test(gateway): add overdue-policy guard for stale-agent-close recovery path

When the #54878 self-healing path drops a stale sessions.json entry, the
fix at gateway/session.py:1765 now checks _should_reset() before falling
through to DB recovery. This test covers the case where the stale entry's
session is overdue under an idle/daily reset policy — it must create a
fresh session, set auto-reset metadata, and NOT call reopen_session().

tests/gateway/test_session_store_runtime_stale_guard.py

@@ -220,3 +220,50 @@ class TestRuntimeStaleGuard:
 
         assert result.session_id != "sid_old"
         db.get_session.assert_not_called()
+
+    def test_stale_agent_close_overdue_policy_creates_fresh_session(
+        self, tmp_path,
+    ):
+        """Stale `agent_close` entry + overdue reset policy → fresh session.
+
+        The #54878 self-healing path popped the stale sessions.json entry and
+        recovered the same session_id from the DB without checking whether a
+        daily/idle reset was actually due.  This test guards the fix at
+        gateway/session.py:1765 — when the session is overdue under the
+        configured reset policy, we must create a fresh session (new id,
+        auto-reset metadata set, reopen_session NOT called).
+        """
+        source = _source()
+        # Idle policy: reset after 60 minutes of inactivity.
+        config = GatewayConfig(
+            default_reset_policy=SessionResetPolicy(mode="idle", idle_minutes=60),
+        )
+        db = _db_returning({"sid_stale": {"end_reason": "agent_close", "id": "sid_stale"}})
+        # Recovery would normally reopen this row — but it shouldn't, because
+        # the reset policy says this session is overdue.
+        db.find_latest_gateway_session_for_peer.return_value = {
+            "id": "sid_stale",
+            "started_at": (datetime.now() - timedelta(hours=3)).timestamp(),
+        }
+
+        with patch("gateway.session.SessionStore._ensure_loaded"):
+            store = SessionStore(sessions_dir=tmp_path, config=config)
+        store._db = db
+        store._loaded = True
+
+        key = store._generate_session_key(source)
+        # Entry last updated 2 hours ago → well past the 60-minute idle window.
+        store._entries[key] = _make_entry(key, "sid_stale")
+        store._entries[key].updated_at = datetime.now() - timedelta(hours=2)
+
+        result = store.get_or_create_session(source)
+
+        # Fresh session — NOT the stale session_id.
+        assert result.session_id != "sid_stale"
+        # Auto-reset metadata is set.
+        assert result.was_auto_reset is True
+        assert result.auto_reset_reason == "idle"
+        # reopen_session must NOT have been called (we skipped recovery).
+        db.reopen_session.assert_not_called()
+        # A brand-new session row was created.
+        db.create_session.assert_called_once()