FileUpload

pub fn buildFileUpload(scope: *ui.Scope, cx: *ui.Cx) anyerror!*ui.Node {
    const a = cx.allocator;
    const c = try col(cx, 12);
    const story = try cx.bindState(FileUploadStory, .{ .state = undefined });
    const fu = try ui.widgets.FileUpload(.{
        .width = 380,
        .on_browse = cx.on(FileUploadStory, story, FileUploadStory.browse),
    }, scope, cx);
    story.state = fu.state;
    fu.wrapper.meta.ownership.meta.test_id = "story.upload.wrapper";
    // 拖放 drop zone：e2e 用 dragAt 往这块矩形里注入 entered/dropped
    fu.state.drop_zone.meta.ownership.meta.test_id = "story.upload.dropzone";
    try c.appendChild(a, fu.wrapper);
    return c;
}