[richtext-lexical] Strikethrough/inline format carries into a manually-typed checklist ([x]) on the next line #18639

Describe the Bug

An inline format (strikethrough, and similarly any text format) applied to a line is carried into the next line's manually-typed checklist item ([x] markdown shortcut), even after the format has been toggled off. Inserting the checklist through the / slash menu does not have this problem.

Environment:

• payload: 3.84.1
• @payloadcms/richtext-lexical: 3.84.1
• bundled lexical / @lexical/markdown: 0.41.0
• BuildChromium (editor in dark theme, default features + FixedToolbarFeature)

Link to the code that reproduces this issue

https://github.com/riancintiyo/payload-strikethrough-repro.git

Reproduction Steps

Steps to reproduce

1. In a rich-text field, create strikethrough text using the markdown shortcut: strike.
2. Press Enter to start a new line.
3. Type a checklist manually with markdown: [x] Some task (space after ] triggers the checklist transform).

Actual: Some task is rendered struck through.
Expected: Some task is normal text.

Variants (help narrow it down)

• strike + Enter + / menu → Check box: ✅ not affected (expected, clean).
• Select text → apply strikethrough from the toolbar → Enter → toggle strikethrough off → type [x] Some task: ❌ still struck.
• So the difference is newline + manual [] checklist conversion vs. the / command. Toggling the format off does not help.

Root cause analysis

1. On Enter, Lexical copies the current selection's inline format onto the new paragraph — ParagraphNode.insertNewAfter (lexical@0.41.0, Lexical.dev.mjs:10006):
   newElement.setTextFormat(rangeSelection.format); // block.__textFormat = strikethrough
   A block's textFormat re-derives the selection format (Lexical.dev.mjs:7592), so the new line is struck at the block level.
2. Toggling the toolbar off on a collapsed caret only calls RangeSelection.toggleFormat() (:6502) — it flips selection.format but never clears the paragraph's __textFormat, so the strike returns on the next keystroke.
3. Payload's checklist markdown transformer re-parents the line's text nodes into a ListItemNode without resetting the format — @payloadcms/richtext-lexical/dist/features/lists/shared/markdown.js:27 (listReplace → listItem.append(...children)).
4. The / menu path fires INSERT_CHECK_LIST_COMMAND (fresh ListNode/ListItemNode with __textFormat = 0), which is why it's clean.
   Suggested fix
   In the checklist markdown transformer (listReplace), clear the inline format of the appended children (e.g. children.forEach(n => $isTextNode(n) && n.setFormat(0))), or clear the new block's textFormat right after insertNewAfter. Either keeps the fix scoped to the markdown-conversion path while leaving intentional Bold/Italic carry-over intact.
   Notes

• Likely also affects ordered/unordered lists and any element transformer on a freshly-created line, since the same listReplace path is shared.
• Possibly also reportable upstream to facebook/lexical (block-textFormat persistence across a format toggle), but the checklist behavior is reproducible from Payload's markdown transformer alone.

Which area(s) are affected?

plugin: richtext-lexical

Environment Info

Binaries:
  Node: 22.14.0
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  payload: 3.84.1
  next: 16.2.4
  @payloadcms/db-vercel-postgres: 3.84.1
  @payloadcms/drizzle: 3.84.1
  @payloadcms/graphql: 3.84.1
  @payloadcms/next/utilities: 3.84.1
  @payloadcms/plugin-cloud-storage: 3.84.1
  @payloadcms/richtext-lexical: 3.84.1
  @payloadcms/storage-s3: 3.84.1
  @payloadcms/translations: 3.84.1
  @payloadcms/ui/shared: 3.84.1
  react: 19.2.4
  react-dom: 19.2.4
Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Home
  Available memory (MB): 16152
  Available CPU cores: 8