feat(extensions): add MongoDB session backend

pyproject.toml

@@ -44,6 +44,7 @@ sqlalchemy = ["SQLAlchemy>=2.0", "asyncpg>=0.29.0"]
 encrypt = ["cryptography>=45.0, <46"]
 redis = ["redis>=7"]
 dapr = ["dapr>=1.16.0", "grpcio>=1.60.0"]
+mongodb = ["pymongo>=4.14"]
 docker = ["docker>=6.1"]
 blaxel = ["blaxel>=0.2.50", "aiohttp>=3.12,<4"]
 daytona = ["daytona>=0.155.0"]
@@ -90,6 +91,7 @@ dev = [
   "grpcio>=1.60.0",
   "testcontainers==4.12.0",       # pinned to 4.12.0 because 4.13.0 has a warning bug in wait_for_logs, see https://github.com/testcontainers/testcontainers-python/issues/874
   "pyright==1.1.408",
+  "pymongo>=4.14",
 ]
 
 [tool.uv.workspace]

src/agents/extensions/memory/__init__.py

@@ -19,6 +19,7 @@
         DaprSession,
     )
     from .encrypt_session import EncryptedSession
+    from .mongodb_session import MongoDBSession
     from .redis_session import RedisSession
     from .sqlalchemy_session import SQLAlchemySession
 
@@ -29,6 +30,7 @@
     "DAPR_CONSISTENCY_STRONG",
     "DaprSession",
     "EncryptedSession",
+    "MongoDBSession",
     "RedisSession",
     "SQLAlchemySession",
 ]
@@ -117,4 +119,15 @@ def __getattr__(name: str) -> Any:
                 "Install it with: pip install openai-agents[dapr]"
             ) from e
 
+    if name == "MongoDBSession":
+        try:
+            from .mongodb_session import MongoDBSession  # noqa: F401
+
+            return MongoDBSession
+        except ModuleNotFoundError as e:
+            raise ImportError(
+                "MongoDBSession requires the 'mongodb' extra. "
+                "Install it with: pip install openai-agents[mongodb]"
+            ) from e
+
     raise AttributeError(f"module {__name__} has no attribute {name}")