Type declaration checks

From the repository root, use a modern Node.js version (Node 24 in CI):

npm ci --prefix test/types
npm run test:types

The isolated, locked toolchain compiles the same fixture with TypeScript 5.9.3 against both @types/koa 2.11.0 and 2.15.2. The legacy alias and TypeScript path mapping let both versions run without reinstalling or changing the lockfile.

The fixture covers existing imports, option types, bypass callbacks, custom state/context propagation, and rejection of invalid field access. Both checks use strict checking without skipLibCheck. Do not execute the fixture as JavaScript.

This tooling is separate from the runtime Mocha suite: its Node.js requirements do not set a minimum runtime version for users of the library. The runtime suite runs against Node 12, 14, 16, 18, 20, 22 and 24 in CI.