test(chat): 覆盖系统撤回/群名片/实时会话同步相关用例

- 新增系统撤回消息 replacemsg 解析与导出语义测试

- 新增群聊会话预览格式化与群名片 ext_buffer 解析测试

- 新增 realtime 会话列表与 sync_all 落库 last_sender_display_name 测试

tests/test_group_nickname_ext_buffer_parsing.py

@@ -0,0 +1,114 @@
+import sqlite3
+import sys
+import unittest
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT / "src"))
+
+from wechat_decrypt_tool.chat_helpers import _load_group_nickname_map_from_contact_db
+
+
+def _enc_varint(n: int) -> bytes:
+    v = int(n)
+    out = bytearray()
+    while True:
+        b = v & 0x7F
+        v >>= 7
+        if v:
+            out.append(b | 0x80)
+        else:
+            out.append(b)
+            break
+    return bytes(out)
+
+
+def _enc_tag(field_no: int, wire_type: int) -> bytes:
+    return _enc_varint((int(field_no) << 3) | int(wire_type))
+
+
+def _enc_len(field_no: int, data: bytes) -> bytes:
+    b = bytes(data or b"")
+    return _enc_tag(field_no, 2) + _enc_varint(len(b)) + b
+
+
+def _member_entry(*, inner: bytes) -> bytes:
+    # contact.db ext_buffer uses repeated length-delimited submessages; the top-level field number is not important
+    # for our best-effort parser, so we use field 1.
+    return _enc_len(1, inner)
+
+
+class TestGroupNicknameExtBufferParsing(unittest.TestCase):
+    def test_parse_pattern_a_field1_username_field2_display(self):
+        chatroom = "demo@chatroom"
+        username = "wxid_demo_123456"
+        display = "群名片A"
+
+        inner = _enc_len(1, username.encode("utf-8")) + _enc_len(2, display.encode("utf-8"))
+        ext_buffer = _member_entry(inner=inner)
+
+        with TemporaryDirectory() as td:
+            contact_db_path = Path(td) / "contact.db"
+            conn = sqlite3.connect(str(contact_db_path))
+            try:
+                conn.execute(
+                    "CREATE TABLE chat_room(id INTEGER PRIMARY KEY, username TEXT, owner TEXT, ext_buffer BLOB)"
+                )
+                conn.execute(
+                    "INSERT INTO chat_room(id, username, owner, ext_buffer) VALUES (?, ?, ?, ?)",
+                    (1, chatroom, "", ext_buffer),
+                )
+                conn.commit()
+            finally:
+                conn.close()
+
+            out = _load_group_nickname_map_from_contact_db(contact_db_path, chatroom, [username])
+            self.assertEqual(out.get(username), display)
+
+    def test_parse_pattern_b_field4_username_field1_display(self):
+        chatroom = "demo2@chatroom"
+        username = "wxid_demo_abcdef"
+        display = "hjlbingo"
+
+        inner = _enc_len(4, username.encode("utf-8")) + _enc_len(1, display.encode("utf-8"))
+        ext_buffer = _member_entry(inner=inner)
+
+        with TemporaryDirectory() as td:
+            contact_db_path = Path(td) / "contact.db"
+            conn = sqlite3.connect(str(contact_db_path))
+            try:
+                conn.execute(
+                    "CREATE TABLE chat_room(id INTEGER PRIMARY KEY, username TEXT, owner TEXT, ext_buffer BLOB)"
+                )
+                conn.execute(
+                    "INSERT INTO chat_room(id, username, owner, ext_buffer) VALUES (?, ?, ?, ?)",
+                    (1, chatroom, "", ext_buffer),
+                )
+                conn.commit()
+            finally:
+                conn.close()
+
+            out = _load_group_nickname_map_from_contact_db(contact_db_path, chatroom, [username])
+            self.assertEqual(out.get(username), display)
+
+    def test_non_chatroom_returns_empty(self):
+        with TemporaryDirectory() as td:
+            contact_db_path = Path(td) / "contact.db"
+            conn = sqlite3.connect(str(contact_db_path))
+            try:
+                conn.execute(
+                    "CREATE TABLE chat_room(id INTEGER PRIMARY KEY, username TEXT, owner TEXT, ext_buffer BLOB)"
+                )
+                conn.commit()
+            finally:
+                conn.close()
+
+            out = _load_group_nickname_map_from_contact_db(contact_db_path, "wxid_not_chatroom", ["wxid_xxx"])
+            self.assertEqual(out, {})
+
+
+if __name__ == "__main__":
+    unittest.main()
+