diff --git a/CHANGELOG.md b/CHANGELOG.md
index 54ba21c039..ec81fa0fa7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -697,6 +697,13 @@ This release closes that milestone with **439 merged pull requests**.
 
 ### Fixed
 
+- **channels:** Opening an IM-channel conversation on the web while its run is still
+  going no longer shows the user's message twice. Channel run input carried no
+  message id, so the Gateway stored it id-less in the run record while the
+  checkpoint copy received a generated uuid, and the web client's reconnect
+  hydration, which matches the two copies by id, kept both until the run
+  finished. Channel human messages now carry their own id, so both copies share
+  it. ([#6401])
 - **deploy:** `make up`, `make down` and `make prod-logs` no longer stop on a
   fresh checkout with `env file .../.env not found`. `.env` and `frontend/.env` are gitignored and
   `make up` does not create them, but the production compose file required
@@ -8952,3 +8959,4 @@ with **180 merged pull requests** since the first 2.0 milestone tag.
 [#6370]: https://github.com/bytedance/deer-flow/pull/6370
 [#6378]: https://github.com/bytedance/deer-flow/pull/6378
 [#6388]: https://github.com/bytedance/deer-flow/pull/6388
+[#6401]: https://github.com/bytedance/deer-flow/pull/6401
diff --git a/CHANGELOG_zh.md b/CHANGELOG_zh.md
index 5c6890b30d..989b8867d2 100644
--- a/CHANGELOG_zh.md
+++ b/CHANGELOG_zh.md
@@ -615,6 +615,9 @@
 
 ### 修复
 
+- **渠道：** 在 IM 渠道会话的运行尚未结束时从网页打开它，用户消息不再显示两次。渠道运行输入此前不带消息 id，
+  Gateway 在运行记录中按原样保存无 id 的消息，而检查点中的副本会被分配新的 uuid；网页客户端重连时按 id
+  合并这两份副本，因此在运行结束前两条都会显示。现在渠道发送的人类消息自带 id，两份副本共享同一 id。([#6401])
 - **部署：** 在全新检出的仓库上，`make up`、`make down` 与 `make prod-logs` 
   不再因 `env file .../.env not found` 而中止。`.env` 与
   `frontend/.env` 已被 gitignore，`make up` 也不会创建它们，但生产 compose 文件此前要求两者都存在。
@@ -7389,3 +7392,4 @@ DeerFlow 2.0 是围绕"超级智能体"框架的彻底重写，核心包含子
 [#6370]: https://github.com/bytedance/deer-flow/pull/6370
 [#6378]: https://github.com/bytedance/deer-flow/pull/6378
 [#6388]: https://github.com/bytedance/deer-flow/pull/6388
+[#6401]: https://github.com/bytedance/deer-flow/pull/6401
diff --git a/backend/app/channels/manager.py b/backend/app/channels/manager.py
index dbfe34faf3..b305dcc34e 100644
--- a/backend/app/channels/manager.py
+++ b/backend/app/channels/manager.py
@@ -9,6 +9,7 @@ import mimetypes
 import re
 import stat
 import time
+import uuid
 from collections import OrderedDict
 from collections.abc import Awaitable, Callable, Mapping
 from dataclasses import dataclass
@@ -911,7 +912,10 @@ def _unknown_command_reply(command: str | None = None) -> str:
 
 
 def _human_input_message(content: str, *, original_content: str | None = None, files: list[dict[str, Any]] | None = None) -> dict[str, Any]:
-    message: dict[str, Any] = {"role": "human", "content": content}
+    # The Gateway records run input as sent, but add_messages gives an id-less
+    # message a fresh uuid in the checkpoint. A web client reconnecting to the
+    # run rebuilds its input from both copies and can only match them by id.
+    message: dict[str, Any] = {"id": str(uuid.uuid4()), "role": "human", "content": content}
     if original_content is not None and original_content != content or files:
         additional_kwargs: dict[str, Any] = {}
         if original_content is not None and original_content != content:
diff --git a/backend/tests/test_channels.py b/backend/tests/test_channels.py
index 698a291493..f02e028fae 100644
--- a/backend/tests/test_channels.py
+++ b/backend/tests/test_channels.py
@@ -1197,6 +1197,59 @@ class TestChannelManager:
 
         _run(go())
 
+    def test_run_input_message_has_a_unique_id(self):
+        """Each run's human message carries its own id.
+
+        The Gateway stores run input as sent, while ``add_messages`` gives an
+        id-less message a fresh uuid in the checkpoint. A web client that
+        reconnects to a running channel thread rebuilds the input from both
+        copies and can only match them by id.
+        """
+        from app.channels.manager import ChannelManager
+
+        async def go():
+            bus = MessageBus()
+            store = ChannelStore(path=Path(tempfile.mkdtemp()) / "store.json")
+            manager = ChannelManager(bus=bus, store=store)
+
+            outbound_received = []
+
+            async def capture_outbound(msg):
+                outbound_received.append(msg)
+
+            bus.subscribe_outbound(capture_outbound)
+
+            mock_client = _make_mock_langgraph_client()
+            manager._client = mock_client
+
+            await manager.start()
+            for text in ("first", "second"):
+                await bus.publish_inbound(InboundMessage(channel_name="test", chat_id="chat1", user_id="user1", text=text))
+            await _wait_for(lambda: len(outbound_received) >= 2)
+            await manager.stop()
+
+            ids = [call.kwargs["input"]["messages"][0].get("id") for call in mock_client.runs.wait.call_args_list]
+            assert len(ids) == 2
+            assert all(isinstance(message_id, str) and message_id for message_id in ids)
+            assert ids[0] != ids[1]
+
+        _run(go())
+
+    def test_run_input_message_id_matches_its_checkpoint_copy(self):
+        """The id a channel sends survives run admission into both copies."""
+        from langgraph.graph.message import add_messages
+
+        from app.channels.manager import _human_input_message
+        from app.gateway.services import _canonical_run_record_input, normalize_input
+
+        raw_input = {"messages": [_human_input_message("hello", original_content="/skill hello")]}
+        graph_input = normalize_input(raw_input, trusted_internal=True)
+
+        record = _canonical_run_record_input(raw_input, graph_input)
+        checkpoint_messages = add_messages([], graph_input["messages"])
+
+        assert record["messages"][0]["id"] == checkpoint_messages[0].id == raw_input["messages"][0]["id"]
+
     def test_worker_pool_dedupes_stable_provider_message_id(self, tmp_path):
         from app.channels.manager import ChannelManager
 
@@ -4810,7 +4863,9 @@ class TestGithubFollowupBuffer:
             await manager._drain_followups_for_thread(mock_client, thread_id, carrier_msg)
 
             mock_client.runs.create.assert_called_once()
-            drained_text = mock_client.runs.create.call_args[1]["input"]["messages"][0]["content"]
+            drained_message = mock_client.runs.create.call_args[1]["input"]["messages"][0]
+            drained_text = drained_message["content"]
+            assert isinstance(drained_message.get("id"), str) and drained_message["id"]
             for i in range(FOLLOWUP_DRAIN_BATCH_SIZE):
                 assert f"comment {i}" in drained_text
             for i in range(FOLLOWUP_DRAIN_BATCH_SIZE, 15):