diff --git a/INSTRUCTIONS.md b/INSTRUCTIONS.md
index aca03b9a..7180b98a 100644
--- a/INSTRUCTIONS.md
+++ b/INSTRUCTIONS.md
@@ -32,6 +32,7 @@
 
   - Prefer `interface` for object structures; `type` for unions/intersections.
   - Avoid `any` at all costs (in both source and tests); use `unknown`, proper generics, or `as unknown as T` for unavoidable type coercions. In tests, use `assert` (imported from `vitest`) for type narrowing.
+  - Never use non-null assertions (`!`); use a null check with an early return or conditional instead.
   - Use `zod` for runtime validation if external data is involved.
   - `noUnusedParameters` and `noImplicitReturns` are enforced — all parameters must be used and all code paths must return.
 
diff --git a/eslint.config.mjs b/eslint.config.mjs
index aea9088e..a0b1811c 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -23,6 +23,8 @@ export default defineConfig([
       sourceType: 'module',
     },
 
-    rules: {},
+    rules: {
+      curly: 'error',
+    },
   },
 ]);