fix(card-editor): confirming an empty new card creates nothing

PLAN 5.4 says an unchanged confirmation writes nothing, but the shortcut
applied only to existing cards, so OK on a blank new-card editor added an
empty card. A new card with no title, content or tags is now not created.

YKanBan.Tests/ViewModels/BoardViewModelTests.cs

@@ -225,6 +225,48 @@ public class BoardViewModelTests
         Assert.AreEqual(100, fixture.Repository.GetCard(card.Id)!.UpdatedAt);
     }
 
+    [TestMethod]
+    public void ConfirmingAnEmptyNewCardCreatesNothing()
+    {
+        using var fixture = new Fixture();
+        ColumnModel column = fixture.Repository.AddColumn("A", "");
+        var editor = CardEditorDialogViewModel.ForNewCard(fixture.Repository, fixture.Dialogs, column.Id, confirmDiscard: true);
+        bool? closedWith = null;
+        editor.CloseRequested += (_, result) => closedWith = result;
+        editor.CardTitle = "draft";
+        editor.CardTitle = "";
+
+        editor.ConfirmCommand.Execute(null);
+
+        Assert.IsTrue(closedWith);
+        Assert.IsNull(editor.SavedCard);
+        Assert.AreEqual(0, fixture.Repository.GetCards().Count);
+    }
+
+    [TestMethod]
+    public async Task NewCardWithOnlyATagIsCreated()
+    {
+        using var fixture = new Fixture();
+        ColumnModel column = fixture.Repository.AddColumn("A", "");
+        TagModel bug = fixture.Repository.AddTag("bug", new RgbColor(255, 0, 0), "");
+        var editor = CardEditorDialogViewModel.ForNewCard(fixture.Repository, fixture.Dialogs, column.Id, confirmDiscard: true);
+        fixture.Dialogs.Script = dialog =>
+        {
+            if (dialog is TagPickerDialogViewModel picker)
+            {
+                picker.PickCommand.Execute(picker.FilteredTags.Single());
+            }
+            return Task.CompletedTask;
+        };
+
+        await editor.AddTagCommand.ExecuteAsync(null);
+        editor.ConfirmCommand.Execute(null);
+
+        CardModel card = fixture.Repository.GetCards().Single();
+        Assert.AreEqual("", card.Title);
+        Assert.AreEqual(bug.Id, card.Tags.Single().Id);
+    }
+
     [TestMethod]
     public async Task DirtyCancelAsksAndStaysOpenWhenDeclined()
     {

YKanBan/ViewModels/Dialogs/CardEditorDialogViewModel.cs

@@ -12,8 +12,8 @@ namespace YKanBan.ViewModels.Dialogs;
 /// The card editor — one unit of work. Title, content and the tag assignment
 /// are edited in memory and written together in a single transaction on
 /// confirmation; cancelling writes nothing about the card or its assignment.
-/// Confirming an existing card without effective changes writes nothing and
-/// keeps its timestamps. The only immediate write is the creation of a new tag
+/// Confirming without effective changes writes nothing: an existing card keeps
+/// its timestamps, and a new card left empty is not created. The only immediate write is the creation of a new tag
 /// in the nested tag picker (see <see cref="TagPickerDialogViewModel"/>).
 /// </summary>
 public sealed partial class CardEditorDialogViewModel : DialogViewModelBase
@@ -113,7 +113,8 @@ public sealed partial class CardEditorDialogViewModel : DialogViewModelBase
     public ObservableCollection<TagBadgeViewModel> Tags { get; }
 
     /// <summary>
-    /// Gets the card written on confirmation; <see langword="null"/> until then.
+    /// Gets the card written on confirmation; <see langword="null"/> until then,
+    /// and after confirming a new card that was left empty.
     /// </summary>
     public CardModel? SavedCard { get; private set; }
 
@@ -182,13 +183,13 @@ public sealed partial class CardEditorDialogViewModel : DialogViewModelBase
     private void RemoveTag(TagBadgeViewModel tag) => Tags.Remove(tag);
 
     /// <summary>
-    /// Writes the card in one transaction and closes; an unchanged existing card
-    /// is not written at all.
+    /// Writes the card in one transaction and closes; an unchanged card is not
+    /// written at all, so a new card left empty is not created.
     /// </summary>
     [RelayCommand]
     private void Confirm()
     {
-        if (_existing is not null && !IsDirty)
+        if (!IsDirty)
         {
             SavedCard = _existing;
             Close(true);

docs/ACCEPTANCE.md

@@ -64,6 +64,7 @@
 - [ ] 新建列、编辑列（标题 + 描述）；空标题、重名（含仅大小写不同，如 `Done` / `done`）→ 模态内提示错误，模态不关、输入保留
 - [ ] 删除列：确认框提示将删除 N 张卡片；确认后列与卡片一并删除
 - [ ] 新建卡片、点击卡片编辑：标题可空；内容多行；`#id` / 创建时间 / 修改时间只读显示（新建时不显示）
+- [ ] 新建卡片什么都不填（标题、内容、标签均空）直接确认：不产生卡片；只加一个标签再确认：产生无标题卡片
 - [ ] 编辑确认但内容未变 → 修改时间不变；改动后确认 → 修改时间刷新
 - [ ] 有未保存改动时取消或点标题栏关闭 → 丢弃确认（开关开启时）
 - [ ] 卡片菜单"移动到列"：卡片移动，修改时间**不**变

docs/PLAN.md

@@ -16,7 +16,7 @@
 - 网络共享明确不支持；命令行参数边界；macOS 无参启动行为写入文档（§2.3、§4.1、附录）
 - 补充：导出转义规则、卡片列表虚拟化、模态窗口 FlowDirection、`Resources` 类名使用规则、CI osx-x64 运行器（§5、§7、§8）
 - 依赖：Avalonia 11.3.6 → 11.3.22，Semi.Avalonia 11.2.1.10 → 11.3.22（§7）
-- 实现回补：搜索括号嵌套上限 64 层、单个表达式至多 256 个原子，空短语、短语紧贴文本、`key:` 后空白均为非法（§6.1、§6.2）；导出表格单元格转义 `\`、默认文件名剔除非法字符（§5.8）；初始化中途锁冲突进锁冲突页、数据库文件缺失不静默新建（§4.4）；app.json 读不出 / 备份写不出 / 退出写盘失败均不阻断启动与退出（§4.3）
+- 实现回补：搜索括号嵌套上限 64 层、单个表达式至多 256 个原子，空短语、短语紧贴文本、`key:` 后空白均为非法（§6.1、§6.2）；导出表格单元格转义 `\`、默认文件名剔除非法字符（§5.8）；初始化中途锁冲突进锁冲突页、数据库文件缺失不静默新建（§4.4）；app.json 读不出 / 备份写不出 / 退出写盘失败均不阻断启动与退出（§4.3）；主题下拉选中即预览、取消恢复（§5.6）；空白新卡片确认不创建（§5.4）
 - 里程碑：标注 M0–M4 已完成，新增 **M4R（v1.9 回补）**（§9）
 
 ## 1. 项目概述
@@ -201,7 +201,7 @@ card_tags: (card_id, tag_id) 复合主键，双向 ON DELETE CASCADE
 - 字段：标题（可空，空串 = 无标题）、内容（多行）、标签区、只读 `#id` / 创建时间 / 修改时间（新增时未生成则不显示）
 - 底部：确认（当前数据一次性写入数据库）/ 取消（丢弃更改）
 - 编辑对话框是一个工作单元：确认时一次性落库（单事务，见 §3），取消不产生任何卡片/指派写入；其余操作（删除、移动等）仍即时写库
-- 确认时内容无变化 → 不写库、不刷新时间戳
+- 确认时内容无变化 → 不写库、不刷新时间戳；新建卡片时即标题、内容、标签均为空 → 确认不创建卡片（等同取消）
 - 标签指派：编辑模态标签区显示已指派标签（各带 × 移除），"添加标签"按钮弹**嵌套模态** = 已有标签搜索/列表 + 新建标签入口，选中即添加，可反复打开继续添加下一个
 - **例外**：嵌套模态中新建的标签**立即写入 `tags` 表**（标签是全局实体）；外层编辑取消时仅丢弃指派关系，新建的标签保留（与"tag 永不自动清理"一致）