修复歌手为[]时误导入情况

@@ -153,15 +153,16 @@ def _select_qq_import_record(
     current_record: dict,
     candidate_records: list[dict],
     songs_by_mid: dict[str, dict],
-) -> dict | None:
-    """为导入选择 QQ 录音；当前录音的歌词或封面不可用时，改选同源的合格候选。"""
+) -> tuple[dict | None, str]:
+    """为导入选择 QQ 录音；当前录音的歌词或封面不可用时，改选同源的合格候选。
+    返回 (record, reason)，record 为 None 时 reason 说明失败原因。"""
     current_song = songs_by_mid.get(current_record['platform_unique_key'])
     if not current_song:
-        return None
+        return None, 'spider data missing'
     needs_lyric = not _has_usable_qq_lyric(current_song)
     needs_cover = not _is_usable_qq_cover(_qq_cover_source(hk_row, current_song)) or not current_song.get('album_id')
     if not needs_lyric and not needs_cover:
-        return current_record
+        return current_record, 'ok'
 
     for candidate in candidate_records:
         song = songs_by_mid.get(candidate['platform_unique_key'])
@@ -171,8 +172,13 @@ def _select_qq_import_record(
             continue
         if needs_cover and (not song.get('album_id') or not _is_usable_qq_cover(song.get('cover'))):
             continue
-        return candidate
-    return None
+        return candidate, 'ok'
+    missing = []
+    if needs_lyric:
+        missing.append('lyric')
+    if needs_cover:
+        missing.append('cover')
+    return None, f"no candidate with usable {' and '.join(missing)}"
 
 
 def _select_kugou_import_record(
@@ -180,16 +186,17 @@ def _select_kugou_import_record(
     current_record: dict,
     candidate_records: list[dict],
     songs_by_id: dict[int, dict],
-) -> dict | None:
-    """为导入选择酷狗录音；当前录音的歌词或封面不可用时，改选同源的合格候选。"""
+) -> tuple[dict | None, str]:
+    """为导入选择酷狗录音；当前录音的歌词或封面不可用时，改选同源的合格候选。
+    返回 (record, reason)，record 为 None 时 reason 说明失败原因。"""
     song_id = int(current_record['platform_unique_key'])
     current_song = songs_by_id.get(song_id)
     if not current_song:
-        return None
+        return None, 'spider data missing'
     needs_lyric = not _has_kugou_lyric(current_song)
     needs_cover = not _has_kugou_cover(hk_row, current_song)
     if not needs_lyric and not needs_cover:
-        return current_record
+        return current_record, 'ok'
 
     for candidate in candidate_records:
         cid = int(candidate['platform_unique_key'])
@@ -200,8 +207,13 @@ def _select_kugou_import_record(
             continue
         if needs_cover and not _has_kugou_cover(hk_row, song):
             continue
-        return candidate
-    return None
+        return candidate, 'ok'
+    missing = []
+    if needs_lyric:
+        missing.append('lyric')
+    if needs_cover:
+        missing.append('cover')
+    return None, f"no candidate with usable {' and '.join(missing)}"
 
 
 def _select_netease_import_record(
@@ -209,16 +221,17 @@ def _select_netease_import_record(
     current_record: dict,
     candidate_records: list[dict],
     songs_by_id: dict[int, dict],
-) -> dict | None:
-    """为导入选择网易录音；当前录音的歌词或封面不可用时，改选同源的合格候选。"""
+) -> tuple[dict | None, str]:
+    """为导入选择网易录音；当前录音的歌词或封面不可用时，改选同源的合格候选。
+    返回 (record, reason)，record 为 None 时 reason 说明失败原因。"""
     song_id = int(current_record['platform_unique_key'])
     current_song = songs_by_id.get(song_id)
     if not current_song:
-        return None
+        return None, 'spider data missing'
     needs_lyric = not _has_netease_lyric(current_song)
     needs_cover = not _has_netease_cover(hk_row, current_song)
     if not needs_lyric and not needs_cover:
-        return current_record
+        return current_record, 'ok'
 
     for candidate in candidate_records:
         cid = int(candidate['platform_unique_key'])
@@ -229,8 +242,13 @@ def _select_netease_import_record(
             continue
         if needs_cover and not _has_netease_cover(hk_row, song):
             continue
-        return candidate
-    return None
+        return candidate, 'ok'
+    missing = []
+    if needs_lyric:
+        missing.append('lyric')
+    if needs_cover:
+        missing.append('cover')
+    return None, f"no candidate with usable {' and '.join(missing)}"
 
 
 def _prepare_qq_payload(hk_row: dict, pr: dict, bucket, base_url, sp: dict, singer_list: list[dict]) -> dict:
@@ -626,6 +644,8 @@ def _prepare_import_payload(
         return None
     singer_key = int(song_data['id']) if platform == PLATFORM_QQ else int(platform_unique_id)
     singer_list = singers_maps.get(platform, {}).get(singer_key, [])
+    if not singer_list:
+        return None
     payload = preparer(hk_row, pr, bucket, base_url, song_data, singer_list)
     payload['yinyan_record'] = {
         'song_id': int(pending['song_id']),
@@ -1708,23 +1728,23 @@ def run(
                     )
                     continue
                 if platform == PLATFORM_QQ:
-                    selected = _select_qq_import_record(
+                    selected, reason = _select_qq_import_record(
                         hk_row, pr, qq_records_by_song.get(src_id, []), qq_songs_map,
                     )
                 elif platform == PLATFORM_KUGOU:
-                    selected = _select_kugou_import_record(
+                    selected, reason = _select_kugou_import_record(
                         hk_row, pr, kugou_records_by_song.get(src_id, []), kugou_songs_map,
                     )
                 elif platform == PLATFORM_NETEASE:
-                    selected = _select_netease_import_record(
+                    selected, reason = _select_netease_import_record(
                         hk_row, pr, netease_records_by_song.get(src_id, []), netease_songs_map,
                     )
                 else:
-                    selected = pr
+                    selected, reason = pr, 'ok'
                 if selected is None:
                     log.warning(
-                        'Skip import without usable lyric/cover candidate: platform=%s source_song_id=%s record_id=%s',
-                        platform, src_id, pending['record_id'],
+                        'Skip import (%s): platform=%s source_song_id=%s record_id=%s',
+                        reason, platform, src_id, pending['record_id'],
                     )
                     rejected_pending.append(pending)
                     continue

@@ -102,7 +102,7 @@ def test_qq_cover_source_keeps_valid_hk_cover():
 def test_select_qq_import_record_replaces_missing_album_cover_with_same_source_candidate():
     current = {'record_id': 10, 'platform_unique_key': 'bad-mid'}
     candidate = {'record_id': 20, 'platform_unique_key': 'good-mid'}
-    selected = runner._select_qq_import_record(
+    selected, reason = runner._select_qq_import_record(
         {'cover_url': runner.QQ_MISSING_ALBUM_COVER},
         current,
         [current, candidate],
@@ -112,12 +112,13 @@ def test_select_qq_import_record_replaces_missing_album_cover_with_same_source_c
         },
     )
     assert selected == candidate
+    assert reason == 'ok'
 
 
 def test_select_qq_import_record_replaces_missing_lyric_with_same_source_candidate():
     current = {'record_id': 10, 'platform_unique_key': 'without-lyric'}
     candidate = {'record_id': 20, 'platform_unique_key': 'with-lyric'}
-    selected = runner._select_qq_import_record(
+    selected, reason = runner._select_qq_import_record(
         {'cover_url': 'https://example.com/hk-cover.jpg'},
         current,
         [current, candidate],
@@ -127,16 +128,19 @@ def test_select_qq_import_record_replaces_missing_lyric_with_same_source_candida
         },
     )
     assert selected == candidate
+    assert reason == 'ok'
 
 
 def test_select_qq_import_record_returns_none_when_no_candidate_satisfies_missing_fields():
     current = {'record_id': 10, 'platform_unique_key': 'bad-mid'}
-    assert runner._select_qq_import_record(
+    result, reason = runner._select_qq_import_record(
         {'cover_url': runner.QQ_MISSING_ALBUM_COVER},
         current,
         [current],
         {'bad-mid': {'album_id': 0, 'cover': runner.QQ_MISSING_ALBUM_COVER, 'lyric': ''}},
-    ) is None
+    )
+    assert result is None
+    assert 'lyric' in reason and 'cover' in reason
 
 
 def test_run_imports_only_pending_yinyan_platform_record(monkeypatch):