feat(threads): paginate full history via summaries endpoint (#1022)

* feat(threads): add paginated summaries API and load full history

* fix(threads): address summaries review feedback

- validate summaries sort params and log gateway failures
- page frontend thread summaries without stale query keys or silent truncation
- export router modules and tighten thread list typing

Refs: 2901804166, 2901804176, 2901804179, 2901804180, 2901804183, 2901804187, 2901804191

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/tests/test_threads_router.py

@@ -0,0 +1,120 @@
+import asyncio
+import importlib.util
+import sys
+from pathlib import Path
+from types import SimpleNamespace
+
+_MODULE_PATH = Path(__file__).resolve().parents[1] / "src" / "gateway" / "routers" / "threads.py"
+_SPEC = importlib.util.spec_from_file_location("deerflow_threads_router", _MODULE_PATH)
+assert _SPEC and _SPEC.loader
+threads = importlib.util.module_from_spec(_SPEC)
+_SPEC.loader.exec_module(threads)
+
+
+def test_pick_title_prefers_values_title():
+    assert threads._pick_title({"title": "  Hello Title  "}) == "  Hello Title  "
+
+
+def test_pick_title_falls_back_to_untitled():
+    assert threads._pick_title({}) == "Untitled"
+    assert threads._pick_title({"title": ""}) == "Untitled"
+    assert threads._pick_title(None) == "Untitled"
+
+
+def test_to_thread_summary_returns_compact_payload():
+    row = {
+        "thread_id": "t-1",
+        "updated_at": "2026-03-08T00:00:00Z",
+        "values": {
+            "title": "Roadmap",
+            "messages": ["very", "large", "content"],
+        },
+        "other": "ignored",
+    }
+    summary = threads._to_thread_summary(row)
+    assert summary is not None
+    assert summary.thread_id == "t-1"
+    assert summary.updated_at == "2026-03-08T00:00:00Z"
+    assert summary.values == {"title": "Roadmap"}
+
+
+def test_to_thread_summary_rejects_missing_thread_id():
+    assert threads._to_thread_summary({"updated_at": "x"}) is None
+    assert threads._to_thread_summary({"thread_id": ""}) is None
+
+
+def test_resolve_langgraph_url_prefers_channels_config(monkeypatch):
+    fake_cfg = SimpleNamespace(model_extra={"channels": {"langgraph_url": "http://langgraph.internal:2024"}})
+    monkeypatch.setattr(threads, "get_app_config", lambda: fake_cfg)
+    assert threads._resolve_langgraph_url() == "http://langgraph.internal:2024"
+
+
+def test_resolve_langgraph_url_falls_back_default(monkeypatch):
+    fake_cfg = SimpleNamespace(model_extra={})
+    monkeypatch.setattr(threads, "get_app_config", lambda: fake_cfg)
+    assert threads._resolve_langgraph_url() == "http://localhost:2024"
+
+
+def test_list_thread_summaries_uses_row_count_for_next_offset(monkeypatch):
+    fake_cfg = SimpleNamespace(model_extra={})
+    monkeypatch.setattr(threads, "get_app_config", lambda: fake_cfg)
+
+    rows = [
+        {
+            "thread_id": "t-1",
+            "updated_at": "2026-03-08T00:00:00Z",
+            "values": {"title": "Roadmap"},
+        },
+        {
+            "thread_id": "",
+            "updated_at": "2026-03-08T00:01:00Z",
+            "values": {"title": "Broken row"},
+        },
+    ]
+
+    class FakeThreadsClient:
+        async def search(self, payload):
+            assert payload["limit"] == 2
+            assert payload["offset"] == 4
+            assert payload["sortBy"] == "updated_at"
+            assert payload["sortOrder"] == "desc"
+            return rows
+
+    class FakeClient:
+        threads = FakeThreadsClient()
+
+    fake_module = SimpleNamespace(get_client=lambda url: FakeClient())
+    monkeypatch.setitem(sys.modules, "langgraph_sdk", fake_module)
+
+    response = asyncio.run(threads.list_thread_summaries(limit=2, offset=4, sort_by="updated_at", sort_order="desc"))
+
+    assert [summary.thread_id for summary in response.threads] == ["t-1"]
+    assert response.next_offset == 6
+
+
+def test_list_thread_summaries_returns_none_when_last_page(monkeypatch):
+    fake_cfg = SimpleNamespace(model_extra={})
+    monkeypatch.setattr(threads, "get_app_config", lambda: fake_cfg)
+
+    rows = [
+        {
+            "thread_id": "t-1",
+            "updated_at": "2026-03-08T00:00:00Z",
+            "values": {"title": "Roadmap"},
+        }
+    ]
+
+    class FakeThreadsClient:
+        async def search(self, payload):
+            assert payload["limit"] == 2
+            return rows
+
+    class FakeClient:
+        threads = FakeThreadsClient()
+
+    fake_module = SimpleNamespace(get_client=lambda url: FakeClient())
+    monkeypatch.setitem(sys.modules, "langgraph_sdk", fake_module)
+
+    response = asyncio.run(threads.list_thread_summaries(limit=2, offset=0, sort_by="updated_at", sort_order="desc"))
+
+    assert response.next_offset is None