webapi: address DataTransfer review feedback

- DataTransferItem/DataTransferItemList/Iterator forward acquireRef/releaseRef
  to the owning DataTransfer, so its pooled arena outlives any JS-held wrapper
  (fixes a potential use-after-free when JS keeps an item/list/iterator alive
  past the DataTransfer).
- addItem reads strings straight into the persistent arena via
  toStringSliceWithAlloc, removing the intermediate call_arena copy.
- normalizeFormat uses std.ascii.allocLowerString instead of dupe + lowerString.
- setData: rename dup -> owned_data for clarity.

src/browser/webapi/DataTransfer.zig

@@ -98,8 +98,7 @@ fn normalizeFormat(arena: Allocator, format: []const u8) ![]const u8 {
     if (std.ascii.eqlIgnoreCase(format, "url")) {
         return "text/uri-list";
     }
-    const buf = try arena.dupe(u8, format);
-    return std.ascii.lowerString(buf, buf);
+    return std.ascii.allocLowerString(arena, format);
 }
 
 pub fn getData(self: *const DataTransfer, format: []const u8, frame: *Frame) ![]const u8 {
@@ -114,15 +113,15 @@ pub fn getData(self: *const DataTransfer, format: []const u8, frame: *Frame) ![]
 
 pub fn setData(self: *DataTransfer, format: []const u8, data: []const u8) !void {
     const norm = try normalizeFormat(self._arena, format);
-    const dup = try self._arena.dupe(u8, data);
+    const owned_data = try self._arena.dupe(u8, data);
     for (self._items.items) |it| {
         if (it._kind == .string and std.mem.eql(u8, it._type, norm)) {
-            it._payload = .{ .string = dup };
+            it._payload = .{ .string = owned_data };
             return;
         }
     }
     const it = try self._arena.create(DataTransferItem);
-    it.* = .{ ._kind = .string, ._type = norm, ._payload = .{ .string = dup } };
+    it.* = .{ ._data_transfer = self, ._kind = .string, ._type = norm, ._payload = .{ .string = owned_data } };
     try self._items.append(self._arena, it);
 }
 
@@ -159,11 +158,10 @@ pub fn addItem(self: *DataTransfer, data: js.Value, type_: ?[]const u8, frame: *
         return try self.addFileItem(file, frame);
     } else |_| {}
 
-    const s = try data.toZig([]const u8);
+    const owned_data = try data.toStringSliceWithAlloc(self._arena);
     const norm = try normalizeFormat(self._arena, type_ orelse "");
-    const dup = try self._arena.dupe(u8, s);
     const it = try self._arena.create(DataTransferItem);
-    it.* = .{ ._kind = .string, ._type = norm, ._payload = .{ .string = dup } };
+    it.* = .{ ._data_transfer = self, ._kind = .string, ._type = norm, ._payload = .{ .string = owned_data } };
     try self._items.append(self._arena, it);
     return it;
 }
@@ -171,7 +169,7 @@ pub fn addItem(self: *DataTransfer, data: js.Value, type_: ?[]const u8, frame: *
 fn addFileItem(self: *DataTransfer, file: *File, frame: *Frame) !*DataTransferItem {
     file._proto.acquireRef();
     const it = try self._arena.create(DataTransferItem);
-    it.* = .{ ._kind = .file, ._type = file._proto.getType(), ._payload = .{ .file = file } };
+    it.* = .{ ._data_transfer = self, ._kind = .file, ._type = file._proto.getType(), ._payload = .{ .file = file } };
     try self._items.append(self._arena, it);
     try self.rebuildFiles(frame);
     return it;

src/browser/webapi/DataTransferItem.zig

@@ -22,6 +22,8 @@ const lp = @import("lightpanda");
 const js = @import("../js/js.zig");
 
 const File = @import("File.zig");
+const Page = @import("../Page.zig");
+const DataTransfer = @import("DataTransfer.zig");
 
 const log = lp.log;
 
@@ -30,6 +32,10 @@ const DataTransferItem = @This();
 
 pub const Kind = enum { string, file };
 
+// The owning DataTransfer. The item lives in that DataTransfer's arena and is
+// handed to JS, so it forwards acquireRef/releaseRef to keep the arena alive as
+// long as JS holds the item.
+_data_transfer: *DataTransfer,
 _kind: Kind,
 // For string items: the normalized format (e.g. "text/plain").
 // For file items: the File's MIME type.
@@ -41,6 +47,14 @@ pub const Payload = union(Kind) {
     file: *File,
 };
 
+pub fn acquireRef(self: *DataTransferItem) void {
+    self._data_transfer.acquireRef();
+}
+
+pub fn releaseRef(self: *DataTransferItem, page: *Page) void {
+    self._data_transfer.releaseRef(page);
+}
+
 pub fn getKind(self: *const DataTransferItem) []const u8 {
     return switch (self._kind) {
         .string => "string",

src/browser/webapi/DataTransferItemList.zig

@@ -18,6 +18,7 @@
 
 const js = @import("../js/js.zig");
 const Frame = @import("../Frame.zig");
+const Page = @import("../Page.zig");
 
 const DataTransfer = @import("DataTransfer.zig");
 const DataTransferItem = @import("DataTransferItem.zig");
@@ -30,6 +31,14 @@ const DataTransferItemList = @This();
 
 _data_transfer: *DataTransfer,
 
+pub fn acquireRef(self: *DataTransferItemList) void {
+    self._data_transfer.acquireRef();
+}
+
+pub fn releaseRef(self: *DataTransferItemList, page: *Page) void {
+    self._data_transfer.releaseRef(page);
+}
+
 pub fn getLength(self: *const DataTransferItemList) u32 {
     return @intCast(self._data_transfer._items.items.len);
 }
@@ -69,6 +78,14 @@ pub const Iterator = GenericIterator(struct {
     index: u32,
     list: *DataTransferItemList,
 
+    pub fn acquireRef(self: *@This()) void {
+        self.list.acquireRef();
+    }
+
+    pub fn releaseRef(self: *@This(), page: *Page) void {
+        self.list.releaseRef(page);
+    }
+
     pub fn next(self: *@This(), _: *const js.Execution) ?*DataTransferItem {
         const index = self.index;
         const it = self.list.item(index) orelse return null;