The `@boneskull/typedoc-plugin-mermaid` creates both dark and light theme
variants of each diagram, each with identical marker IDs (e.g., `#arrowhead`).
When mermaid renders SVGs at runtime, lines reference `url(#arrowhead)`, but
the browser resolves this to the first match in document order — the hidden
dark-theme SVG — causing arrows to be invisible.
The fix removes dark-theme `<div class="mermaid dark">` elements at build time,
leaving only one SVG per diagram with unique marker IDs. A CSS filter
(`filter: invert(1) hue-rotate(180deg)`) handles dark mode styling instead.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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