Fix servicebus error propagation

core/Azure.Mcp.Core/tests/Azure.Mcp.Core.UnitTests/Areas/Server/Commands/ToolLoading/NamespaceToolLoaderTests.cs

@@ -419,6 +419,39 @@ public async Task CallToolHandler_ThreadSafeLazyLoading()
         });
     }
 
+    [Fact]
+    public async Task CallToolHandler_PreservesSpecificErrorMessageForMissingParameters()
+    {
+        // Arrange
+        var loader = new NamespaceToolLoader(_commandFactory, _options, _serviceProvider, _logger);
+        // Use subscription list command which requires --subscription or AZURE_SUBSCRIPTION_ID
+        var toolName = "subscription";
+
+        // Create request without required subscription parameter
+        var request = CreateCallToolRequest(toolName, new Dictionary<string, object?>
+        {
+            ["command"] = "list",
+            ["parameters"] = new Dictionary<string, object?>()
+        });
+
+        // Act
+        var result = await loader.CallToolHandler(request, TestContext.Current.CancellationToken);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.True(result.IsError);
+
+        var textContent = result.Content[0] as TextContentBlock;
+        Assert.NotNull(textContent);
+
+        // Verify the specific error message is preserved (not replaced with generic message)
+        Assert.Contains("Missing Required options:", textContent.Text);
+
+        // Verify the command spec guidance is still included
+        Assert.Contains("Review the following command spec", textContent.Text);
+        Assert.Contains("Command Spec:", textContent.Text);
+    }
+
     [Fact]
     public async Task DisposeAsync_ClearsCaches()
     {
@@ -556,6 +589,35 @@ await Assert.ThrowsAsync<ArgumentNullException>(async () =>
             await options.Handlers.ElicitationHandler.Invoke(null!, TestContext.Current.CancellationToken));
     }
 
+    [Fact]
+    public async Task CallToolHandler_WithMissingRequiredOptions_PreservesSpecificErrorMessage()
+    {
+        // Arrange
+        // Service Bus commands require --subscription parameter
+        // When calling without it, we should get a specific error message, not a generic one
+        const string command = "servicebus_namespace_list";
+        var args = new Dictionary<string, object>(); // Missing required --subscription parameter
+
+        var request = CreateCallToolRequest(command, args);
+
+        // Act
+        var response = await _loader.CallToolHandler(request, TestContext.Current.CancellationToken);
+
+        // Assert
+        Assert.NotNull(response);
+        Assert.True(response.IsError);
+        Assert.Single(response.Content);
+
+        var textContent = response.Content[0] as TextContent;
+        Assert.NotNull(textContent);
+
+        // Verify the specific error message is preserved (not the generic "missing required parameters")
+        Assert.Contains("Missing Required options: --subscription", textContent.Text);
+
+        // Verify it still includes the command spec guidance
+        Assert.Contains("Review the following command spec", textContent.Text);
+    }
+
     // Helper methods
 
     private string GetFirstAvailableNamespace()

core/Azure.Mcp.Core/tests/Azure.Mcp.Core.UnitTests/Areas/Server/Commands/ToolLoading/ServerToolLoaderTests.cs

@@ -136,4 +136,47 @@ public async Task ListToolsHandler_WithRealRegistryDiscovery_ReturnsExpectedStru
             Assert.True(tool.InputSchema.ValueKind != JsonValueKind.Undefined, "InputSchema should be defined");
         }
     }
+
+    [Fact]
+    public async Task CallToolHandler_PreservesSpecificErrorMessageForMissingParameters()
+    {
+        // Arrange - use real RegistryDiscoveryStrategy
+        var serviceProvider = new ServiceCollection().AddLogging().BuildServiceProvider();
+        var loggerFactory = serviceProvider.GetRequiredService<ILoggerFactory>();
+        var serviceStartOptions = Microsoft.Extensions.Options.Options.Create(new ServiceStartOptions());
+        var toolLoaderOptions = Microsoft.Extensions.Options.Options.Create(new ToolLoaderOptions());
+        var discoveryLogger = loggerFactory.CreateLogger<RegistryDiscoveryStrategy>();
+        var discoveryStrategy = RegistryDiscoveryStrategyHelper.CreateStrategy(serviceStartOptions.Value, discoveryLogger);
+        var logger = loggerFactory.CreateLogger<ServerToolLoader>();
+
+        var toolLoader = new ServerToolLoader(discoveryStrategy, toolLoaderOptions, logger);
+
+        // Create request for documentation tool with missing required parameters
+        var request = CreateCallToolRequest("documentation",
+            new Dictionary<string, JsonElement>
+            {
+                { "command", JsonDocument.Parse("\"microsoft_docs_search\"").RootElement },
+                // Missing 'question' parameter which is required
+                { "parameters", JsonDocument.Parse("{}").RootElement }
+            });
+
+        // Act
+        var result = await toolLoader.CallToolHandler(request, TestContext.Current.CancellationToken);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.NotNull(result.Content);
+        Assert.NotEmpty(result.Content);
+
+        var textContent = result.Content[0] as TextContentBlock;
+        Assert.NotNull(textContent);
+
+        // Verify the specific error message is preserved (not replaced with generic message)
+        // Should contain "Missing required options:" or similar specific error, not generic "missing required parameters"
+        Assert.Contains("Missing", textContent.Text);
+
+        // Verify the command spec guidance is still included
+        Assert.Contains("Review the following command spec", textContent.Text);
+        Assert.Contains("Command Spec:", textContent.Text);
+    }
 }

core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/NamespaceToolLoader.cs

@@ -380,13 +380,19 @@ private async Task<CallToolResult> InvokeChildToolAsync(
                 var childToolSpecJson = GetChildToolJson(request, namespaceName, command);
 
                 _logger.LogWarning("Namespace {Namespace} command {Command} requires additional parameters.", namespaceName, command);
+
+                // Extract the specific error message from the response
+                var errorMessage = string.IsNullOrEmpty(commandResponse.Message)
+                    ? $"The '{command}' command is missing required parameters."
+                    : commandResponse.Message;
+
                 var finalResponse = new CallToolResult
                 {
                     Content =
                     [
                         new TextContentBlock {
                                 Text = $"""
-                                    The '{command}' command is missing required parameters.
+                                    {errorMessage}
 
                                     - Review the following command spec and identify the required arguments from the input schema.
                                     - Omit any arguments that are not required or do not apply to your use case.

core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/ServerToolLoader.cs

@@ -283,7 +283,7 @@ private async Task<CallToolResult> InvokeChildToolAsync(RequestContext<CallToolR
                         [
                             new TextContentBlock {
                                     Text = $"""
-                                        The '{command}' command is missing required parameters.
+                                        {textContent.Text}
 
                                         - Review the following command spec and identify the required arguments from the input schema.
                                         - Omit any arguments that are not required or do not apply to your use case.