test(writer): cover async engine path in WriterAgent/orchestrator

tests/test_phase5_writer_orchestrator.py

@@ -47,3 +47,25 @@ def test_generate_produces_filled_docx(tmp_path):
     loaded = Document(str(out))
     joined = "\n".join(p.text for p in loaded.paragraphs)
     assert "自动生成的内容" in joined
+
+
+class AsyncFakeEngine:
+    async def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+        return SimpleNamespace(
+            data={"title": variables["title"], "blocks": [{"type": "paragraph", "text": "异步引擎内容"}]},
+            status="ok",
+        )
+
+
+def test_generate_with_async_engine_produces_filled_docx(tmp_path):
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    orch = WriteOrchestrator()
+    contents = orch.generate(
+        _ss(str(tpl)), str(out), samples_dir="nonexistent_dir_xyz", engine=AsyncFakeEngine()
+    )
+    assert isinstance(contents, list) and len(contents) == 1
+    loaded = Document(str(out))
+    joined = "\n".join(p.text for p in loaded.paragraphs)
+    assert "异步引擎内容" in joined