fix(agent99): bound DB sessions and expire stale outcomes

apps/api/tests/test_runtime_bootstrap_guards.py

@@ -8,6 +8,7 @@ Runtime bootstrap guard tests.
 
 from __future__ import annotations
 
+import asyncio
 import inspect
 from collections.abc import Awaitable
 from pathlib import Path
@@ -223,6 +224,52 @@ def test_get_engine_uses_null_pool_for_bounded_background_processes(monkeypatch)
     assert "pool_timeout" not in captured
 
 
+@pytest.mark.asyncio
+async def test_null_pool_session_limiter_serializes_worker_db_sessions(
+    monkeypatch,
+) -> None:
+    from src.db import base as db_base
+
+    assert "async with _database_session_slot()" in inspect.getsource(
+        db_base.get_db
+    )
+    assert "async with _database_session_slot()" in inspect.getsource(
+        db_base.get_db_context
+    )
+    monkeypatch.setattr(db_base.settings, "DATABASE_NULL_POOL", True)
+    monkeypatch.setattr(
+        db_base.settings,
+        "DATABASE_NULL_POOL_CONCURRENCY_LIMIT",
+        1,
+    )
+    monkeypatch.setattr(db_base.settings, "DATABASE_POOL_TIMEOUT_SECONDS", 1.0)
+    monkeypatch.setattr(db_base, "_null_pool_session_limiter", None)
+    monkeypatch.setattr(db_base, "_null_pool_session_limiter_size", 0)
+    first_entered = asyncio.Event()
+    release_first = asyncio.Event()
+    second_entered = asyncio.Event()
+
+    async def first_session() -> None:
+        async with db_base._database_session_slot():
+            first_entered.set()
+            await release_first.wait()
+
+    async def second_session() -> None:
+        async with db_base._database_session_slot():
+            second_entered.set()
+
+    first_task = asyncio.create_task(first_session())
+    await first_entered.wait()
+    second_task = asyncio.create_task(second_session())
+    await asyncio.sleep(0)
+
+    assert second_entered.is_set() is False
+
+    release_first.set()
+    await asyncio.gather(first_task, second_task)
+    assert second_entered.is_set() is True
+
+
 @pytest.mark.asyncio
 async def test_init_db_serializes_bootstrap_ddl_with_advisory_lock(monkeypatch):
     from src.db import base as db_base