fix(chrome): validate attribute name in unknown-prefix branch

A selector like `foo]:has(*),body[x:value` previously produced
[foo]:has(*),body[x="..."], a syntactically valid CSS selector that
escaped the attribute match and selected `body`. Reject anything that
isn't a plain HTML attribute name.

internal/driver/chrome/translate.go

@@ -3,10 +3,16 @@ package chrome
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"strings"
 	"unicode/utf8"
 )
 
+// attrNamePattern matches HTML attribute names that are safe to drop into a
+// CSS attribute selector without escaping. This avoids selectors like
+// `foo]:has(*),body[x="..."]` that would escape the intended match.
+var attrNamePattern = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9_-]*$`)
+
 // TranslateStringSelector converts a legacy string selector ("id:foo",
 // "descPrefix:bar") into a CSS selector or XPath expression usable from the
 // chrome driver's TapSelector fallback path. The boolean return is true when
@@ -41,6 +47,9 @@ func TranslateStringSelector(selector string) (string, bool, error) {
 	case "placeholder", "placeholderValue", "hintText":
 		return `[placeholder="` + cssEscape(value) + `"]`, false, nil
 	default:
+		if !attrNamePattern.MatchString(kind) {
+			return "", false, fmt.Errorf("unsafe selector prefix %q", kind)
+		}
 		return `[` + kind + `="` + cssEscape(value) + `"]`, false, nil
 	}
 }

internal/driver/chrome/translate_test.go

@@ -64,6 +64,21 @@ func TestTranslateStringSelector_RejectsMissingPrefix(t *testing.T) {
 	}
 }
 
+func TestTranslateStringSelector_RejectsUnsafePrefix(t *testing.T) {
+	cases := []string{
+		`foo]:has(*),body[x:value`,
+		`x y:value`,
+		`x"y:value`,
+		`*:value`,
+		`(:value`,
+	}
+	for _, selector := range cases {
+		if _, _, err := TranslateStringSelector(selector); err == nil {
+			t.Errorf("%q: expected error for unsafe prefix", selector)
+		}
+	}
+}
+
 func TestCSSEscape_ControlCharactersAndNUL(t *testing.T) {
 	cases := []struct {
 		name  string