[lexical-markdown] Bug Fix: don't prefix a newline when a selection starts below the first block

[luantaraschi]

Description

$convertSelectionToMarkdownString decides whether to prefix a block with \n by looking at the block's index among the root's children:

isNewlineDelimited &&
  i > 0 &&
  !isEmptyParagraph(child) &&
  !isEmptyParagraph(children[i - 1])

Unselected children emit nothing, so the index is not the position in the output. When the selection starts below the top of the document, the first block that does get emitted still has i > 0, and a newline is prefixed to it. The returned markdown then opens with a blank line.

With three paragraphs and a selection covering only the last two:

$convertSelectionToMarkdownString(TRANSFORMERS, $getSelection())
// '\nSecond\n\nThird', expected 'Second\n\nThird'

The separator now tracks the previously emitted block instead of the previous child. When every child is selected, the previously emitted block is children[i - 1], so nothing changes for the existing cases.

createMarkdownExport has the same shape but not the same bug: $exportTopLevelElements only returns null for a node that is neither an element nor a decorator, which a root child never is, so every child there contributes to the output.

Test plan

Before

FAIL packages/lexical-markdown/src/__tests__/unit/LexicalMarkdown.test.ts
  > $convertSelectionToMarkdownString
    > does not prefix a newline when the selection starts after the first block

AssertionError: expected '\nSecond\n\nThird' to be 'Second\n\nThird'

After

Test Files  1 passed (1)
     Tests  417 passed (417)

pnpm run prettier and pnpm run tsc are both clean.

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview	Aug 7, 2026 4:40pm
lexical-playground	Ready	Preview	Aug 7, 2026 4:40pm

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