nixpkgs' deno differs from the local toolchain, and deno fmt rules are version-specific, so CI's format step flagged CSS/HTML/SVG/Svelte files that are clean locally. Install a pinned Deno (DENO_VERSION) and put it on PATH so the checks — including the nested deno calls in `deno task ...` — match local. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>