sentCommands.Count);
+            Assert.Equal(4, sentCommands.Count);
             Assert.Equal("SYSTem:StopStreamData", sentCommands[0]);
             Assert.Equal("SYSTem:STORage:SD:ENAble 0", sentCommands[1]);
             Assert.Equal("SYSTem:STReam:INTerface 0", sentCommands[2]); // Restore USB
+            Assert.Equal("SYSTem:COMMunicate:LAN:ENAbled 1", sentCommands[3]); // Re-enable LAN
+        }
+
+        [Fact]
+        public async Task StopSdCardLoggingAsync_SendsStopCommandEvenWhenIsStreamingIsFalse()
+        {
+            // Arrange - simulate stale IsStreaming state (see issue #118)
+            var device = new TestableSdCardStreamingDevice("TestDevice");
+            device.Connect();
+            await device.StartSdCardLoggingAsync("test.bin");
+            device.StopStreaming(); // Sets IsStreaming = false
+            device.SentMessages.Clear();
+
+            // Act
+            await device.StopSdCardLoggingAsync();
+
+            // Assert - stop command should still be sent defensively
+            var sentCommands = device.SentMessages.Select(m => m.Data).ToList();
+            Assert.Contains("SYSTem:StopStreamData", sentCommands);
         }
 
         [Fact]

src/Daqifi.Core/Device/DaqifiStreamingDevice.cs

@@ -452,7 +452,10 @@ public Task StopSdCardLoggingAsync(CancellationToken cancellationToken = default
 
             cancellationToken.ThrowIfCancellationRequested();
 
-            StopStreaming();
+            // Defensive: always send stop command even if IsStreaming is stale (see issue #118)
+            Send(ScpiMessageProducer.StopStreaming);
+            IsStreaming = false;
+
             Send(ScpiMessageProducer.DisableStorageSd);
 
             // Restore stream interface to USB so subsequent non-SD operations work.
@@ -461,6 +464,10 @@ public Task StopSdCardLoggingAsync(CancellationToken cancellationToken = default
                 Send(ScpiMessageProducer.SetStreamInterface(StreamInterface.Usb));
             }
 
+            // Re-enable LAN interface. StartSdCardLoggingAsync disables LAN because
+            // the SD card and WiFi/LAN share the SPI bus on the hardware.
+            Send(ScpiMessageProducer.EnableNetworkLan);
+
             _isLoggingToSdCard = false;
 
             return Task.CompletedTask;