diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a53a08d2..7dea55e1 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -154,6 +154,12 @@ jobs:
       - name: Install
         working-directory: infrastructure
         run: npm ci --prefer-offline
+      - name: Type-check (tsc --noEmit)
+        working-directory: infrastructure
+        # Single shared type-check for the whole project. jest now transpiles
+        # only (isolatedModules), so this is where infra type errors are caught
+        # on a PR — cheaper once here than re-run inside every jest worker.
+        run: npm run build
       - name: Run tests
         working-directory: infrastructure
         run: npx jest --maxWorkers=2
diff --git a/infrastructure/jest.config.js b/infrastructure/jest.config.js
index e9a42040..15b3c4cb 100644
--- a/infrastructure/jest.config.js
+++ b/infrastructure/jest.config.js
@@ -4,6 +4,12 @@ module.exports = {
   testMatch: ['**/*.test.ts'],
   transform: {
     '^.+\\.tsx?$': ['ts-jest', {
+      // Transpile-only: skip per-worker type-checking (each jest worker
+      // otherwise re-type-checks the whole project with no shared cache, the
+      // dominant cost of this suite). Type safety is enforced once by the
+      // `tsc --noEmit` step in the CI job (.github/workflows/tests.yml) and by
+      // `npm run build` locally. Safe here: no `const enum` in the tree.
+      isolatedModules: true,
       diagnostics: {
         ignoreCodes: [151002],
       },