[Feature] Add opt-in task checkbox interaction with host write-back / 支持可选任务勾选与宿主回写 #7

English

Use case

In a local-file Markdown editor, clicking - [ ] / - [x] in the reading/preview pane should be able to request a source change through the host's document/undo pipeline. Vex currently supports this interaction and would need an equivalent integration point when adopting StreamMark.

Reviewed: TKCode.StreamMark.Avalonia 0.1.0-alpha.23, Avalonia 12.1.4, .NET 10.

Current behavior

The parser supports task lists. In the reviewed implementation, ListItemBlockView draws the marker using CheckboxRun, whose source describes it as read-only. There is no public host write-back event identified in this path. This is a source/API inspection finding, not a pointer-input test result.

Sources: ContainerViews.cs, InlineRuns.cs.

Requested improvement

Add opt-in task interaction, keeping the current read-only default:

• a click/keyboard action emits a host request containing entry/document version, task-marker source range, current state and requested state;
• the host accepts/rejects the request and performs the actual Markdown edit, undo grouping and persistence;
• StreamMark does not write files or mutate an immutable snapshot on its own;
• interaction is disabled or version-checked when the source is incomplete/stale.

A public callback/event is sufficient; no full editor is required.

Acceptance criteria

• Nested tasks, ordered/unordered lists and duplicate task labels identify the correct source marker.
• Changing [ ] ↔ [x] preserves unrelated text, indentation and CRLF.
• Read-only hosts produce no edit request; rejected requests leave the rendered state unchanged.
• The host can apply one undoable edit and reject an outdated request by version.
• Keyboard activation and accessibility state are considered, and clicking task text can still select text normally.

中文

使用场景与当前边界

本地 Markdown 编辑器通常支持在阅读/预览界面点击任务框，再通过宿主文档与撤销系统回写原文。Vex 已有该交互，迁移到 StreamMark 时需要对应入口。

当前解析器支持任务列表，但所检查的实现使用只读 CheckboxRun 绘制任务框，尚未在这条调用路径中发现公开的宿主回写事件。此结论来自源码/API 检查，不是实际鼠标点击测试。

建议

提供默认关闭的任务交互功能。点击或键盘操作时，向宿主发送包含文档/条目版本、任务标记源码范围、当前与目标状态的请求。由宿主接受或拒绝，并负责修改原文、记录撤销和保存；StreamMark 不自行写文件，也不把派生快照当作可变原文。

源码未完成或版本过期时应禁用交互或校验版本。公开事件/回调即可，不要求内置完整编辑器。

验收

嵌套、不同列表类型和重复文本均能定位正确任务；只修改目标状态，保留缩进、CRLF 和其他原文；只读模式不发请求，拒绝请求不改变勾选状态；宿主可作为单次操作撤销并拒绝过期请求；考虑键盘和无障碍，同时保留任务正文的正常选区行为。