test(runtime): add Blockbuster runtime anchor for JsonlRunEventStore async IO (#3313)

* test(runtime): add Blockbuster runtime anchor for JsonlRunEventStore async IO

#3084 offloaded `JsonlRunEventStore`'s file IO via `asyncio.to_thread` and added
a mock-based offload assertion (`tests/test_jsonl_event_store_async_io.py`) that
covers `put()` only. That guard is not part of the Blockbuster runtime gate
(`tests/blocking_io/`) run by `backend-blocking-io-tests.yml`.

Add a runtime anchor that drives the full async surface (`put`, `put_batch`,
`list_messages`, `list_events`, `list_messages_by_run`, `count_messages`,
`delete_by_run`, `delete_by_thread`) under the strict Blockbuster gate, so any
blocking IO reintroduced on the event loop in any of these methods fails CI —
not only removal of a specific `to_thread` call. Verified each offloaded method
goes red when its offload is reverted. Test-only; no production change.

* test(runtime): exercise list_events event_types filter branch

Per review feedback: the anchor called list_events without event_types,
so the filter branch never ran after _read_run_events' filesystem IO.
Add a second list_events call with event_types=["message"] so the full
read path -- including the filter branch -- executes under the gate.

backend/tests/blocking_io/test_jsonl_run_event_store.py

@@ -0,0 +1,62 @@
+"""Regression anchor: JsonlRunEventStore async API must not block the loop.
+
+``JsonlRunEventStore`` is the ``run_events.backend == "jsonl"`` implementation.
+Its ``async def`` methods perform synchronous filesystem IO (``Path.glob``,
+``read_text``, ``open``, ``unlink``) that must be offloaded with
+``asyncio.to_thread`` (fixed in #3084). ``put`` runs on every emitted run event,
+so any blocking IO here stalls the event loop on the hot path.
+
+#3084 added a mock-based offload assertion in
+``tests/test_jsonl_event_store_async_io.py`` that covers ``put`` only. This
+anchor complements it by driving the **full** async surface (``put``,
+``put_batch``, ``list_messages``, ``list_events``, ``list_messages_by_run``,
+``count_messages``, ``delete_by_run``, ``delete_by_thread``) under the strict
+Blockbuster runtime gate, so any blocking IO reintroduced on the event loop in
+any of these methods — not just removal of a specific ``to_thread`` call —
+fails CI.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.asyncio
+
+
+async def test_jsonl_run_event_store_async_api_does_not_block_event_loop(tmp_path: Path) -> None:
+    from deerflow.runtime.events.store.jsonl import JsonlRunEventStore
+
+    store = JsonlRunEventStore(base_dir=str(tmp_path))
+
+    # Seed an existing run file so put()'s seq-load globs + reads, and the
+    # read/delete paths have files to scan. Test-side IO is invisible to the
+    # gate (this module is not in scanned_modules).
+    thread_dir = tmp_path / "threads" / "t1" / "runs"
+    thread_dir.mkdir(parents=True, exist_ok=True)
+    (thread_dir / "r0.jsonl").write_text('{"seq": 1, "category": "message", "run_id": "r0"}\n', encoding="utf-8")
+
+    # writes: put + put_batch
+    record = await store.put(thread_id="t1", run_id="r1", event_type="message", category="message", content="hi")
+    assert record["seq"] >= 2
+    batch = await store.put_batch(
+        [
+            {"thread_id": "t1", "run_id": "r2", "event_type": "message", "category": "message", "content": "a"},
+            {"thread_id": "t1", "run_id": "r2", "event_type": "trace", "category": "trace", "content": "b"},
+        ]
+    )
+    assert len(batch) == 2
+
+    # reads: list_messages / list_events / list_messages_by_run / count_messages.
+    # list_events is exercised both without and with the event_types filter so
+    # the filter branch runs after _read_run_events' filesystem IO.
+    assert isinstance(await store.list_messages("t1"), list)
+    assert isinstance(await store.list_events("t1", "r1"), list)
+    assert isinstance(await store.list_events("t1", "r1", event_types=["message"]), list)
+    assert isinstance(await store.list_messages_by_run("t1", "r2"), list)
+    assert await store.count_messages("t1") >= 1
+
+    # deletes: delete_by_run (single file) then delete_by_thread (remaining)
+    assert await store.delete_by_run("t1", "r2") >= 1
+    assert await store.delete_by_thread("t1") >= 1