fix: prevent deepStrictAssert crash on non-leaf object keys

Add `rest.length > 0` guard before recursing into nested objects,
consistent with the existing fix in `deepStrictPick`. Closes #19.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kakasoo

src/functions/DeepStrictAssert.ts

@@ -33,7 +33,7 @@ export const deepStrictAssert =
       if (input instanceof Array) {
         const elements = input.map((element) => {
           if (first in element) {
-            if (typeof element[first] === 'object' && element[first] !== null) {
+            if (typeof element[first] === 'object' && element[first] !== null && rest.length > 0) {
               return { [first]: traverse(element[first], rest) };
             }
 
@@ -46,7 +46,7 @@ export const deepStrictAssert =
         return elements;
       } else {
         if (first in input) {
-          if (typeof input[first] === 'object' && input[first] !== null) {
+          if (typeof input[first] === 'object' && input[first] !== null && rest.length > 0) {
             return { [first]: traverse(input[first], rest) };
           }
           return { [first]: input[first] };

test/features/DeepStrictAssert.ts

@@ -1,3 +1,4 @@
+import { ok } from 'assert';
 import typia, { tags } from 'typia';
 import { deepStrictAssert } from '../../src';
 
@@ -130,3 +131,14 @@ export function test_functions_deepStrictAssert_accesses_multiple_nested_array_p
   typia.assertEquals(resultD);
   typia.assertEquals(resultE);
 }
+
+/**
+ * Tests that deepStrictAssert can access a non-leaf object key without crashing.
+ * This verifies the fix for GitHub issue #19.
+ */
+export function test_functions_deepStrictAssert_accesses_non_leaf_object_key() {
+  const data = { user: { name: 'Alice', age: 30 } };
+  const result = deepStrictAssert(data)('user');
+  ok(result.user.name === 'Alice');
+  ok(result.user.age === 30);
+}