build: replace rollup/babel/terser build with tsdown

Collapse the hand-rolled Rollup orchestrator (scripts/configs.cjs +
config-types.cjs + build.main.cjs, 373 lines) and 8 build devDeps into one
tsdown.config.ts (rolldown engine + built-in dts). Chosen over tsup after a
problem-blind Codex assessment and a spike: tsdown emits constructor-direct
CJS (require('fuse.js') === Fuse) and named worker CJS automatically, no
footer hacks.

Behavior-preserving on the public surface:
- identical 15-file dist set (12 runtime + 3 dts)
- CJS require() contract unchanged; named fuse-worker.cjs export preserved
- feature-flag DCE intact (basic build strips logical/extended/token)
- dev/prod default-export split preserved
- Fuse.version injected via define (bare __VERSION__ + ambient declare;
  honors process.env.VERSION for releases)

Worker-URL resolution no longer depends on a bundler's import.meta.url
codegen: a per-format __WORKER_IS_CJS__ define routes browser-CJS to a
document base while ESM keeps the literal new URL('./fuse.worker.mjs',
import.meta.url) so bundlers still detect and rewrite the worker asset.
test/worker-url.test.js gates node-ESM, node-CJS, browser-ESM (Vite), and
browser-CJS. test/cjs-interop.test.js gates require() === constructor for
every lib cjs plus the named worker cjs.

Sizes: minified artifacts are 287-313 bytes smaller raw; gzip is +8..+28
bytes (<=0.4%, accepted) since rolldown's minifier compresses marginally
worse than Terser.

Build/release now requires Node >=22.18 (tsdown engines): CI builds on 22/24
and runs the Node 20 leg against the committed dist. docs-deploy
reconciliation is descoped (deploy-docs.sh is the only path that bumps docs
before deploy; needs a release-ordering fix first).

Removed devDeps: rollup, @rollup/plugin-babel, @rollup/plugin-node-resolve,
@rollup/plugin-replace, @babel/core, @babel/preset-typescript, terser,
rollup-plugin-dts. Added: tsdown.

Author: krisk

.github/workflows/nodejs.yml

@@ -26,5 +26,9 @@ jobs:
         with:
           node-version: ${{ matrix.node }}
       - run: npm install --prefer-offline --no-audit --no-fund
+      # The build tool (tsdown) requires Node >= 22.18. The published library and
+      # its tests still run on Node 20: that leg tests the committed dist rather
+      # than rebuilding. Node 22/24 rebuild from source before testing.
       - run: npm run build
+        if: matrix.node != '20'
       - run: npm run test

.nvmrc

@@ -1 +1 @@
-20
+22

DEVELOPERS.md

@@ -7,6 +7,8 @@
 
 ## <a name="setup"></a> Setup
 
+Building and releasing require **Node >= 22.18** (the bundler, [tsdown](https://tsdown.dev), needs it); `nvm use` picks up the pinned `.nvmrc`. The published library runs on far older Node, and the CI test matrix still includes Node 20.
+
 ```shell
 npm install
 ```
@@ -19,8 +21,7 @@ npm install
 | `npm test` | Run the test suite (vitest) |
 | `npm run typecheck` | Type-check the source without emitting |
 | `npm run lint` | Lint source and tests (eslint) |
-| `npm run dev` | Watch mode for ESM dev build |
-| `npm run dev:cjs` | Watch mode for CJS dev build |
+| `npm run dev` | Watch mode (rebuilds all dist targets via tsdown) |
 | `npm run bench` | Build, then run the core search + index regression benchmarks |
 | `npm run bench:search` | Search benchmark (object/string fuzzy, scaling, remove) |
 | `npm run bench:index` | Index creation benchmark across dataset sizes |
@@ -30,7 +31,7 @@ npm install
 
 ## <a name="structure"></a> Project Structure
 
-Source is TypeScript. Types are emitted from source via `rollup-plugin-dts`.
+Source is TypeScript. The build, including `.d.ts` emit, runs through [tsdown](https://tsdown.dev) (rolldown engine); see `tsdown.config.ts`.
 
 ```
 src/
@@ -42,7 +43,8 @@ src/
   entry.ts      — Entry point with static methods and type exports
 test/           — Tests and fixtures
 bench/          — Benchmarks (search, index creation, extended, tokens, workers)
-scripts/        — Rollup build configs
+tsdown.config.ts — Build config (all dist targets + types)
+scripts/        — Release + docs helpers (bump-docs, deploy-docs, release)
 dist/           — Built output (CJS, ESM, .d.ts)
 ```