fix(storage-walker): keep <br/> inside list items as a hard line break

[pchuri]

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Description

Fixes #242. In storage → markdown, <br/> inside a list item became a space. The walker emitted \n, and the item's inline whitespace collapse (added in #239) then erased it.

While the walker is inside whitespace-collapsed inline content (list items, table cells, task bodies), <br/> now emits a private-use HARD_BREAK sentinel (U+E003) that survives the collapse. The outermost such context resolves it:

Context	Storage	Markdown	Back to storage
List item	<ul><li>line1<br/>line2</li></ul>	- line1\ line2	<li>line1<br /> line2</li>
Task body	…<ac:task-body>a<br/>b</ac:task-body>…	- [ ] a\ b	<li>[ ] a<br /> b</li>
Table cell	<td>a<br/>b</td>	| a<br>b |	<td><p>a<br />b</p></td>

• List items and task bodies use a CommonMark backslash hard break, with the continuation indented to the content column via LIST_INDENT. A trailing-two-space break would be stripped by cleanupOutsideFence. Continuation lines that CommonMark would otherwise parse as a new block are backslash-escaped: - , * , + , 1. , 2) , # , >, a backtick or tilde fence, ---, ===, * * *, and GFM table delimiter rows such as --- | ---. An odd run of trailing backslashes before a break (C:\temp\) gets one more \ so it stays literal and the break survives. Inline syntax such as **bold** or a code span is left alone.
• Table cells use inline <br>, because GFM rows cannot span lines. markdownToStorage already normalizes <br> to <br /> ([BUG] Markdown line breaks generate invalid XHTML <br> instead of <br /> (fails on Confluence On-Premise) #210). Lists and tasks nested in a cell leave the sentinel for the cell to resolve.
• Unchanged:
  • Top-level <br/> still emits \n, which is a soft break. This is the same as main and out of scope for this PR.
  • Blocks inside a list item (blockquote, callout) behave as before.
  • <br/> inside <code> stays a space, since a code span cannot hold a line break.
• Sentinel escaping: literal U+E003 in user content is reversibly escaped in decodeEntities, like U+E000/U+E001/U+E002 (QUOTE_MARK, fix(storage-walker): keep code blocks inside blockquotes and callouts byte-exact #249). Task bodies use the shared list-item path from fix(storage-walker): preserve nested task lists in storage → markdown #245, so their breaks go through the same code.

Important

Behavior change (release notes): this affects every <br/> inside a table cell, not just ones in list items. That includes header cells and <p>, headings, blockquotes, panels, lists, tasks, links and <pre> inside cells, as well as tables nested in lists. Cells previously rendered those breaks as a space and now render them as inline <br>, which round-trips to <br />. For example, | > a > b | becomes | > a<br>b |.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

npx jest: 1453/1453 passed (after merging current main). npx eslint lib tests: clean. The new #242 suite in tests/macro-converter.test.js asserts exact output and markdown → storage → markdown round trips. 27 of its cases fail on main.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A

Additional Context

• The parity fixture 07-tables.expected.md changes intentionally: line one line two becomes line one<br>line two.
• lib/html-to-markdown.js is a separate converter and still renders <br> as a space in list items and table cells. That is a follow-up.

[github-actions]

🎉 This PR is included in version 2.25.8 🎉

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• npm package (@latest dist-tag)
• GitHub release

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