Preserve error chain in ErrorCollector.FormattedError for multi-error aggregation

pkg/workflow/error_aggregation_test.go

@@ -4,12 +4,21 @@ package workflow
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+type testFormattedErrorChainType struct {
+	message string
+}
+
+func (e *testFormattedErrorChainType) Error() string {
+	return e.message
+}
+
 func TestNewErrorCollector(t *testing.T) {
 	tests := []struct {
 		name     string
@@ -271,3 +280,21 @@ func TestErrorCollectorFormattedError(t *testing.T) {
 		})
 	}
 }
+
+func TestErrorCollectorFormattedError_PreservesErrorChain(t *testing.T) {
+	collector := NewErrorCollector(false)
+	sentinelErr := errors.New("sentinel")
+	typedErr := &testFormattedErrorChainType{message: "typed"}
+
+	require.NoError(t, collector.Add(fmt.Errorf("wrapped sentinel: %w", sentinelErr)), "Should collect wrapped sentinel error")
+	require.NoError(t, collector.Add(fmt.Errorf("wrapped typed: %w", typedErr)), "Should collect wrapped typed error")
+
+	result := collector.FormattedError("validation")
+	require.Error(t, result, "Should return formatted error")
+
+	require.ErrorIs(t, result, sentinelErr, "FormattedError should preserve errors.Is chain")
+
+	var extractedTypedErr *testFormattedErrorChainType
+	require.ErrorAs(t, result, &extractedTypedErr, "FormattedError should preserve errors.As chain")
+	assert.Equal(t, typedErr, extractedTypedErr, "errors.As should extract the wrapped typed error")
+}

pkg/workflow/workflow_errors.go

@@ -250,15 +250,8 @@ func (c *ErrorCollector) FormattedError(category string) error {
 		return c.errors[0]
 	}
 
-	// Build formatted error with count header
-	var sb strings.Builder
-	fmt.Fprintf(&sb, "Found %d %s errors:", len(c.errors), category)
-	for _, err := range c.errors {
-		sb.WriteString("\n  • ")
-		sb.WriteString(err.Error())
-	}
-
-	return fmt.Errorf("%s", sb.String())
+	header := fmt.Sprintf("Found %d %s errors:", len(c.errors), category)
+	return fmt.Errorf("%s\n%w", header, errors.Join(c.errors...))
 }
 
 var sharedWorkflowLog = logger.New("workflow:shared_workflow_error")