feat(events): add pagination to list_messages_by_run on all store backends

Replicates the existing before_seq/after_seq/limit cursor-pagination pattern
from list_messages onto list_messages_by_run across the abstract interface,
MemoryRunEventStore, JsonlRunEventStore, and DbRunEventStore.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/test_run_event_store_pagination.py

@@ -0,0 +1,107 @@
+"""Tests for paginated list_messages_by_run across all RunEventStore backends."""
+import pytest
+
+from deerflow.runtime.events.store.memory import MemoryRunEventStore
+
+
+@pytest.fixture
+def base_store():
+    return MemoryRunEventStore()
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_default_returns_all(base_store):
+    store = base_store
+    for i in range(7):
+        await store.put(
+            thread_id="t1", run_id="run-a",
+            event_type="human_message" if i % 2 == 0 else "ai_message",
+            category="message", content=f"msg-a-{i}",
+        )
+    for i in range(3):
+        await store.put(
+            thread_id="t1", run_id="run-b",
+            event_type="human_message", category="message", content=f"msg-b-{i}",
+        )
+    await store.put(thread_id="t1", run_id="run-a", event_type="tool_call", category="trace", content="trace")
+
+    msgs = await store.list_messages_by_run("t1", "run-a")
+    assert len(msgs) == 7
+    assert all(m["category"] == "message" for m in msgs)
+    assert all(m["run_id"] == "run-a" for m in msgs)
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_with_limit(base_store):
+    store = base_store
+    for i in range(7):
+        await store.put(
+            thread_id="t1", run_id="run-a",
+            event_type="human_message" if i % 2 == 0 else "ai_message",
+            category="message", content=f"msg-a-{i}",
+        )
+
+    msgs = await store.list_messages_by_run("t1", "run-a", limit=3)
+    assert len(msgs) == 3
+    seqs = [m["seq"] for m in msgs]
+    assert seqs == sorted(seqs)
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_after_seq(base_store):
+    store = base_store
+    for i in range(7):
+        await store.put(
+            thread_id="t1", run_id="run-a",
+            event_type="human_message" if i % 2 == 0 else "ai_message",
+            category="message", content=f"msg-a-{i}",
+        )
+
+    all_msgs = await store.list_messages_by_run("t1", "run-a")
+    cursor_seq = all_msgs[2]["seq"]
+    msgs = await store.list_messages_by_run("t1", "run-a", after_seq=cursor_seq, limit=50)
+    assert all(m["seq"] > cursor_seq for m in msgs)
+    assert len(msgs) == 4
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_before_seq(base_store):
+    store = base_store
+    for i in range(7):
+        await store.put(
+            thread_id="t1", run_id="run-a",
+            event_type="human_message" if i % 2 == 0 else "ai_message",
+            category="message", content=f"msg-a-{i}",
+        )
+
+    all_msgs = await store.list_messages_by_run("t1", "run-a")
+    cursor_seq = all_msgs[4]["seq"]
+    msgs = await store.list_messages_by_run("t1", "run-a", before_seq=cursor_seq, limit=50)
+    assert all(m["seq"] < cursor_seq for m in msgs)
+    assert len(msgs) == 4
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_does_not_include_other_run(base_store):
+    store = base_store
+    for i in range(7):
+        await store.put(
+            thread_id="t1", run_id="run-a",
+            event_type="human_message", category="message", content=f"msg-a-{i}",
+        )
+    for i in range(3):
+        await store.put(
+            thread_id="t1", run_id="run-b",
+            event_type="human_message", category="message", content=f"msg-b-{i}",
+        )
+
+    msgs = await store.list_messages_by_run("t1", "run-b")
+    assert len(msgs) == 3
+    assert all(m["run_id"] == "run-b" for m in msgs)
+
+
+@pytest.mark.anyio
+async def test_list_messages_by_run_empty_run(base_store):
+    store = base_store
+    msgs = await store.list_messages_by_run("t1", "nonexistent")
+    assert msgs == []