refactor: improve whitespace validation and add comprehensive test coverage

Address feedback from @gemini-code-assist[bot] review:

1. Enhanced validation in parseStringArgs():
   - Use strings.TrimSpace() to reject arguments consisting solely of whitespace
   - Prevents creating nodes with whitespace-only paths
   - Maintains preservation of intentional whitespace in valid arguments

2. Added comprehensive test cases for whitespace handling:
   - Whitespace-only arguments (should be rejected)
   - Multiple empty string arguments (should be rejected)
   - Arguments with leading/trailing spaces (should be preserved)
   - Mixed whitespace scenarios

This improves robustness while maintaining backward compatibility and
the core functionality of handling unquoted paths with spaces.

Author: raravena80

pkg/modelfile/parser/args_parser.go

@@ -33,7 +33,7 @@ func parseStringArgs(args []string, start, end int) (Node, error) {
 	// Join all arguments with spaces to handle unquoted file paths with spaces
 	joined := strings.Join(args, " ")
 
-	if joined == "" {
+	if strings.TrimSpace(joined) == "" {
 		return nil, errors.New("empty args")
 	}
 

pkg/modelfile/parser/args_parser_test.go

@@ -38,6 +38,12 @@ func TestParseStringArgs(t *testing.T) {
 		// Additional test cases for spaces in file paths
 		{[]string{"path", "with", "spaces/file.json"}, 11, 12, false, "path with spaces/file.json"},
 		{[]string{"example", "workflows_Wan2.1/image_to_video_wan_480p_example.json"}, 13, 14, false, "example workflows_Wan2.1/image_to_video_wan_480p_example.json"},
+		// Test cases for whitespace handling
+		{[]string{" "}, 15, 16, true, ""},                                               // Whitespace-only argument should be rejected
+		{[]string{"", ""}, 17, 18, true, ""},                                            // Multiple empty string arguments should be rejected
+		{[]string{" a "}, 19, 20, false, " a "},                                         // Arguments with leading/trailing spaces should be preserved
+		{[]string{"  ", "   "}, 21, 22, true, ""},                                       // Multiple whitespace-only arguments should be rejected
+		{[]string{" path ", "with", " spaces "}, 23, 24, false, " path  with  spaces "}, // Mixed whitespace should be preserved
 	}
 
 	assert := assert.New(t)