fix(backend): preserve run message pagination boundary

backend/app/gateway/routers/runs.py

@@ -16,7 +16,7 @@
 
 from app.gateway.authz import require_permission
 from app.gateway.deps import get_checkpointer, get_feedback_repo, get_run_event_store, get_run_manager, get_run_store, get_stream_bridge
-from app.gateway.routers.thread_runs import RunCreateRequest
+from app.gateway.routers.thread_runs import RunCreateRequest, trim_run_message_page
 from app.gateway.services import sse_consumer, start_run
 from deerflow.runtime import serialize_channel_values
 
@@ -129,8 +129,7 @@ async def run_messages(
         before_seq=before_seq,
         after_seq=after_seq,
     )
-    has_more = len(rows) > limit
-    data = rows[:limit] if has_more else rows
+    data, has_more = trim_run_message_page(rows, limit=limit, after_seq=after_seq)
     return {"data": data, "has_more": has_more}
 
 

backend/app/gateway/routers/thread_runs.py

@@ -33,6 +33,18 @@
 # ---------------------------------------------------------------------------
 
 
+def trim_run_message_page(rows: list[dict], *, limit: int, after_seq: int | None) -> tuple[list[dict], bool]:
+    """Trim a limit+1 run message page without dropping the visible boundary row."""
+    has_more = len(rows) > limit
+    if not has_more:
+        return rows, False
+
+    if after_seq is not None:
+        return rows[:limit], True
+
+    return rows[-limit:], True
+
+
 class RunCreateRequest(BaseModel):
     assistant_id: str | None = Field(default=None, description="Agent / assistant to use")
     input: dict[str, Any] | None = Field(default=None, description="Graph input (e.g. {messages: [...]})")
@@ -396,8 +408,7 @@ async def list_run_messages(
         before_seq=before_seq,
         after_seq=after_seq,
     )
-    has_more = len(rows) > limit
-    data = rows[:limit] if has_more else rows
+    data, has_more = trim_run_message_page(rows, limit=limit, after_seq=after_seq)
     return {"data": data, "has_more": has_more}
 
 

backend/tests/test_runs_api_endpoints.py

@@ -97,6 +97,55 @@ def test_run_messages_has_more_true_when_extra_row_returned():
     body = response.json()
     assert body["has_more"] is True
     assert len(body["data"]) == 50  # trimmed to limit
+    assert [m["seq"] for m in body["data"]] == list(range(2, 52))
+
+
+def test_run_messages_default_page_keeps_newest_messages_when_extra_row_returned():
+    """Default latest-page trimming drops the older sentinel row, not the newest message."""
+    rows = [_make_message(i) for i in range(16, 67)]
+    run_record = {"run_id": "run-2", "thread_id": "thread-2"}
+    app = _make_app(
+        run_store=_make_run_store(run_record),
+        event_store=_make_event_store(rows),
+    )
+    with TestClient(app) as client:
+        response = client.get("/api/runs/run-2/messages")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(17, 67))
+
+
+def test_run_messages_before_seq_page_keeps_newest_side_when_extra_row_returned():
+    """Backward pagination trims the older sentinel so adjacent pages do not miss the boundary message."""
+    rows = [_make_message(i) for i in range(1, 18)]
+    run_record = {"run_id": "run-2", "thread_id": "thread-2"}
+    app = _make_app(
+        run_store=_make_run_store(run_record),
+        event_store=_make_event_store(rows),
+    )
+    with TestClient(app) as client:
+        response = client.get("/api/runs/run-2/messages?before_seq=18&limit=16")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(2, 18))
+
+
+def test_run_messages_after_seq_page_keeps_oldest_side_when_extra_row_returned():
+    """Forward pagination still trims the newer sentinel row."""
+    rows = [_make_message(i) for i in range(11, 62)]
+    run_record = {"run_id": "run-2", "thread_id": "thread-2"}
+    app = _make_app(
+        run_store=_make_run_store(run_record),
+        event_store=_make_event_store(rows),
+    )
+    with TestClient(app) as client:
+        response = client.get("/api/runs/run-2/messages?after_seq=10")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(11, 61))
 
 
 def test_run_messages_passes_after_seq_to_event_store():

backend/tests/test_thread_run_messages_pagination.py

@@ -88,6 +88,43 @@ def test_has_more_true_when_extra_row_returned():
     body = response.json()
     assert body["has_more"] is True
     assert len(body["data"]) == 50  # trimmed to limit
+    assert [m["seq"] for m in body["data"]] == list(range(2, 52))
+
+
+def test_default_page_keeps_newest_messages_when_extra_row_returned():
+    """Default latest-page trimming drops the older sentinel row, not the newest message."""
+    rows = [_make_message(i) for i in range(16, 67)]
+    app = _make_app(event_store=_make_event_store(rows))
+    with TestClient(app) as client:
+        response = client.get("/api/threads/thread-2/runs/run-2/messages")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(17, 67))
+
+
+def test_before_seq_page_keeps_newest_side_when_extra_row_returned():
+    """Backward pagination trims the older sentinel so adjacent pages do not miss the boundary message."""
+    rows = [_make_message(i) for i in range(1, 18)]
+    app = _make_app(event_store=_make_event_store(rows))
+    with TestClient(app) as client:
+        response = client.get("/api/threads/thread-2/runs/run-2/messages?before_seq=18&limit=16")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(2, 18))
+
+
+def test_after_seq_page_keeps_oldest_side_when_extra_row_returned():
+    """Forward pagination still trims the newer sentinel row."""
+    rows = [_make_message(i) for i in range(11, 62)]
+    app = _make_app(event_store=_make_event_store(rows))
+    with TestClient(app) as client:
+        response = client.get("/api/threads/thread-2/runs/run-2/messages?after_seq=10")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["has_more"] is True
+    assert [m["seq"] for m in body["data"]] == list(range(11, 61))
 
 
 def test_after_seq_forwarded_to_event_store():