building-code-displays

---

name: building-code-displays user-invocable: false description: Build marketing-grade code displays for the Musher marketing site -- split-panel code-then-output layouts, CSS-only syntax highlighting, tabbed views, and terminal chrome. Use when implementing IA Section 3 (Mechanism), building code blocks, creating terminal demos, highlighting YAML/CLI output, or adding copy buttons to code. Triggered by: code display, code block, syntax highlighting, code-then-output, split panel code, terminal chrome, YAML highlight, CLI output, code snippet, tabbed code, multi-language code, mechanism section code, bundle yaml, pipeline yaml, marketing code. allowed-tools: Read, Write, Edit, Grep, Glob

Building Marketing Code Displays

Purpose

Build code display components for the marketing site without external syntax highlighting dependencies. The IA's Mechanism section (Section 3) requires code-then-output split panels showing YAML config and CLI output. This skill covers the full taxonomy of code displays and how to build each one.

Source Documents

• IA Section 3: /workspace/docs/marketing/information-architecture.md -- code-then-output layout pattern, content slot definitions
• Wireframe Copy: /workspace/docs/marketing/wireframe-copy.md -- exact YAML and CLI output content for bundle and pipeline code blocks
• Design Tokens: /workspace/apps/marketing-site/src/app.css -- @theme colors for syntax highlighting
• Existing CodeSnippet: apps/marketing-site/src/lib/components/CodeSnippet.svelte -- reference for code block with copy button
• Existing Terminal: apps/marketing-site/src/lib/components/InteractiveTerminal.svelte -- reference for terminal chrome pattern

Code Display Taxonomy

1. Static Code Snippet

Single code block with language label and copy button. Already implemented as CodeSnippet.svelte.

Use for: Standalone code examples, install commands.

2. Code-Then-Output Split (Primary -- IA Section 3)

Side-by-side or stacked panels: config on left, CLI output on right.

Use for: Mechanism section showing bundle YAML + musher bundle apply output, pipeline YAML + musher pipeline run output.

3. Tabbed Multi-File View

Multiple files shown via tab switching -- only one visible at a time.

Use for: When showing related files (e.g., bundle.yaml + pipeline.yaml in a tabbed interface).

4. Interactive Terminal

Animated terminal with typewriter effect and state transitions. Already implemented as InteractiveTerminal.svelte.

Use for: Hero section demo.

Code-Then-Output Split Panel

This is the primary pattern needed for IA Section 3.

Layout Structure

<div class="grid gap-4 lg:grid-cols-2">
  <!-- Left panel: Configuration file -->
  <div class="code-panel">
    <div class="code-chrome">
      <span class="filename">bundle.yaml</span>
      <CopyButton code={bundleYaml} />
    </div>
    <pre class="code-body"><code>{@html highlightYaml(bundleYaml)}</code></pre>
  </div>

  <!-- Right panel: CLI output -->
  <div class="code-panel">
    <div class="code-chrome terminal">
      <div class="terminal-dots">
        <span class="dot-red"></span>
        <span class="dot-yellow"></span>
        <span class="dot-green"></span>
      </div>
      <span class="filename">output</span>
    </div>
    <pre class="code-body"><code>{@html highlightCliOutput(cliOutput)}</code></pre>
  </div>
</div>

Responsive Behavior

• Desktop (lg+): grid-cols-2 -- side by side
• Mobile (<lg): stacked vertically, config on top, output below
• Both panels have equal visual weight -- same height via min-h or grid stretching

Chrome Pattern

The code panel chrome matches existing CodeSnippet.svelte and InteractiveTerminal.svelte:

<!-- Config file chrome -->
<div class="bg-surface-04/50 border-border-subtle flex items-center justify-between border-b px-4 py-2">
  <span class="text-label text-text-tertiary font-mono">{filename}</span>
  <CopyButton {code} />
</div>

<!-- Terminal output chrome -->
<div class="bg-surface-04/50 border-border-subtle flex items-center gap-2 border-b px-4 py-2">
  <div class="flex items-center gap-1.5">
    <div class="bg-signal-error h-2.5 w-2.5 rounded-full"></div>
    <div class="bg-signal-warning h-2.5 w-2.5 rounded-full"></div>
    <div class="bg-signal-success h-2.5 w-2.5 rounded-full"></div>
  </div>
  <span class="text-label text-text-tertiary font-mono ml-2">output</span>
</div>

Panel Styling

<!-- Outer panel wrapper -->
<div class="bg-surface-02 border-border-subtle shadow-panel overflow-hidden rounded-lg border">
  <!-- Chrome header (above) -->
  <!-- Code body -->
  <pre class="overflow-x-auto p-4 leading-relaxed"><code class="text-data font-mono">{@html highlighted}</code></pre>
</div>

CSS-Only Syntax Highlighting

Use design token colors for syntax highlighting. No external dependencies (no Shiki, no Prism, no highlight.js).

Color Mapping

YAML Token	Token Color	Tailwind Class	CSS Variable
Keys	text-signal-action	color: var(--color-signal-action)	#4589ff
String values	text-signal-success	color: var(--color-signal-success)	#42be65
Comments	text-text-tertiary	color: var(--color-text-tertiary)	#8d8d8d
Booleans/numbers	text-signal-warning	color: var(--color-signal-warning)	#ff832b
Punctuation (:, -)	text-text-secondary	color: var(--color-text-secondary)	#c6c6c6
Plain text	text-text-primary	color: var(--color-text-primary)	#f4f4f4

CLI Token	Token Color	Tailwind Class
Command prompt ($)	text-signal-action	#4589ff
Command name	text-text-primary	#f4f4f4
Flags (--repo)	text-signal-action	#4589ff
Status labels ([OK], Done.)	text-signal-success	#42be65
Indented output	text-text-secondary	#c6c6c6
Timing (14.2s)	text-signal-warning	#ff832b

Highlighting Functions

Implement highlighting as pure functions that return HTML strings with <span> tags:

function highlightYaml(code: string): string {
  return code
    .split('\n')
    .map((line) => {
      // Comments
      if (line.trimStart().startsWith('#')) {
        return `<span style="color: var(--color-text-tertiary)">${escapeHtml(line)}</span>`;
      }

      // Key: value pairs
      const keyMatch = line.match(/^(\s*)([\w-]+)(:)(.*)/);
      if (keyMatch) {
        const [, indent, key, colon, value] = keyMatch;
        const highlightedValue = highlightYamlValue(value.trim());
        return `${indent}<span style="color: var(--color-signal-action)">${escapeHtml(key)}</span><span style="color: var(--color-text-secondary)">${colon}</span> ${highlightedValue}`;
      }

      // List items
      const listMatch = line.match(/^(\s*)(- )(.*)/);
      if (listMatch) {
        const [, indent, dash, value] = listMatch;
        return `${indent}<span style="color: var(--color-text-secondary)">${dash}</span>${highlightYamlValue(value)}`;
      }

      return escapeHtml(line);
    })
    .join('\n');
}

function highlightYamlValue(value: string): string {
  if (!value) return '';

  // Quoted strings
  if (/^["'].*["']$/.test(value)) {
    return `<span style="color: var(--color-signal-success)">${escapeHtml(value)}</span>`;
  }

  // Booleans and numbers
  if (/^(true|false|\d+(\.\d+)?)$/.test(value)) {
    return `<span style="color: var(--color-signal-warning)">${escapeHtml(value)}</span>`;
  }

  // Plain values
  return `<span style="color: var(--color-text-primary)">${escapeHtml(value)}</span>`;
}

function highlightCliOutput(output: string): string {
  return output
    .split('\n')
    .map((line) => {
      // Command prompt lines
      if (line.startsWith('$ ')) {
        const cmd = line.slice(2);
        return `<span style="color: var(--color-signal-action)">$</span> <span style="color: var(--color-text-primary)">${escapeHtml(cmd)}</span>`;
      }

      // Status lines with success indicators
      if (/\b(Done|complete|completed|OK)\b/i.test(line)) {
        return `<span style="color: var(--color-signal-success)">${escapeHtml(line)}</span>`;
      }

      // Indented output
      if (line.startsWith('  ')) {
        // Highlight timing values
        const withTiming = escapeHtml(line).replace(
          /(\d+\.?\d*s)/g,
          '<span style="color: var(--color-signal-warning)">$1</span>'
        );
        return `<span style="color: var(--color-text-secondary)">${withTiming}</span>`;
      }

      return `<span style="color: var(--color-text-secondary)">${escapeHtml(line)}</span>`;
    })
    .join('\n');
}

function escapeHtml(text: string): string {
  return text
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;');
}

Important: Always escape HTML before inserting into {@html} to prevent XSS. The escapeHtml function must run before any <span> wrapping.

Using {@html} Safely

The highlighting functions produce trusted HTML from hardcoded IA content. This is safe because:

1. The input is static wireframe copy, not user input
2. All values are escaped via escapeHtml() before span-wrapping
3. The {@html} directive is used only for the pre-formatted code content

Tabbed Multi-File View

For showing multiple related files with tab switching:

<script lang="ts">
  interface Tab {
    label: string;
    filename: string;
    code: string;
    language: string;
  }

  interface Props {
    tabs: Tab[];
  }

  let { tabs }: Props = $props();
  let activeIndex = $state(0);
</script>

<div class="bg-surface-02 border-border-subtle shadow-panel overflow-hidden rounded-lg border">
  <!-- Tab bar -->
  <div class="bg-surface-04/50 border-border-subtle flex border-b">
    {#each tabs as tab, i}
      <button
        type="button"
        onclick={() => activeIndex = i}
        class="text-label px-4 py-2 font-mono transition-colors duration-fast
          {i === activeIndex
            ? 'text-text-primary border-b-2 border-signal-action bg-surface-02'
            : 'text-text-tertiary hover:text-text-secondary'}"
      >
        {tab.filename}
      </button>
    {/each}
  </div>

  <!-- Active panel -->
  <pre class="overflow-x-auto p-4 leading-relaxed"><code class="text-data font-mono">{@html highlight(tabs[activeIndex])}</code></pre>
</div>

IA Section 3 Content

The wireframe copy specifies exact YAML and CLI content. Here are the content slots to implement:

Bundle Code Block

Left panel (bundle.yaml):

name: code-review
agent: claude-code
allowed_tools:
  - read_file
  - edit_file
  - run_terminal_cmd
rules:
  - "Review for correctness, not style"
  - "Flag security issues as blocking"

Right panel (CLI output):

$ musher bundle apply --repo my-org/api
Applying bundle 'code-review' to my-org/api...
  Agent: claude-code
  Rules: 2 applied
  Tools: 3 allowed
  Done. Agent config written to .musher/bundles/code-review.yaml

Pipeline Code Block

Left panel (pipeline.yaml):

trigger:
  event: pull_request.opened
  source: github
job:
  bundle: code-review
  retry:
    attempts: 3
    backoff: exponential

Right panel (CLI output):

$ musher pipeline run --event pr-opened-42
Event received: pull_request.opened #42
Dispatching job: code-review
  Attempt 1/3... running
  Agent: claude-code
  Status: completed (14.2s)
Pipeline complete.

Copy Button Integration

Reuse the existing CopyButton.svelte pattern from CodeSnippet.svelte:

<script lang="ts">
  interface Props {
    code: string;
  }

  let { code }: Props = $props();
  let copied = $state(false);

  async function copy() {
    await navigator.clipboard.writeText(code);
    copied = true;
    setTimeout(() => (copied = false), 2000);
  }
</script>

<button
  type="button"
  onclick={copy}
  class="text-label text-text-tertiary hover:text-text-primary flex items-center gap-1 transition-colors duration-fast"
>
  {#if copied}
    <svg class="text-signal-success h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
      <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M5 13l4 4L19 7" />
    </svg>
    <span>Copied!</span>
  {:else}
    <svg class="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
      <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 16H6a2 2 0 01-2-2V6a2 2 0 012-2h8a2 2 0 012 2v2m-6 12h8a2 2 0 002-2v-8a2 2 0 00-2-2h-8a2 2 0 00-2 2v8a2 2 0 002 2z" />
    </svg>
    <span>Copy</span>
  {/if}
</button>

Or import the existing CopyButton from $lib/components/CopyButton.svelte.

Typography in Code Blocks

• Font: font-mono (JetBrains Mono from @theme)
• Size: text-data (13px/20px) for code content
• Line height: leading-relaxed (1.625) for readability in code blocks
• Chrome labels: text-label (11px/16px) with font-mono
• Tab size: 2 spaces (standard for YAML)

Anti-Patterns

DO NOT	DO
Install Shiki, Prism, or highlight.js	Use CSS-only highlighting with design token colors
Use <SyntaxHighlighter> from React	Build highlighting as Svelte-native pure functions
Use colors outside the token system	Map syntax tokens to --color-signal-* and --color-text-*
Highlight every token with regex	Keep it simple -- keys, values, comments, prompts are enough
Hard-code hex values in highlighting	Use var(--color-*) CSS variables for all colors
Use dangerouslySetInnerHTML	Use Svelte's {@html} with proper escaping
Auto-detect language	Explicitly pass language/content type per panel

Related Skills

• scaffolding-sections -- how Mechanism section fits into the overall section scaffold
• animating-scroll-reveals -- optional scroll reveal for code blocks appearing on scroll
• auditing-design-compliance -- verify code displays use correct tokens