feat(dingtalk): add disable_private_chat to reject 1:1 DMs

Add a `disable_private_chat` config flag (JSON alias `disablePrivateChat`,
default False) to the DingTalk channel. When enabled, any non-group (1:1)
message is rejected with a Chinese notice directing the user to group chat
("该机器人未开启私聊，请在群聊中与我对话。") before permission/pairing logic
runs, so even allowlisted senders are redirected. Group messages are
unaffected.

Co-Authored-By: Claude <noreply@anthropic.com>

nanobot/channels/dingtalk/runtime.py

@@ -175,6 +175,7 @@ class DingTalkConfig(Base):
     allow_remote_media_redirects: bool = False
     remote_media_redirect_allowed_hosts: list[str] = Field(default_factory=list)
     group_user_isolation: bool = False  # If True, each user in group chat gets their own session
+    disable_private_chat: bool = False  # If True, reject 1:1 DMs with a notice; group chats only
 
 
 class DingTalkChannel(BaseChannel):
@@ -750,6 +751,21 @@ class DingTalkChannel(BaseChannel):
             session_key = None
             if is_group and self.config.group_user_isolation:
                 session_key = f"{self.name}:group:{conversation_id}:{sender_id}"
+
+            if not is_group and self.config.disable_private_chat:
+                # Private chat is disabled: reply with a notice and drop the
+                # message before any permission/pairing logic runs, so even
+                # allowlisted users are redirected to group chat.
+                self.logger.info("private chat disabled; rejecting DM from {}", sender_name)
+                await self.send(
+                    OutboundMessage(
+                        channel=self.name,
+                        chat_id=str(chat_id),
+                        content="该机器人未开启私聊，请在群聊中与我对话。",
+                    )
+                )
+                return
+
             await self._handle_message(
                 sender_id=sender_id,
                 chat_id=chat_id,

nanobot/channels/dingtalk/tests/test_dingtalk_channel.py

@@ -153,6 +153,85 @@ async def test_group_user_isolation_true_separates_sessions() -> None:
     assert msg1.chat_id == msg2.chat_id == "group:conv123"
 
 
+@pytest.mark.asyncio
+async def test_dm_rejected_when_private_chat_disabled(monkeypatch) -> None:
+    """With disable_private_chat=True, a 1:1 DM is rejected: nothing reaches the
+    bus (no session is created) and the bot replies with a notice directing the
+    user to group chat. Even allowlisted senders are blocked in DMs."""
+    config = DingTalkConfig(
+        client_id="app",
+        client_secret="secret",
+        allow_from=["*"],  # even allowlisted senders are blocked in DMs
+        disable_private_chat=True,
+    )
+    bus = MessageBus()
+    channel = DingTalkChannel(config, bus)
+
+    async def fake_get_token():
+        return "test-token"
+
+    monkeypatch.setattr(channel, "_get_access_token", fake_get_token)
+    channel._http = _FakeHttp()
+
+    await channel._on_message(
+        "hello",
+        sender_id="user1",
+        sender_name="Alice",
+        conversation_type="1",
+    )
+
+    # No inbound message was published -> no session created
+    assert bus.inbound.empty()
+
+    # A notice was sent back to the DM user via the private-chat API
+    assert len(channel._http.calls) == 1
+    call = channel._http.calls[0]
+    assert call["url"] == "https://api.dingtalk.com/v1.0/robot/oToMessages/batchSend"
+    assert call["json"]["msgKey"] == "sampleMarkdown"
+    assert call["json"]["userIds"] == ["user1"]
+    assert "该机器人未开启私聊，请在群聊中与我对话。" in call["json"]["msgParam"]
+
+
+@pytest.mark.asyncio
+async def test_dm_allowed_when_private_chat_not_disabled() -> None:
+    """By default (disable_private_chat=False), a 1:1 DM still reaches the bus."""
+    config = DingTalkConfig(client_id="app", client_secret="secret", allow_from=["*"])
+    bus = MessageBus()
+    channel = DingTalkChannel(config, bus)
+
+    await channel._on_message(
+        "hello",
+        sender_id="user1",
+        sender_name="Alice",
+        conversation_type="1",
+    )
+
+    msg = await bus.consume_inbound()
+    assert msg.chat_id == "user1"
+    assert msg.metadata["conversation_type"] == "1"
+
+
+@pytest.mark.asyncio
+async def test_group_message_allowed_when_private_chat_disabled() -> None:
+    """Disabling private chat must not affect group messages."""
+    config = DingTalkConfig(
+        client_id="app", client_secret="secret", allow_from=["*"], disable_private_chat=True
+    )
+    bus = MessageBus()
+    channel = DingTalkChannel(config, bus)
+
+    await channel._on_message(
+        "hello",
+        sender_id="user1",
+        sender_name="Alice",
+        conversation_type="2",
+        conversation_id="conv123",
+    )
+
+    msg = await bus.consume_inbound()
+    assert msg.chat_id == "group:conv123"
+
+
 @pytest.mark.asyncio
 async def test_group_send_uses_group_messages_api() -> None:
     config = DingTalkConfig(client_id="app", client_secret="secret", allow_from=["*"])