test: add Session/Memory/Summary replay consistency harness

tests/sessions/DESIGN.md

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+# 回放一致性框架设计说明
+
+框架以 Python fixture 描述统一轨迹，默认驱动 InMemory 与 SQLite Session/Memory；`REPLAY_MODE=inmemory` 可只跑内存，integration 可用环境变量接入外部 SQL，Redis 未配置时跳过。
+
+比较前递归排序字典，过滤空 Part，并归一化自动 UUID、时间戳和空集合；session id、事件顺序、state、工具参数及 memory 内容仍精确比较。`allowed_diff` 必须限定后端对、完整字段路径并写明原因，禁止宽泛忽略。
+
+Summary 使用确定性 Mock 生成；harness 将文本、版本、更新时间、压缩计数和 session 归属写入 summary anchor metadata，再从各后端回读。文本仅做 Unicode 与空白归一化，版本、归属和覆盖关系严格比较。报告记录 case、后端、session id、event index/summary id、字段路径及双方值。

tests/sessions/conftest.py

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+# Tencent is pleased to support the open source community by making tRPC-Agent-Python available.
+#
+# Copyright (C) 2026 Tencent. All rights reserved.
+#
+# tRPC-Agent-Python is licensed under Apache-2.0.
+"""Pytest fixtures for replay consistency testing.
+
+每个 fixture 对应一个 replay case，测试类通过 fixture 名称引用。
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from .replay_cases import (
+    ReplayCase,
+    build_single_turn_text,
+    build_multi_turn_text,
+    build_tool_call_response,
+    build_state_basic_update,
+    build_state_three_tier,
+    build_memory_store_search,
+    build_memory_multi_session,
+    build_summary_generation,
+    build_summary_truncation,
+    build_summary_error_detection,
+    build_error_duplicate_write,
+)
+
+
+@pytest.fixture(scope="module")
+def case_single_turn_text() -> ReplayCase:
+    return build_single_turn_text()
+
+
+@pytest.fixture(scope="module")
+def case_multi_turn_text() -> ReplayCase:
+    return build_multi_turn_text()
+
+
+@pytest.fixture(scope="module")
+def case_tool_call_response() -> ReplayCase:
+    return build_tool_call_response()
+
+
+@pytest.fixture(scope="module")
+def case_state_basic_update() -> ReplayCase:
+    return build_state_basic_update()
+
+
+@pytest.fixture(scope="module")
+def case_state_three_tier() -> ReplayCase:
+    return build_state_three_tier()
+
+
+@pytest.fixture(scope="module")
+def case_memory_store_search() -> ReplayCase:
+    return build_memory_store_search()
+
+
+@pytest.fixture(scope="module")
+def case_memory_multi_session() -> ReplayCase:
+    return build_memory_multi_session()
+
+
+@pytest.fixture(scope="module")
+def case_summary_generation() -> ReplayCase:
+    return build_summary_generation()
+
+
+@pytest.fixture(scope="module")
+def case_summary_truncation() -> ReplayCase:
+    return build_summary_truncation()
+
+
+@pytest.fixture(scope="module")
+def case_summary_error_detection() -> ReplayCase:
+    return build_summary_error_detection()
+
+
+@pytest.fixture(scope="module")
+def case_error_duplicate_write() -> ReplayCase:
+    return build_error_duplicate_write()