diff --git a/autogpt_platform/backend/backend/api/features/chat/routes.py b/autogpt_platform/backend/backend/api/features/chat/routes.py
index 7446ddea22..6c876f3be5 100644
--- a/autogpt_platform/backend/backend/api/features/chat/routes.py
+++ b/autogpt_platform/backend/backend/api/features/chat/routes.py
@@ -875,8 +875,9 @@ async def stream_chat_post(
 
     # Atomically append user message to session BEFORE creating task to avoid
     # race condition where GET_SESSION sees task as "running" but message isn't
-    # saved yet.  append_and_save_message is idempotent — duplicate POSTs with
-    # the same content are silently skipped at the DB layer.
+    # saved yet.  append_and_save_message returns None when a duplicate is
+    # detected — in that case skip enqueue to avoid processing the message twice.
+    is_duplicate_message = False
     try:
         if request.message:
             message = ChatMessage(
@@ -890,7 +891,8 @@ async def stream_chat_post(
                     message_length=len(request.message),
                 )
             logger.info(f"[STREAM] Saving user message to session {session_id}")
-            await append_and_save_message(session_id, message)
+            saved = await append_and_save_message(session_id, message)
+            is_duplicate_message = saved is None
             logger.info(f"[STREAM] User message saved for session {session_id}")
 
         # Create a task in the stream registry for reconnection support
@@ -915,17 +917,22 @@ async def stream_chat_post(
             },
         )
 
-        await enqueue_copilot_turn(
-            session_id=session_id,
-            user_id=user_id,
-            message=request.message,
-            turn_id=turn_id,
-            is_user_message=request.is_user_message,
-            context=request.context,
-            file_ids=sanitized_file_ids,
-            mode=request.mode,
-            model=request.model,
-        )
+        if not is_duplicate_message:
+            await enqueue_copilot_turn(
+                session_id=session_id,
+                user_id=user_id,
+                message=request.message,
+                turn_id=turn_id,
+                is_user_message=request.is_user_message,
+                context=request.context,
+                file_ids=sanitized_file_ids,
+                mode=request.mode,
+                model=request.model,
+            )
+        else:
+            logger.info(
+                f"[STREAM] Duplicate message detected for session {session_id}, skipping enqueue"
+            )
     except Exception:
         raise
 
diff --git a/autogpt_platform/backend/backend/api/features/chat/routes_test.py b/autogpt_platform/backend/backend/api/features/chat/routes_test.py
index 7b9d89dee3..ff776bccb2 100644
--- a/autogpt_platform/backend/backend/api/features/chat/routes_test.py
+++ b/autogpt_platform/backend/backend/api/features/chat/routes_test.py
@@ -149,7 +149,7 @@ def _mock_stream_internals(mocker: pytest_mock.MockerFixture):
     )
     mock_save = mocker.patch(
         "backend.api.features.chat.routes.append_and_save_message",
-        return_value=None,
+        return_value=MagicMock(),  # non-None = message was saved (not a duplicate)
     )
     mock_registry = mocker.MagicMock()
     mock_registry.create_session = mocker.AsyncMock(return_value=None)
@@ -194,6 +194,26 @@ def test_stream_chat_accepts_20_file_ids(mocker: pytest_mock.MockerFixture):
     assert response.status_code == 200
 
 
+# ─── Duplicate message dedup ──────────────────────────────────────────
+
+
+def test_stream_chat_skips_enqueue_for_duplicate_message(
+    mocker: pytest_mock.MockerFixture,
+):
+    """When append_and_save_message returns None (duplicate detected),
+    enqueue_copilot_turn must NOT be called to avoid double-processing."""
+    mocks = _mock_stream_internals(mocker)
+    # Override save to return None — signalling a duplicate
+    mocks.save.return_value = None
+
+    response = client.post(
+        "/sessions/sess-1/stream",
+        json={"message": "hello"},
+    )
+    assert response.status_code == 200
+    mocks.enqueue.assert_not_called()
+
+
 # ─── UUID format filtering ─────────────────────────────────────────────
 
 
diff --git a/autogpt_platform/backend/backend/copilot/model.py b/autogpt_platform/backend/backend/copilot/model.py
index 2255e67dd4..fed3d8e8d4 100644
--- a/autogpt_platform/backend/backend/copilot/model.py
+++ b/autogpt_platform/backend/backend/copilot/model.py
@@ -647,9 +647,15 @@ async def _save_session_to_db(
             msg.sequence = existing_message_count + i
 
 
-async def append_and_save_message(session_id: str, message: ChatMessage) -> ChatSession:
+async def append_and_save_message(
+    session_id: str, message: ChatMessage
+) -> ChatSession | None:
     """Atomically append a message to a session and persist it.
 
+    Returns the updated session, or None if the message was detected as a
+    duplicate (idempotency guard). Callers must check for None and skip any
+    downstream work (e.g. enqueuing a new LLM turn) when a duplicate is detected.
+
     Uses _get_session_lock (Redis NX) to serialise concurrent writers across replicas.
     The idempotency check below provides a last-resort guard when the lock degrades.
     """
@@ -676,7 +682,7 @@ async def append_and_save_message(session_id: str, message: ChatMessage) -> Chat
             and session.messages[-1].role == message.role
             and session.messages[-1].content == message.content
         ):
-            return session
+            return None  # duplicate — caller should skip enqueue
 
         session.messages.append(message)
         existing_message_count = await chat_db().get_next_sequence(session_id)