chore: pin the Node version in .nvmrc and read it from CI (closes #93)

.github/workflows/ci.yml

@@ -10,16 +10,14 @@ jobs:
   test-unit:
     name: Lint & Unit Tests (TypeScript)
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        node-version: [20.x]
     steps:
       - uses: actions/checkout@v4
 
-      - name: Use Node.js ${{ matrix.node-version }}
+      # Version comes from .nvmrc so `nvm use` locally and CI cannot drift.
+      - name: Use Node.js from .nvmrc
         uses: actions/setup-node@v4
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version-file: '.nvmrc'
           cache: 'npm'
 
       - name: Install dependencies
@@ -64,16 +62,13 @@ jobs:
     name: End-to-End Integration Tests
     runs-on: ubuntu-latest
     needs: test-unit
-    strategy:
-      matrix:
-        node-version: [20.x]
     steps:
       - uses: actions/checkout@v4
 
-      - name: Use Node.js ${{ matrix.node-version }}
+      - name: Use Node.js from .nvmrc
         uses: actions/setup-node@v4
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version-file: '.nvmrc'
           cache: 'npm'
 
       - name: Install dependencies

.nvmrc

@@ -0,0 +1 @@
+20

CONTRIBUTING.md

@@ -96,7 +96,9 @@ new package rather than being bolted onto an existing one — open an issue to d
 
 ## Code style
 
-- TypeScript, Node 20+. Formatting is enforced by Prettier/ESLint (`npm run lint`).
+- TypeScript, Node 20+. The exact version CI uses is pinned in `.nvmrc` — run
+  `nvm use` in the repo root to match it. Formatting is enforced by
+  Prettier/ESLint (`npm run lint`).
 - Prefer small, focused functions and explicit types on exported APIs.
 - Don't vendor `compliance-primitives` contract code here — reference it as a dependency/link.