[lexical-markdown] Bug Fix: Preserve headings when typing list shortcuts

[StevenPDang]

This PR prevents Markdown list shortcuts from replacing an existing HeadingNode when a list marker is typed at the beginning of the heading. Previously, markers such as 1. matched the list transformer based only on the block’s leading text, replacing the heading with a ListNode/ListItemNode and recording the transformation in history.

List shortcut replacement now checks whether the source block is a heading. When it is, the transformer declines the replacement, preserving both the HeadingNode and the typed marker as normal heading text.

What changed

packages/lexical-markdown/src/MarkdownTransformers.ts — updates the shared list replacement function to skip shortcut
driven transformations when the parent block is a HeadingNode. Markdown import behavior is unchanged.

packages/lexical-markdown/src/tests/unit/LexicalMarkdown.test.ts — adds parameterized regression coverage for the
ordered marker 1. and unordered markers - , * , and + . Each case verifies directly that the block remains a
HeadingNode and retains the complete typed text.

Backwards compatibility

No public APIs, types, transformer signatures, or serialized formats are changed.

Markdown import behavior remains unchanged. Shortcut behavior for paragraphs and other non-heading blocks is
preserved.

Test plan

  pnpm run test-unit packages/lexical-markdown/src/__tests__/unit/LexicalMarkdown.test.ts — 416 pass
  prettier — clean
  eslint — clean
  git diff --check — clean

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview	Jul 26, 2026 10:57pm
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