fix(theme/CodeBlockRuntime): Render SSR fallback for CodeBlockRuntime to avoid first-paint empty DOM/CLS

[Copilot]

• Understand current CodeBlockRuntime rendering and SSR gap
• Run existing CodeBlockRuntime tests to establish baseline
• Implement SSR fallback to render initial code placeholder
• Add/update targeted tests to cover initial DOM rendering (SSG + no JS)
• Re-run relevant tests and verify behavior

Original prompt

CodeBlockRuntime 组件，现在遇到两个问题

1. 在 SSG 时，首屏没有 dom 信息
2. 缺少首屏，导致会触发 CLS

可以在首屏时，将 Code 放上去，即使没有高亮，作为占位

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[netlify]

✅ Deploy Preview for rspress-v2 ready!

Name	Link
🔨 Latest commit	e4a74f7
🔍 Latest deploy log	https://app.netlify.com/projects/rspress-v2/deploys/6942ab03cb3fba0008f458bc
😎 Deploy Preview	https://deploy-preview-2902--rspress-v2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ SoonIter
❌ Copilot
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions]

Rsdoctor Bundle Diff Analysis

📊 Quick Summary (Click to expand)

Project	Total Size	Change
web	14.9 MB	➡️ 302.0 B (0.0%)

📁 web

Path: website/doc_build/web/rsdoctor-data.json

📌 Baseline Commit: e86fde2df5 | PR: #2319

Metric	Current	Baseline	Change
📊 Total Size	14.9 MB	14.9 MB	302.0 B (0.0%)
📄 JavaScript	14.3 MB	14.3 MB	298.0 B (0.0%)
🎨 CSS	114.2 KB	114.2 KB	4.0 B (0.0%)
🌐 HTML	0 B	0 B	N/A
📁 Other Assets	512.5 KB	512.5 KB	0 B (0.0%)

📦 Download Diff Report: web Bundle Diff

Generated by Rsdoctor GitHub Action

[Copilot]

Pull request overview

This pull request adds server-side rendering (SSR) fallback support to the CodeBlockRuntime component to prevent empty DOM on first paint and avoid Cumulative Layout Shift (CLS) issues during static site generation.

Key Changes:

• Implemented a lightweight fallback that renders unhighlighted code immediately during SSR, preventing empty DOM until Shiki syntax highlighting completes
• Added explicit prop flow for wrapCode, lineNumbers, and button group properties through both fallback and highlighted rendering paths
• Extended E2E test coverage with a new test suite that verifies SSG output renders correctly with JavaScript disabled

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
packages/core/src/theme/components/CodeBlockRuntime/index.tsx	Added useMemo-based fallback rendering with SSR-compatible <pre><code> structure; restructured prop handling to explicitly pass through wrapCode and lineNumbers
packages/core/src/theme/components/CodeBlock/index.scss	Converted pixel units to rem units for improved accessibility and consistency (margins and padding)
e2e/fixtures/code-block-runtime/index.test.ts	Added new test suite for SSG scenario that verifies static HTML renders code content when JavaScript is disabled
scripts/dictionary.txt	Added 'domcontentloaded' to the spell-check dictionary for the new test code

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)