EncryptedSession limit can return fewer valid items when latest envelopes are invalid

[Aphroq]

Please read this first

• Have you read the docs? Yes.
• Have you searched for related issues? Yes.

Describe the bug

EncryptedSession.get_items(limit=N) applies limit to the underlying encrypted envelopes before it decrypts them. Invalid, expired, or otherwise undecryptable envelopes are then dropped, so a latest invalid envelope can hide earlier valid context even when enough valid items exist in the session history.

I searched existing issues and PRs for EncryptedSession get_items limit, EncryptedSession invalid token limit, and encrypted session expired limit, and did not find a direct match.

This is specific to EncryptedSession because it wraps another session backend and filters encrypted envelopes after reading them. The adjacent negative limit behavior is a separate session-limit consistency issue and is not part of this report.

Debug information

• Agents SDK version: v0.16.0 / current main at eed9100
• Python version: Python 3.12.1
• Backend: EncryptedSession wrapping SQLiteSession

Repro steps

Run this script against an affected version:

import asyncio

from cryptography.fernet import Fernet

from agents import SQLiteSession
from agents.extensions.memory.encrypt_session import EncryptedSession


async def main() -> None:
    session_id = "encrypted-limit-repro"
    underlying_session = SQLiteSession(session_id)
    encrypted_session = EncryptedSession(
        session_id=session_id,
        underlying_session=underlying_session,
        encryption_key=Fernet.generate_key().decode("utf-8"),
    )

    try:
        await encrypted_session.add_items([{"role": "user", "content": "older valid"}])
        await underlying_session.add_items(
            [{"__enc__": 1, "v": 1, "kid": "hkdf-v1", "payload": "not-a-valid-token"}]
        )

        all_items = await encrypted_session.get_items()
        limited_items = await encrypted_session.get_items(limit=1)

        print("all:", [item.get("content") for item in all_items])
        print("limit=1:", [item.get("content") for item in limited_items])

        assert [item.get("content") for item in all_items] == ["older valid"]
        assert [item.get("content") for item in limited_items] == ["older valid"]
    finally:
        underlying_session.close()


asyncio.run(main())

On affected versions, the output is:

all: ['older valid']
limit=1: []

The first assertion passes, but the second assertion fails because limited_items is empty.

Expected behavior

For positive explicit limits, EncryptedSession.get_items(limit=N) should return the latest N valid decrypted items when that many valid items exist in the underlying history. Invalid, expired, or otherwise undecryptable envelopes should not count against the requested limit.