fix(storages): handle serialized role strings in Mem0Storage message preparation

[Wenyan0315]

Related Issue

Closes #4389

Description

Mem0Storage._prepare_messages reads .value off record["role_at_backend"], but MemoryRecord.to_dict() — the only in-tree producer of these dicts — serializes that field to a plain string. Every save() therefore raises AttributeError, which is swallowed by the blanket except Exception, so MemoryClient.add is never called and nothing is persisted.

The fix makes _prepare_messages accept both forms: it unwraps .value when the field is an OpenAIBackendRole and passes strings through as-is.

The existing test_save never caught this because it injects the enum object directly, bypassing the to_dict()\) serialization path that real callers (e.g. ChatHistoryMemory) go through. This PR adds test_save_with_serialized_records, which builds records through MemoryRecord.to_dict()`; it fails on the unfixed code and passes with the fix.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Checklist

• I have read and agree to the AI-Generated Code Policy (required)
• I have linked this PR to an issue (required)
• I have checked if any dependencies need to be added or updated in pyproject.toml and run uv lock
• I have updated the tests accordingly (required for a bug fix or a new feature)
• I have updated the documentation if needed
• I have added examples if this is a new feature

Test output

$ python -m pytest test/storages/key_value_storages/test_mem0_cloud.py -v

test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_clear PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_error_handling_clear PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_error_handling_load PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_error_handling_save PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_initialization PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_initialization_required_agent_id PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_integration SKIPPED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load_with_both_agent_and_user_id PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load_with_missing_metadata_key PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load_with_no_filters PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load_with_none_metadata PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_load_with_only_agent_id PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_prepare_messages PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_save PASSED
test/storages/key_value_storages/test_mem0_cloud.py::TestMem0Storage::test_save_with_serialized_records PASSED

======================== 15 passed, 1 skipped in 0.47s =========================

The new test_save_with_serialized_records was also verified to fail against the unfixed code (stashed-fix A/B check), confirming it is a true regression test.

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[Wenyan0315]

CI triage for head 8ce1e091b3f6ed3f6cb5a8cb6b3b4d3439b627bc (AI-assisted; checked against the failed-job logs and workflow definitions):

• Package tests: all three jobs (fast, llm, very_slow) stop during collection with the same five credential errors: test_chat_agent, test_knowledge_agent, test_role_playing, test_agent_mcp_server, and test_function_tool_decorator. Logs report missing OPENAI_API_KEY / missing OpenAI credentials; these runs do not establish whether the Mem0 regression test passes in CI.
• Examples and apps: examples stop during collection of test_role_description_example for the missing key. Apps finish with 7 passed, 1 skipped, and 1 failed (test_session), also for the missing key.
• Label automation: the issues.addLabels request returns HTTP 403, Resource not accessible by integration.

The package workflow uses the repository OpenAI secret on pull_request, and label automation uses GITHUB_TOKEN. The observed failures are consistent with fork-PR secret/token restrictions. No code/test changes are proposed to work around them; a maintainer will need to use the project's approved CI path or assess these environmental checks. Pre-commit, minimal dependencies, dependency review, and CodeQL passed.

This is log-based triage, not a fresh test rerun or a claim that the full suite passes. The existing focused local test result remains recorded in the PR description.

[chrikrah]

@Wenyan0315, approving at 8ce1e09. This fixes #4389 on the path I reported it from: ChatHistoryMemory over Mem0Storage now reaches MemoryClient.add.

$ pytest -q test/storages/key_value_storages/test_mem0_cloud.py
# 8ce1e09 (head), mem0ai 2.0.11 as in uv.lock
15 passed, 1 skipped in 2.49s
# head tests, mem0_cloud.py restored from 24fde60 (the PR's base)
FAILED ...TestMem0Storage::test_save_with_serialized_records
E   AssertionError: Expected 'add' to have been called once. Called 0 times.
1 failed, 14 passed, 1 skipped in 2.20s

$ python camel_probe.py   # ChatHistoryMemory(storage=Mem0Storage), patched MemoryClient, one write_record()
# 8ce1e09
MemoryClient.add calls: 1 [{'role': 'user', 'content': 'remember this'}]
# 24fde60
ERROR - Error adding memory: 'str' object has no attribute 'value'
MemoryClient.add calls: 0
# not run: a live Mem0 account

@fengju0213, could you merge this one when you get to it?