feat(markdown): render frontmatter in file previews

[tarik02]

What Changed

Backports pingdotgg/t3code#8202.

• Render valid leading YAML frontmatter as a metadata table in web, desktop, and mobile file previews.
• Show scalar arrays as pills and nested values as YAML.
• Preserve invalid, unclosed, and non-mapping frontmatter as raw Markdown.
• Keep task-list edits mapped to the original file offsets.

Why

Markdown previews currently show frontmatter as raw delimiters and YAML. This matches GitHub's metadata-table presentation while keeping parsing shared and client rendering local.

UI Changes

Before:

After:

Verification

• vp i, including the lockfile supply-chain check
• Formatting check for all 8 changed files
• Targeted lint for all changed TypeScript and TSX files
• Client runtime, web, and mobile typechecks
• Backport patch-id matches upstream PR #8202

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for the UI changes
• A video is not applicable because this does not change animation or interaction

Made with GPT-5.6 Sol using the Codex harness in T3 Code.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 37acf335e1

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• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Preserve large integer values in YAML frontmatter

When a mapping contains an integer outside JavaScript's safe range, the YAML transformation converts it to a number and Schema.Json accepts the already-rounded result. For example, id: 9007199254740993 is displayed as 9007199254740992 on every preview surface, silently changing identifier-like metadata. Preserve the scalar lexeme or otherwise parse integers without losing precision before building the display value.

Useful? React with 👍 / 👎.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	12.1 KiB	12.1 KiB	−5 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	5.8 KiB	5.8 KiB	−6 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+1 B (+0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.5 KiB	55.5 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	12.2 KiB	12.2 KiB	−36 B (−0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	5.8 KiB	5.8 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−35 B (−0.5%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.4 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: 04932a5 · PR result: 37acf33 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 84.1 KiB
• Claude decoded thread snapshot: 84.5 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.