From a4ce73785bb6c024b6b8690cfbc0b15f2ca7c6a5 Mon Sep 17 00:00:00 2001
From: HughhhhCoder <hughz926@gmail.com>
Date: Wed, 2 Sep 2026 19:24:24 +0800
Subject: [PATCH 1/2] fix(memory): merge base session settings into subclasses

---
 src/agents/memory/session_settings.py |  6 ++++--
 tests/memory/test_session.py          | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/agents/memory/session_settings.py b/src/agents/memory/session_settings.py
index eb42f617f2..6f2ee60116 100644
--- a/src/agents/memory/session_settings.py
+++ b/src/agents/memory/session_settings.py
@@ -51,10 +51,10 @@ def resolve(self, override: SessionSettings | dict[str, Any] | None) -> SessionS
         override = _coerce_session_settings(override, settings_type=type(self))
 
         changes = {
-            field.name: getattr(override, field.name)
+            field.name: getattr(override, field.name, None)
             for field in fields(self)
             if (override_fields is None or field.name in override_fields)
-            and getattr(override, field.name) is not None
+            and getattr(override, field.name, None) is not None
         }
 
         return replace(self, **changes)
@@ -76,6 +76,8 @@ def _coerce_session_settings(
     *,
     settings_type: type[SessionSettings],
 ) -> SessionSettings:
+    if isinstance(value, SessionSettings):
+        return value
     return coerce_dataclass_config(value, settings_type, parameter_name="session")
 
 
diff --git a/tests/memory/test_session.py b/tests/memory/test_session.py
index 9667c5b23c..0ccdabd654 100644
--- a/tests/memory/test_session.py
+++ b/tests/memory/test_session.py
@@ -962,6 +962,25 @@ async def test_session_settings_resolve():
     assert final_none.limit == 100
 
 
+def test_session_settings_resolve_accepts_base_override_for_subclass() -> None:
+    """A subclass can resolve settings produced by the base RunConfig type."""
+    from pydantic.dataclasses import dataclass
+
+    @dataclass
+    class TenantSessionSettings(SessionSettings):
+        tenant: str = "default"
+
+    base = TenantSessionSettings(limit=100, tenant="acme")
+    run_config = RunConfig(session_settings={"limit": 50})
+
+    final = base.resolve(run_config.session_settings)
+
+    assert isinstance(final, TenantSessionSettings)
+    assert final.limit == 50
+    assert final.tenant == "acme"
+    assert base.limit == 100
+
+
 @pytest.mark.asyncio
 async def test_runner_with_session_settings_override():
     """Test that RunConfig can override session's default settings."""

From 1cc89176df3dabc6679352ef5b8622d5fa4c2e92 Mon Sep 17 00:00:00 2001
From: HughhhhCoder <hughz926@gmail.com>
Date: Thu, 3 Sep 2026 18:51:51 +0800
Subject: [PATCH 2/2] fix(memory): reject incompatible session setting
 overrides

---
 src/agents/memory/session_settings.py |  7 ++++++-
 tests/memory/test_session.py          | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/agents/memory/session_settings.py b/src/agents/memory/session_settings.py
index 6f2ee60116..0389b8c1de 100644
--- a/src/agents/memory/session_settings.py
+++ b/src/agents/memory/session_settings.py
@@ -77,7 +77,12 @@ def _coerce_session_settings(
     settings_type: type[SessionSettings],
 ) -> SessionSettings:
     if isinstance(value, SessionSettings):
-        return value
+        if type(value) is SessionSettings or isinstance(value, settings_type):
+            return value
+        raise TypeError(
+            f"Session settings override must be SessionSettings or an instance of "
+            f"{settings_type.__name__}; got {type(value).__name__}"
+        )
     return coerce_dataclass_config(value, settings_type, parameter_name="session")
 
 
diff --git a/tests/memory/test_session.py b/tests/memory/test_session.py
index 0ccdabd654..4ff654bb73 100644
--- a/tests/memory/test_session.py
+++ b/tests/memory/test_session.py
@@ -981,6 +981,25 @@ class TenantSessionSettings(SessionSettings):
     assert base.limit == 100
 
 
+def test_session_settings_resolve_rejects_incompatible_subclass_override() -> None:
+    """A subclass must not silently discard fields from a sibling subclass."""
+    from pydantic.dataclasses import dataclass
+
+    @dataclass
+    class TenantSessionSettings(SessionSettings):
+        tenant: str = "default"
+
+    @dataclass
+    class RegionSessionSettings(SessionSettings):
+        region: str = "default"
+
+    base = TenantSessionSettings(limit=100, tenant="acme")
+    override = RegionSessionSettings(limit=50, region="us-east-1")
+
+    with pytest.raises(TypeError, match="TenantSessionSettings"):
+        base.resolve(override)
+
+
 @pytest.mark.asyncio
 async def test_runner_with_session_settings_override():
     """Test that RunConfig can override session's default settings."""