[Bug]: Markdown file preview renders YAML frontmatter as a setext heading #23704

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open a project that has a Markdown file starting with YAML frontmatter, for example:

   ---
   type: Task
   title: Decide the joke source and Draft safety limits
   description: Settle where Jokes come from and what a Draft may never contain.
   status: draft
   task_status: ready
   blocked_by: []
   created: 2026-10-22
   ---
   
   # Decide the joke source and Draft safety limits

2. Open that file from the Files panel so it shows in the rendered Markdown preview.

Expected behavior

The frontmatter block is recognised as metadata. It is either hidden or shown as a small key/value table, the way GitHub, GitLab and Obsidian render it. The document starts at the # heading.

Actual behavior

The frontmatter is rendered as ordinary Markdown:

• The opening --- becomes a horizontal rule.
• All the YAML lines collapse into one paragraph (type: Task title: … created: 2026-10-22).
• The closing --- under that paragraph turns it into a setext H2.

So every file with frontmatter opens with a large bold run-on "heading" made of its metadata.

Impact

Minor bug or occasional failure

Version or commit

T3 Code (Beta) desktop 0.1.0

Environment

macOS 27 (Darwin 27.0.0), T3 Code desktop app

Workaround

Switch the file tab to source view, or open the file in an external editor.

Context

We keep project knowledge as Markdown files with YAML frontmatter, using the OKF v0.2 convention: every page carries type, title, description and status, and Task pages also carry Board fields such as task_status and blocked_by. Agents and humans read these files side by side in T3 Code. Frontmatter is also standard in Obsidian vaults, static-site generators and agent skill files (SKILL.md), so most Markdown in agent-driven repositories hits this.

A likely fix: enable frontmatter parsing in the Markdown preview (for example remark-frontmatter, if the preview uses remark/react-markdown), then hide the block or render it as a compact properties table.