feat: implement comprehensive error handling and validation

- Added DSL configuration validation with clear error messages
- Implemented robust error handling for model processing
- Added helpful suggestions for configuration mistakes
- Created logging and debugging support

Completes Prompt 9 of implementation plan

Author: ianbotsf

plugins/custom-sdk-build/src/main/kotlin/aws/sdk/kotlin/gradle/customsdk/CustomSdkBuildExtension.kt

@@ -72,14 +72,44 @@ open class CustomSdkBuildExtension(private val project: Project) {
      * Throws an exception if the configuration is invalid.
      */
     internal fun validate() {
-        if (serviceConfigurations.isEmpty()) {
-            throw IllegalStateException("No services configured. Please configure at least one service.")
-        }
-        
-        serviceConfigurations.forEach { (serviceName, config) ->
-            if (config.selectedOperations.isEmpty()) {
-                throw IllegalStateException("No operations selected for service '$serviceName'. Please select at least one operation.")
+        try {
+            if (serviceConfigurations.isEmpty()) {
+                throw IllegalStateException(
+                    "No services configured for custom SDK generation. " +
+                    "Add at least one service configuration using the DSL:\n" +
+                    "awsCustomSdkBuild {\n" +
+                    "    s3 {\n" +
+                    "        operations(S3Operation.GetObject, S3Operation.PutObject)\n" +
+                    "    }\n" +
+                    "}"
+                )
+            }
+            
+            serviceConfigurations.forEach { (serviceName, config) ->
+                if (config.selectedOperations.isEmpty()) {
+                    throw IllegalStateException(
+                        "No operations selected for service '$serviceName'. " +
+                        "Add operations to your service configuration:\n" +
+                        "$serviceName {\n" +
+                        "    operations(/* operation constants */)\n" +
+                        "}"
+                    )
+                }
+                
+                // Check for duplicate operations
+                val duplicates = config.selectedOperations.groupingBy { it.shapeId }.eachCount().filter { it.value > 1 }
+                if (duplicates.isNotEmpty()) {
+                    project.logger.warn("Service '$serviceName' has duplicate operations: ${duplicates.keys}")
+                }
             }
+            
+            val totalOperations = serviceConfigurations.values.sumOf { it.selectedOperations.size }
+            project.logger.info("Extension validation passed: $totalOperations operations across ${serviceConfigurations.size} services")
+            
+        } catch (e: Exception) {
+            project.logger.error("Extension validation failed: ${e.message}")
+            ErrorHandling.suggestRecoveryActions(e, project.logger)
+            throw e
         }
     }
 

plugins/custom-sdk-build/src/main/kotlin/aws/sdk/kotlin/gradle/customsdk/CustomSdkBuildPlugin.kt

@@ -64,6 +64,9 @@ class CustomSdkBuildPlugin : Plugin<Project> {
             // Validate the extension configuration
             extension.validate()
 
+            // Perform comprehensive validation
+            validateConfiguration(project, extension)
+            
             // Log the selected operations for debugging
             val selectedOperations = extension.getSelectedOperations()
             project.logger.info("Custom SDK configuration:")
@@ -153,6 +156,33 @@ class CustomSdkBuildPlugin : Plugin<Project> {
         project.logger.info("Build optimizations configured for custom SDK generation")
     }
 
+    /**
+     * Validate the plugin configuration comprehensively.
+     */
+    private fun validateConfiguration(project: Project, extension: CustomSdkBuildExtension) {
+        try {
+            val selectedOperations = extension.getSelectedOperations()
+            val packageName = "aws.sdk.kotlin.services.custom" // Default package name
+            val packageVersion = project.version.toString()
+            
+            val validationResult = ValidationEngine.validateConfiguration(
+                project, selectedOperations, packageName, packageVersion
+            )
+            
+            // Log validation results
+            ValidationEngine.logValidationResults(project.logger, validationResult)
+            
+            // Throw exception if validation failed
+            if (!validationResult.isValid) {
+                ValidationEngine.throwValidationException(validationResult)
+            }
+            
+        } catch (e: Exception) {
+            ErrorHandling.suggestRecoveryActions(e, project.logger)
+            throw e
+        }
+    }
+    
     /**
      * Create placeholder model files for demonstration.
      * In a real implementation, these would be the actual AWS service models.