chore: import upstream snapshot with attribution

tests/utils/simple_session.py

@@ -0,0 +1,82 @@
+from __future__ import annotations
+
+from typing import cast
+
+from agents.items import TResponseInputItem
+from agents.memory.session import Session
+from agents.memory.session_settings import SessionSettings
+
+
+class SimpleListSession(Session):
+    """A minimal in-memory session implementation for tests."""
+
+    session_settings: SessionSettings | None = None
+
+    def __init__(
+        self,
+        session_id: str = "test",
+        history: list[TResponseInputItem] | None = None,
+    ) -> None:
+        self.session_id = session_id
+        self._items: list[TResponseInputItem] = list(history) if history else []
+        # Some session implementations strip IDs on write; tests can opt-in via attribute.
+        self._ignore_ids_for_matching = False
+        # Mirror saved_items used by some tests for inspection.
+        self.saved_items: list[TResponseInputItem] = self._items
+
+    async def get_items(self, limit: int | None = None) -> list[TResponseInputItem]:
+        if limit is None:
+            return list(self._items)
+        if limit <= 0:
+            return []
+        return self._items[-limit:]
+
+    async def add_items(self, items: list[TResponseInputItem]) -> None:
+        self._items.extend(items)
+
+    async def pop_item(self) -> TResponseInputItem | None:
+        if not self._items:
+            return None
+        return self._items.pop()
+
+    async def clear_session(self) -> None:
+        self._items.clear()
+
+
+class CountingSession(SimpleListSession):
+    """Session that tracks how many times pop_item is invoked (for rewind tests)."""
+
+    def __init__(
+        self,
+        session_id: str = "test",
+        history: list[TResponseInputItem] | None = None,
+    ) -> None:
+        super().__init__(session_id=session_id, history=history)
+        self.pop_calls = 0
+
+    async def pop_item(self) -> TResponseInputItem | None:
+        self.pop_calls += 1
+        return await super().pop_item()
+
+
+class IdStrippingSession(CountingSession):
+    """Session that strips IDs on add to mimic hosted stores that reassign IDs."""
+
+    def __init__(
+        self,
+        session_id: str = "test",
+        history: list[TResponseInputItem] | None = None,
+    ) -> None:
+        super().__init__(session_id=session_id, history=history)
+        self._ignore_ids_for_matching = True
+
+    async def add_items(self, items: list[TResponseInputItem]) -> None:
+        sanitized: list[TResponseInputItem] = []
+        for item in items:
+            if isinstance(item, dict):
+                clean = dict(item)
+                clean.pop("id", None)
+                sanitized.append(cast(TResponseInputItem, clean))
+            else:
+                sanitized.append(item)
+        await super().add_items(sanitized)