[examples] Undo restores only part of a replaced partial text selection

[wudidewo12]

Description

In the Plain Text example, replacing a dragged partial text selection and then pressing Cmd+Z does not restore the full original selected text locally. The live reference restores the selected text correctly.

This is separate from the full Cmd+A replacement undo issue because this reproduction uses a normal partial text selection inside one paragraph.

Recording

Screenshots attached below:

Local actual behavior:

Live reference expected behavior:

Video attached below:
[optional; screenshots should be enough unless the drag-select/type/undo sequence is unclear]

Sandbox

No standalone sandbox. Reproduced in the Slate examples site.

Local reproduction URL:

http://localhost:3100/examples/plaintext

Reference URL:

https://www.slatejs.org/examples/plaintext

Additional confirmed scope:

This issue is not limited to the original Plain Text reproduction. The same partial-selection replacement undo problem has now been reproduced across multiple Slate examples, including:

• examples/plaintext
• examples/inlines
• examples/styling
• examples/code-highlighting

In each case, selecting part of the editor text, typing replacement text, and pressing Cmd+Z does not fully restore the original selected text locally. The live reference restores the selected text correctly.

In examples/inlines, selecting links, typing URLs, then pressing Cmd+Z leaves localhost as There are two ways to add U...; selecting existing link text hyperlink, typing wiki, then pressing Cmd+Z leaves localhost link text as w. The live reference restores the original selected text in both checks.

In examples/styling, selecting the word using, typing changed, then pressing Cmd+Z leaves localhost with only c restored in place of the selected word. The live reference restores using.

Styling steps checked:

1. Open http://localhost:3100/examples/styling.
2. Select the word using in either styled editor.
3. Type changed.
4. Press Cmd+Z.
5. Compare with https://www.slatejs.org/examples/styling.

Steps

To reproduce the behavior:

1. Go to http://localhost:3100/examples/plaintext.
2. Drag-select the word plain , including the trailing space, from the sentence This is editable plain text, just like a <textarea>!.
3. Type simple.
4. Press Cmd+Z.
5. Repeat the same steps on https://www.slatejs.org/examples/plaintext.

Expectation

After pressing Cmd+Z, the editor should restore the original text:

This is editable plain text, just like a <textarea>!

Actual behavior

On localhost, after pressing Cmd+Z, the original selected text is not restored. The editor becomes:

This is editable stext, just like a <textarea>!

The live reference restores the original plain selection.

Environment

• Local URL: http://localhost:3100/examples/plaintext
• Reference URL: https://www.slatejs.org/examples/plaintext
• Local branch/commit: v2, ce2bd6c6
• Browser: Chrome
• OS: macOS
• Local app setup: Slate examples site served locally with bun serve

Impact

This breaks a normal text editing undo workflow. Replacing a partial text selection and undoing can leave corrupted text locally instead of restoring the original selected text.

[zbeyens]

🟡 80-94% confidence

Phase	🧪 Tests	🌐 Browser
Reproduced	✅ Issue screenshots/transcripts show partial selection undo restoring only part of the text	✅ Plain Text flow identified
Verified	🟢 Plain Text partial-selection replacement undo row is green on current v2 07d79634	⚠️ Extra listed examples still need route-specific proof

🌐 Browser Check

• Open http://localhost:3100/examples/plaintext.
• Select part of the sentence, such as plain .
• Type replacement text, such as simple.
• Press Cmd+Z.
• Confirm the original selected text is restored.

✅ Outcome

• Current v2 passes the Plain Text partial-selection replacement undo proof.
• The verified row restores the original selected text/range.

⚠️ Caveat

• The issue also names inlines, styling, and code-highlighting. This pass did not run browser rows for those extra routes, so I am leaving this open until that broader scope is confirmed.

🏗️ Design

• Chosen owner: expanded selection replacement plus history restore.
• Why not quick patch: the current Plain Text proof is already green.
• Why not broader change: the issue needs exact cross-route browser evidence before full closure.

🧪 Verified

• cd /Users/zbeyens/git/slate-v2 && PLAYWRIGHT_RETRIES=0 PLAYWRIGHT_BASE_URL=http://localhost:3100 bun playwright playwright/integration/examples/plaintext.test.ts playwright/integration/examples/mentions.test.ts playwright/integration/examples/paste-html.test.ts playwright/integration/examples/iframe.test.ts --project=chromium --grep "keyboard undo restores caret after middle-line typing|keyboard undo restores partial selected text replacement|keyboard undo restores select-all replacement content|copies and pastes a selected mention without crashing|cuts a selected mention without crashing|pastes copied rendered Slate content as an internal fragment before HTML import|applies parent toolbar formatting to selected iframe text"
• cd /Users/zbeyens/git/slate-v2 && bun check