Upgrade kit/ to Svelte 5, SvelteKit 2, Vite 7, Tailwind 4, ESLint 10

[mishig25]

What

Upgrades the whole kit/ toolchain: Svelte 4 → 5.56, SvelteKit 1.20 → 2.68, Vite 4 → 7.3, Tailwind 3 → 4.1, ESLint 8 (.eslintrc) → 10 (flat config), latest Prettier plugins, svelte-check 4, mdsvex 0.12.

Highlights

svelteKitCustomClient/ is gone 🎉

The ~2,100-line fork of SvelteKit's client.js (which existed to make shorthand doc URLs like /docs/lib/page partial-load instead of full-reload) is replaced by ~40 lines of public API:

• src/hooks.js — SvelteKit 2's reroute universal hook, expanding shorthand paths to the built library/version/lang route.
• A capture-phase click listener in +layout.svelte that canonicalizes shorthand anchor hrefs before kit's router reads them (needed because kit's external-URL check runs before reroute for URLs outside paths.base).
• DOCS_LIBRARY/DOCS_VERSION/DOCS_LANGUAGE are injected via Vite define instead of a generated file inside node_modules, so the custom-svelte-client npm script is gone too. No more re-porting the fork on every kit upgrade.

One visible behavior change: clicking a shorthand link now shows the canonical full URL (/docs/lib/main/en/page) in the address bar instead of keeping the shorthand. Navigation is still client-side (verified, see below).

Other adaptations

• postprocess.js: Svelte 5 no longer emits <!-- HEAD_svelte-*_START --> markers, so the hf:doc:metadata tag is extracted directly; the moon-landing line-1 contract (line 1 = charset + metadata meta, rest = page component) is preserved, including moving the head <link> kit 2 renders inline back to line 2.
• Tailwind 4 via @tailwindcss/postcss; app.css rewritten to v4 syntax (@utility instead of @variants, ! suffix, slash-opacity instead of --tw-bg-opacity) plus the documented v3-compat base styles. The legacy tailwind.config.cjs theme is kept via @config; plugins load via @plugin. Utility class names in markup are untouched (prod CSS is emptied and comes from the hub build).
• Tailwind v4 auto-detects sources honoring .gitignore, which excludes src/routes (doc pages are pasted there at build time) — added @source "./routes" so doc-builder preview keeps its styles.
• cheerio 1.x final dropped its default export → namespace import in the mdsvex preprocessor.
• @huggingface/inference stays lock-pinned at 4.13.15: newer patches shrink the InferenceProvider type union and break InferenceSnippet.svelte; bump deliberately via npm run update-inference-providers.

Verification

Baseline accelerate e2e build (same as accelerate_doc.yml) was run on the old stack first, then compared against the upgraded build:

• 48/48 pages: identical hf:doc:metadata, hrefs, image srcs, heading ids, code-block counts. Only diffs: Svelte 5 trims some trailing whitespace in text nodes (invisible), and Python <object object at 0x…> addresses in docstring signatures that differ between any two runs.
• Browser smoke test (playwright + Chrome, run against both builds): hydration works, full-path links SPA-navigate, shorthand links SPA-navigate with correct content, HfOptions tabs interactive, no new console errors vs baseline.
• svelte-check: 0 errors · prettier --check: clean · npm ci && npm run build exercised through the full doc-builder python pipeline.

Note: npx eslint . reports 39 pre-existing violations (no-shadow, no-explicit-any, non-null assertions) that the old .eslintrc also declared but never enforced in CI — left untouched here to keep the diff reviewable; happy to fix in a follow-up.

🤖 Generated with Claude Code