Upgrade the library build to Rollup 4 and TypeScript 5

[spaceninja]

Overview

Upgrades the library build toolchain: rollup 2 → 4, rollup-plugin-dts 4 → 6, @rollup/plugin-terser 0.4 → 1, @rollup/plugin-babel 6 → 7, @rollup/plugin-node-resolve 13 → 16, and TypeScript 4.9 → 5.9. These six travel together — rollup-plugin-dts 6 requires rollup ^3 || ^4, and its older 4.x line caps TypeScript below 5 — so splitting them further would leave the tree unresolvable.

No build code changed. gulpfile.js/tasks/build-scripts.js was already using the plain Rollup JS API with the modern scoped plugin packages, so all six majors were drop-in. The diff is 12 lines of package.json plus the lockfile.

The published UMD bundles get substantially smaller.sky-nav.ts imports the generated design-token module for three values, and rollup 2 emitted all 97KB of it. Rollup 4 tree-shakes the object literal down to the reachable leaves, so dist/cloudfour-patterns.js drops 116KB → 21KB and dist/cloudfour-patterns.min.js 37KB → 7.8KB, with the same seven exports. dist/cloudfour-patterns.mjs is byte-for-byte identical, which explains the asymmetry: terser's module: true pass was already doing this elimination on the ESM output, so only the UMD builds — which terser cannot treat as a module — were carrying the dead tokens. There's a patch changeset for the size win.

Decisions a reviewer might question

• TypeScript 5.9, not the current 7. rollup-plugin-dts 6 accepts ^4.5 || ^5 || ^6 || ^7, so it isn't the constraint. @typescript-eslint is: it's held at 5.17 by @cloudfour/eslint-plugin, which peers on ESLint 8. TypeScript 6 also removesmoduleResolution: "node", which tsconfig.json still uses, and 7 is the native compiler rewrite. Both belong with the lint upgrade rather than here. TypeScript 5.9 does not warn about that option, so tsconfig.json is untouched.
• The @types/node override is not removed here.Dependency modernization: Node 24, Vite, and Storybook 10 #2391 lists that as part of this PR, but the overrides block only exists on Upgrade to Storybook 10 + Vite, and Twing 7 #2405's branch — main has no override, because webpack 4's dependency tree still pins @types/node to 12.20.6 there. It becomes a rebase step for whichever of the two PRs merges second. It will work in either order: TypeScript 5 parses @types/node 26 fine, and skipLibCheck covers the residual Buffer/Uint8Array mismatches, since those are check errors rather than the parse errors TypeScript 4.9 hit.
• Type declarations shift from declare const to declare let for namespace members inferred from JS object literals. That's a TypeScript 5 declaration-emit change, and a widening, so no consumer breaks. It's the only change in dist/cloudfour-patterns.d.ts.

This PR touches neither Storybook nor Twig, so it's independent of #2405. Both edit package.json and the lockfile, so the second to merge will need a rebase.

One thing noticed but deliberately left alone: dist/cloudfour-patterns.d.ts exports defaultArgs and defaultArgTypes, which come from src/components/*/*-args.js — Storybook demo args leaking into the library's public types via the rollup entry glob. It's pre-existing on main and the same class of bug #2405 fixed for .stories.js. Worth a follow-up on #2391 rather than widening this.

Screenshots

Testing

CI covers lint, types, build, the test suite and build-storybook. What it can't judge is whether the published artifacts are actually correct, so that's what's worth checking by hand.

Run npm run build first, then:

• Confirm dist/cloudfour-patterns.js is roughly 21KB and dist/cloudfour-patterns.min.js roughly 7.8KB — both were several times larger before this change
• Confirm both files still export all seven names: grep -c 'exports\.' dist/cloudfour-patterns.js should report 7
• Confirm the three design-token values Sky Nav needs survived tree-shaking — grep -o '40em\|0\.4s\|cubic-bezier(0\.455' dist/cloudfour-patterns.js should print all three
• Confirm the token dump is gone: grep -c 'isSource' dist/cloudfour-patterns.js should report 0 (it was 172 before)
• Confirm dist/cloudfour-patterns.d.ts still declares the same exports, now using declare let instead of declare const inside the defaultArgs namespace
• Confirm dist/standalone.css is unchanged at roughly 470KB — the Sass build is not affected by this PR

Then check Sky Nav still works from the built bundle, since it's the component whose tokens were tree-shaken:

• Start Storybook and open Components → Sky Nav
• Narrow the window until the menu button appears, and confirm it opens and closes the navigation
• Confirm the open/close animation still runs smoothly rather than snapping instantly — the timing comes from one of the tree-shaken token values
• Widen the window again and confirm the navigation returns to its full horizontal layout with no menu button

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• Refs Dependency modernization: Node 24, Vite, and Storybook 10 #2391

[changeset-bot]

🦋 Changeset detected

Latest commit: eea840e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudfour/patterns	Patch

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