[Bug] Typing over a triple-clicked line above a task list or table detaches it, and Enter on a list then throws "Failed to execute 'insertBefore'"

Description

Triple-clicking a line directly above a task list or a table and typing a character removes that line on screen, but not from the document. The line's block stays in the editor's block tree with its element gone, so a later Enter, Enter at the end of a bullet list above it opens the "Unexpected renderer process error" dialog with NotFoundError: Failed to execute 'insertBefore' on 'Node'. This is one of the triggers behind #5035.

Steps to Reproduce

1. Create a file with:

   - one
   - two
   
   text
   
   - [ ] task
   

2. Open it in MarkText.
3. Triple-click text.
4. Type x.
5. Click at the end of two, press Enter, then press Enter again.

With a table in place of the task list (| a | b | / | - | - | / | 1 | 2 |), step 4 detaches the whole table instead.

Expected Behavior

x replaces text in the document and on screen. The second Enter turns the empty bullet into an empty paragraph below the list. No error.

Actual Behavior

• After step 4 the text line disappears and x shows up inside the task item, while the document (and the saved file) still says text.
• The second Enter in step 5 opens the "Unexpected renderer process error" dialog.
• On the same triple-click selection, before typing: copy puts nothing on the clipboard, and cut, Backspace, Delete, Enter and Cmd+B do nothing. The same happens above a math block or an HTML block.

Screenshots / Logs

NotFoundError: Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted is not a child of this node.
    at ScrollPage.insertBefore
    at ScrollPage.insertAfter
    at ParagraphContent._enterInListItem
    at ParagraphContent.enterHandler
    at ParagraphContent.keydownHandler

Operating System

macOS

MarkText Version

0.20.0-rc.3 (also reproduced on 0.20.0-rc.1 and the current develop branch)

OS Version

macOS 27.0 (arm64)

Reproducibility

• I can reliably reproduce this issue

Related

• #5035: the same crash; this is one of its triggers.
• #5389: typing over a triple-clicked line swallows the next block. Its task list and table variants are the first half of this bug.
• #5381 carried a fix for this before it was narrowed to the setext heading trigger.

Possible cause: Chromium ends a triple-click selection at offset 0 of the next block. A task list item starts with its checkbox and a table with its figure, so no content leaf holds that end, and TextSelection.getSelection() returns null. Every consumer then sees no selection: the keydown cross-block cut in packages/muya/src/clipboard/index.ts does nothing, copy has nothing to copy, and the typed key's native edit deletes the paragraph's element. Two fixes were prototyped: pulling the selection end back onto text inside a beforeinput handler, and normalizing the selection on selectionchange, which also makes copy, cut and Backspace work on it.