Fix isSubPath to allow filenames starting with ".."

internal/storage/local_test.go

@@ -128,3 +128,21 @@ func TestOpenMissingFile(t *testing.T) {
 		t.Errorf("expected 'not found on disk' error, got: %v", err)
 	}
 }
+
+func TestIsSubPath_SameDirectory(t *testing.T) {
+	if !isSubPath("/base", "/base") {
+		t.Error("isSubPath should return true when base == target")
+	}
+}
+
+func TestIsSubPath_ShortChildName(t *testing.T) {
+	if !isSubPath("/base", "/base/a") {
+		t.Error("isSubPath should return true for single-char child path")
+	}
+}
+
+func TestIsSubPath_DotDotPrefixFilename(t *testing.T) {
+	if !isSubPath("/base", "/base/..foo") {
+		t.Error("isSubPath should return true for filename starting with ..")
+	}
+}