Run the suite on Vitest and make the tooling strict TypeScript #22

Parent

#21

What to build

Every existing suite runs on Vitest instead of node:test, and every script and test is TypeScript that Node runs directly. After this lands, a contributor on a fresh clone runs nvm use, npm ci and npm run verify, and gets the same strict, typed and measured gate that CI runs.

• Vitest 4 with V8 coverage replaces node:test and c8. A shared setup makes any network call fail the test that made it, and gives each test its own temporary directory.
• Lint rejects a committed .only or .skip, a fixed sleep in a test, and a test that asserts nothing.
• Coverage thresholds are set from what the suite reaches after the migration, over an explicit include list so an untested file counts as zero, and are only ever raised. A count of coverage-ignore comments is held at zero.
• Scripts and tests are TypeScript, run by Node's type stripping, and included in the typecheck.
• TypeScript is pinned to an exact 6.0.x, and ESLint 10 runs strictTypeChecked with type information. The tsconfig gains erasableSyntaxOnly, noUnusedLocals, noUnusedParameters, noFallthroughCasesInSwitch and isolatedModules. Prettier stays.
• .nvmrc pins an exact Node 24.x, and CI reads it.
• The npm package ships docs/adr and spec only, because Node does not strip types inside node_modules.
• Two ADRs in docs/adr/architecture/: tests run on Vitest and tooling is TypeScript under Node's type stripping; coverage is a ratchet.

Acceptance criteria

• npm run verify passes locally on the pinned Node and in CI.
• No JavaScript source remains among the scripts and tests, and every suite runs on Vitest.
• A test that calls the network fails with a message naming the test.
• Lint fails on a committed .only, on a fixed sleep in a test, and on a test with no assertion.
• The coverage thresholds equal the measured values, and the config records the measurement beside them.
• npm pack --dry-run lists docs/adr and spec, and no TypeScript script.
• Both ADRs pass npm run lint:adrs and have rows in the register.

Blocked by

None (can start immediately).