diff --git a/gateway/run.py b/gateway/run.py
index 487846ddc2..464637e246 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -23638,7 +23638,7 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
         is not a transactional boundary: a process crash after adapter
         acceptance can still cause durable at-least-once replay.
         """
-        source = self._build_process_event_source(evt)
+        source = await asyncio.to_thread(self._build_process_event_source, evt)
         if not source:
             # API-server-originated sessions bind a RAW session key (the
             # X-Hermes-Session-Id value — see _bind_api_server_session), not a
diff --git a/tests/gateway/test_background_process_notifications.py b/tests/gateway/test_background_process_notifications.py
index 3dfff7a206..76941bb710 100644
--- a/tests/gateway/test_background_process_notifications.py
+++ b/tests/gateway/test_background_process_notifications.py
@@ -9,6 +9,7 @@ Contributed by @PeterFile (PR #593), reimplemented on current main.
 
 import asyncio
 import queue
+import threading
 from types import SimpleNamespace
 from unittest.mock import AsyncMock
 
@@ -292,6 +293,46 @@ async def test_inject_watch_notification_carries_message_id_reply_anchor(monkeyp
     assert synth_event.source.thread_id == "24296"
 
 
+@pytest.mark.asyncio
+async def test_inject_watch_notification_loads_session_store_off_loop(monkeypatch, tmp_path):
+    from gateway.session import SessionSource
+
+    runner = _build_runner(monkeypatch, tmp_path, "all")
+    adapter = runner.adapters[Platform.TELEGRAM]
+    runner.session_store._entries["agent:main:telegram:dm:123:24296"] = SimpleNamespace(
+        origin=SessionSource(
+            platform=Platform.TELEGRAM,
+            chat_id="123",
+            chat_type="dm",
+            thread_id="24296",
+            user_id="1",
+            user_name="Fabio",
+        )
+    )
+    loop_thread = threading.get_ident()
+    load_threads = []
+    real_ensure_loaded = runner.session_store._ensure_loaded
+
+    def spy_ensure_loaded():
+        load_threads.append(threading.get_ident())
+        return real_ensure_loaded()
+
+    monkeypatch.setattr(runner.session_store, "_ensure_loaded", spy_ensure_loaded)
+
+    await runner._inject_watch_notification(
+        "[SYSTEM: Background process matched]",
+        {
+            "session_id": "proc_watch",
+            "session_key": "agent:main:telegram:dm:123:24296",
+            "message_id": "777",
+        },
+    )
+
+    adapter.handle_message.assert_awaited_once()
+    assert load_threads
+    assert all(thread_id != loop_thread for thread_id in load_threads)
+
+
 @pytest.mark.asyncio
 async def test_inject_watch_notification_ignores_foreground_event_source(monkeypatch, tmp_path):
     """Negative test: watch notification must NOT route to the foreground thread."""