fix(content): guard optional durationMs and cover loop validation

src/content/__tests__/schema.test.ts

@@ -208,4 +208,21 @@ describe('action kind schema', () => {
     });
     expect(content.actionsById.rest.kind).toBe('loop');
   });
+
+  it('rejects loop action without durationMs', () => {
+    expect(() =>
+      buildContent({
+        resources: [{ id: 'supplies', name: 'Supplies' }],
+        actions: [
+          {
+            id: 'broken_loop',
+            name: 'Broken loop',
+            kind: 'loop',
+            group: { id: 'camp', label: 'Camp' },
+            yields: [],
+          },
+        ],
+      }),
+    ).toThrow(/durationMs/);
+  });
 });