feat(ai): generate covers without new titles

tests/test_ai.py

@@ -129,6 +129,32 @@ class AITests(TempDirMixin, unittest.TestCase):
             )
         return batch_id, db.list_tasks(batch_id=batch_id, path=cfg["db_path"])
 
+    def test_cover_title_context_and_cover_only_generation_needs(self):
+        task = SimpleNamespace(
+            stage="collected",
+            status="success",
+            old_title="旧标题",
+            new_title=None,
+            new_cover_path=None,
+            apply_attempts=0,
+        )
+
+        self.assertEqual("旧标题", ai.cover_title_context(task))
+        self.assertEqual(
+            {"title": False, "cover": True},
+            ai.generation_needs(task, generate_mode="cover"),
+        )
+        task.new_title = "新标题"
+        self.assertEqual("新标题", ai.cover_title_context(task))
+        task.new_title = None
+        task.old_title = ""
+        self.assertEqual("", ai.cover_title_context(task))
+        self.assertFalse(ai.is_generatable_task(task, generate_mode="cover"))
+        self.assertEqual(
+            {"title": True, "cover": True},
+            ai.generation_needs(task, generate_mode="title_cover"),
+        )
+
     def _write_old_cover_files(self, tasks):
         from PIL import Image
 
@@ -1644,6 +1670,68 @@ class AITests(TempDirMixin, unittest.TestCase):
 
         self.assert_removed(temp_dir)
 
+    def test_generate_batch_cover_only_uses_old_title_and_keeps_new_title_empty(self):
+        with self.make_temp_dir() as temp_dir:
+            cfg = self._config()
+            cfg["db_path"] = os.path.join(temp_dir, "cmshopee.db")
+            cfg["image_dir"] = os.path.join(temp_dir, "images")
+            cfg["ai"]["generate_mode"] = "cover"
+            cfg["ai"]["generate_cover"] = True
+            batch_id, tasks = self._collected_tasks(temp_dir, cfg, ["旧标题"])
+            cover_prompts = []
+            events = []
+
+            def fake_cover(cover_prompt, old_cover_path, out_path, **kwargs):
+                cover_prompts.append(cover_prompt)
+                os.makedirs(os.path.dirname(out_path), exist_ok=True)
+                with open(out_path, "wb") as fh:
+                    fh.write(b"jpeg")
+                return out_path
+
+            with mock.patch("app.ai.gen_title") as gen_title, \
+                    mock.patch("app.ai.gen_cover", side_effect=fake_cover) as gen_cover:
+                summary = ai.generate_batch(
+                    tasks,
+                    {"title": "标题提示", "cover": "封面 {新标题} / {旧标题}"},
+                    ai_cfg={
+                        "config": cfg,
+                        "db_path": cfg["db_path"],
+                        "on_event": events.append,
+                    },
+                )
+
+            self.assertTrue(summary["ok"])
+            self.assertEqual(0, summary["title_total"])
+            self.assertEqual(1, summary["cover_total"])
+            gen_title.assert_not_called()
+            gen_cover.assert_called_once()
+            self.assertEqual(["封面 旧标题 / 旧标题"], cover_prompts)
+            updated = db.get_task(tasks[0].id, path=cfg["db_path"])
+            self.assertIsNone(updated.new_title)
+            self.assertTrue(os.path.exists(updated.new_cover_path))
+            self.assertTrue(
+                any("使用旧标题作为封面参考" in str(event.get("detail") or "") for event in events)
+            )
+
+            cfg["ai"]["generate_mode"] = "title"
+            cfg["ai"]["generate_cover"] = False
+            with mock.patch("app.ai.gen_title", return_value="后补新标题") as gen_title, \
+                    mock.patch("app.ai.gen_cover") as gen_cover:
+                title_summary = ai.generate_batch(
+                    [updated],
+                    {"title": "标题提示", "cover": "封面"},
+                    ai_cfg={"config": cfg, "db_path": cfg["db_path"]},
+                )
+
+            self.assertTrue(title_summary["ok"])
+            gen_title.assert_called_once()
+            gen_cover.assert_not_called()
+            completed = db.get_task(tasks[0].id, path=cfg["db_path"])
+            self.assertEqual("后补新标题", completed.new_title)
+            self.assertEqual(updated.new_cover_path, completed.new_cover_path)
+
+        self.assert_removed(temp_dir)
+
     def test_generate_batch_fills_reset_cover_after_committed_history(self):
         with self.make_temp_dir() as temp_dir:
             cfg = self._config()