fix(dashboard): keep a "__proto__" key when cleaning chat messages

Review caught that the NUL-stripping copy assigned keys onto a plain
object, so a tool result key named "__proto__" (or one that became it
after cleaning) set the prototype instead of being stored. The copy now
defines own properties, with a regression test.

Author: lindesvard

packages/core/src/modules/assistant/src/persistence.test.ts

@@ -24,3 +24,13 @@ test('stripNullCharacters keeps a clean value as is', () => {
   const value = { text: 'clean', list: [1, 'two', { three: 3 }] };
   expect(stripNullCharacters(value)).toEqual(value);
 });
+
+test('stripNullCharacters keeps a __proto__ key as a plain entry', () => {
+  const value: unknown = JSON.parse(
+    '{"__proto__": {"polluted": true}, "__pr\\u0000oto__": 1}'
+  );
+  const cleaned = stripNullCharacters(value) as Record<string, unknown>;
+  expect(Object.getPrototypeOf(cleaned)).toBe(Object.prototype);
+  expect(Object.hasOwn(cleaned, '__proto__')).toBe(true);
+  expect(JSON.stringify(cleaned)).toBe('{"__proto__":1}');
+});

packages/core/src/modules/assistant/src/persistence.ts

@@ -12,11 +12,13 @@ export function stripNullCharacters<T>(value: T): T {
     return value.map(stripNullCharacters) as T;
   }
   if (value !== null && typeof value === 'object') {
-    const cleaned: Record<string, unknown> = {};
-    for (const [key, entry] of Object.entries(value)) {
-      cleaned[stripNullCharacters(key)] = stripNullCharacters(entry);
-    }
-    return cleaned as T;
+    // fromEntries defines own properties, so a "__proto__" key survives.
+    return Object.fromEntries(
+      Object.entries(value).map(([key, entry]) => [
+        stripNullCharacters(key),
+        stripNullCharacters(entry),
+      ])
+    ) as T;
   }
   return value;
 }