Bug - Pressing Enter in editor inserts line break at wrong position and corrupts bullet list formatting

Requested by: @isaaclombardssw via YakShaver.ai cc: @isaaclombardssw, @lukecookssw, @MarcusIrmscherSSW, @kulesy, @JackDevAU

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Pain

Pressing Enter leaves the caret several lines from where it was placed and mangles the bullet list around it. The steps below do not reproduce this on current main. The missing precondition is a block that already contains hard line breaks. Real bug, wrong steps, so do not close it as works-fine.

Approach

Suspect is the break plugin, which drops the node attributes Slate's caret mapping walks. The hard-break fixes merged in August and September 2026 touched this same path and were never checked against this issue.

Acceptance Criteria

1. Enter in a block that already contains hard line breaks leaves the caret where it was placed
2. The bullet list keeps its structure after that Enter
3. Verified in a live browser editor, not a headless one

Reproduce Steps

1. Open TinaCMS
2. Navigate to an existing Markdown or MDX content item containing a bullet list
3. Place the cursor on a line above or within the list
4. Press Enter

Screenshot

Figure: Enter key creates misplaced line breaks and incorrect bullet formatting