fix(markdown): comprehensive improvements to markdown block/inline parsing and UI rendering

[Yashh56]

PR Description

Summary

This PR introduces a series of robust fixes to the Markdown parser and UI rendering engine. It addresses multiple edge cases in both block- and inline-Markdown parsing, ensuring that complex combinations—such as nested lists, blockquotes containing lists, and nested inline elements—are formatted precisely to specification.

It also resolves a UI styling conflict with spoiler elements.

Key Changes

1. Block-Level Parsing

• Nested Lists: Refactored indentation tracking (buildList stack) to accurately map indentation depths, ensuring nested lists are generated with the correct hierarchy rather than being flattened.

• Ordered Lists:

  • Updated the regex to support multi-digit markers (e.g., 10., 100.), which were previously failing to parse.
  • Restricted alphabetical lists to valid types (a, A, i, I), preventing arbitrary letters (e.g., Q.) from erroneously triggering list creation.
  • Fixed an editor fallback bug where malformed ordered lists would default to a - metadata attribute, accidentally converting them to unordered lists.

• Unordered Lists: Fixed getListType to properly recognize hyphens (-) alongside asterisks (*) as valid unordered list markers.

• Blockquotes: Enabled recursive parsing inside BlockQuoteRule, allowing internal block elements (such as lists or headings) to be formatted correctly within a quote rather than rendering as raw text.

2. Inline-Level Parsing

• Rule Precedence: Moved CodeRule into LeveledRules to fix regex precedence issues. This prevents inline code blocks from prematurely splitting strings, which previously broke outer syntax such as links or spoilers containing code.

• Escaped Characters: Added \[ and \] to INLINE_SEQUENCE_SET so that escaped square brackets are correctly unescaped and ignored by the link parser.

3. UI & Styling

• Spoiler Visibility: Fixed a styling conflict where child elements inside an unrevealed spoiler (such as <code /> blocks with distinct backgrounds/colors) remained visible.

  Used Vanilla Extract's globalStyle to apply opacity: 0 to all descendants of an unrevealed spoiler, ensuring everything is completely hidden until clicked.

Testing

• Verified blockquote recursive rendering.
• Verified nested unordered/ordered lists mapping to Slate editor states.
• Verified lists starting with double digits (e.g., 10. Foo).
• Verified invalid lists (e.g., Q. Foo) are gracefully parsed as regular paragraphs.
• Verified escaped brackets (\[bracket\]) render as raw text.
• Verified spoiler tags (||) properly mask inline <code /> blocks.

Close: #2845

[Yashh56]

Tested the changes with the following Markdown cases to verify nested lists, escaped brackets in links, inline code within links, blockquotes, and spoilers containing inline code:

- Foo
  - Bar
- Baz

[This is a link with a \[bracket\]](https://example.com)

[This is a link with `code`](https://example.com)

> #### The story of markdown
>
> Markdown is a thing.

||`hidden code`||

All of the above cases are rendering as expected. I’ve also attached a screenshot of the resulting output below.