Improve Dev Proxy API port conflict handling with helpful error messages

DevProxy/Commands/DevProxyCommand.cs

@@ -493,25 +493,34 @@ private async Task<int> InvokeAsync(InvocationContext context)
 
             return 0;
         }
-        catch (TaskCanceledException)
-        {
-            throw;
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "An error occurred while running Dev Proxy");
-            var inner = ex.InnerException;
-
-            while (inner is not null)
-            {
-                _logger.LogError(inner, "============ Inner exception ============");
-                inner = inner.InnerException;
-            }
-#if DEBUG
-            throw; // so debug tools go straight to the source of the exception when attached
-#else
-            return 1;
-#endif
+        catch (TaskCanceledException)
+        {
+            throw;
+        }
+        catch (IOException ex) when (ex.Message.Contains("Failed to bind to address", StringComparison.OrdinalIgnoreCase) && ex.Message.Contains($":{_proxyConfiguration.ApiPort}", StringComparison.OrdinalIgnoreCase))
+        {
+            _logger.LogError("Dev Proxy API port {ApiPort} is already in use.", _proxyConfiguration.ApiPort);
+            _logger.LogError("To resolve this issue:");
+            _logger.LogError("1. Add the 'apiPort' property to your configuration file and set it to a different port number");
+            _logger.LogError("2. If you're using Dev Proxy Toolkit, update the API port extension setting to match your custom port");
+            _logger.LogError("Example configuration: {{ \"apiPort\": 8898 }}");
+            return 1;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "An error occurred while running Dev Proxy");
+            var inner = ex.InnerException;
+
+            while (inner is not null)
+            {
+                _logger.LogError(inner, "============ Inner exception ============");
+                inner = inner.InnerException;
+            }
+#if DEBUG
+            throw; // so debug tools go straight to the source of the exception when attached
+#else
+            return 1;
+#endif
         }
     }