fix: address Copilot PR #407 review comments

- Fix comment in testutil/utils.go to reflect actual panic behavior instead of fallback values
- Improve aa_sender validation error message to include invalid value for better debugging
- Simplify template resolution error message by moving explanation to log field
- Enhance hyphen validation log message with specific guidance about valid variable paths
- Update LoadSecretsForImmediateExecution comment to clarify user-level secrets limitation

These changes improve code clarity, debugging capabilities, and user guidance
based on GitHub Copilot feedback in PR #407.

Author: weilicious

core/taskengine/vm.go

@@ -1704,7 +1704,7 @@ func (v *VM) preprocessTextWithVariableMapping(text string) string {
 		// - Variable names: settings.uniswap-pool (should be settings.uniswap_pool)
 		if isSimpleVariablePath(expr) && strings.Contains(expr, "-") {
 			if v.logger != nil {
-				v.logger.Warn("Template variable path contains invalid character (hyphen)", "expression", expr)
+				v.logger.Warn("Template variable path contains invalid character (hyphen) - use snake_case for simple variable paths", "expression", expr, "help", "Hyphens are only invalid in simple variable paths like 'settings.field-name'. Use 'settings.field_name' instead. Hyphens are allowed in complex expressions, string literals, and array indexing.")
 			}
 			result = result[:start] + "undefined" + result[end+2:]
 			continue

core/taskengine/vm_runner_contract_write.go

@@ -146,7 +146,7 @@ func (r *ContractWriteProcessor) executeMethodCall(
 			return &avsproto.ContractWriteNode_MethodResult{
 				MethodName: methodCall.MethodName,
 				Success:    false,
-				Error:      "aa_sender variable is set but invalid - must be a non-empty hex address string",
+				Error:      fmt.Sprintf("aa_sender variable is set but invalid - must be a non-empty hex address string, got: %v", aaSenderVar),
 			}
 		}
 	} else {
@@ -171,12 +171,13 @@ func (r *ContractWriteProcessor) executeMethodCall(
 				r.vm.logger.Error("❌ CONTRACT WRITE - Template variable failed to resolve",
 					"method", methodCall.MethodName,
 					"original_param", param,
-					"resolved_param", resolvedMethodParams[i])
+					"resolved_param", resolvedMethodParams[i],
+					"explanation", "This may be due to an undefined variable, incorrect template syntax, or unsupported variable names (e.g., variables with hyphens are not supported; use snake_case such as 'recipient_address' instead of 'recipient-address').")
 			}
 			return &avsproto.ContractWriteNode_MethodResult{
 				MethodName: methodCall.MethodName,
 				Success:    false,
-				Error:      fmt.Sprintf("template variable resolution failed in parameter %d: '%s' resolved to '%s'. This may be due to an undefined variable, incorrect template syntax, or unsupported variable names (e.g., variables with hyphens are not supported; use snake_case such as 'recipient_address' instead of 'recipient-address').", i, param, resolvedMethodParams[i]),
+				Error:      fmt.Sprintf("template variable resolution failed in parameter %d: '%s' resolved to '%s'", i, param, resolvedMethodParams[i]),
 			}
 		}
 	}