diff --git a/package.json b/package.json
index f868824..b4a9073 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,7 @@
   "scripts": {
     "build": "tsc",
     "test": "vitest run",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit && tsc -p tsconfig.test.json"
   },
   "devDependencies": {
     "@types/node": "^22.0.0",
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..2b538dd
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,13 @@
+{
+  // Type-check the test files too. The base tsconfig.json excludes
+  // **/*.test.ts so `build` (tsc emit) never writes test declarations into
+  // dist/; this config re-includes them under --noEmit so `typecheck` actually
+  // verifies the contract test — the repo's whole deliverable.
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "noEmit": true,
+    "declaration": false
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}