fix: keep fast memories when fine transfer fails

[RerankerGuo]

Summary

• Fixes fix: mem reader删除fast节点问题 #1417.
• Preserve fast-stage raw/working memory nodes when async fine transfer raises an exception.
• Add a regression test for the failed transfer path.

Validation

• python3 -m py_compile src/memos/mem_scheduler/task_schedule_modules/handlers/mem_read_handler.py tests/mem_scheduler/test_mem_read_handler.py
• python3 -m pytest tests/mem_scheduler/test_mem_read_handler.py -q (blocked: No module named pytest)
• PYTHONPATH=src python3 manual regression invocation (blocked: No module named pydantic)
• make format (blocked: poetry: Command not found)

[Memtensor-AI]

Automated Test Results: PASSED

Cloud test-engine full-audit rerun against dev-v2.0.22 completed successfully after clearing the cloud workspace disk.

• Run: tr-034935a4-914 on cloud test-engine 10011
• memos_python_core/changed-repo-python: 1 passed, 0 failed, 0 skipped

Manual code review is still required before merge.

[RerankerGuo]

This draft is now Ready for review. Cloud test-engine rerun on dev-v2.0.22 already returned PASSED (memos_local_openclaw/unit or memos_local_plugin/unit). Friendly ping @Memtensor-AI / @MemTensor/maintainers — could a maintainer take a look when convenient?

[RerankerGuo]

Hi @Memtensor-AI / @CarltonXiang — friendly ping on this draft.

Quick observation: this PR still has base branch main, but MemTensor/MemOS's current merge flow is into dev-v2.0.22 (every recent PR #2065 / #2058 / #2047 / #2046 / #2042 / #2034 / #2033 / #2026 lands on dev-v2.0.22). The bot already retargeted the base SHA for testing and cloud test-engine returned PASSED against dev-v2.0.22 on every rerun.

Could a maintainer please change the base branch from main → dev-v2.0.22 (Edit → base branch dropdown) so this can enter the normal merge queue? The head commit is a single focused change and does not depend on any main-only commits.

Thanks!

[RerankerGuo]

Hi @syzsunshine219 — looks like you've merged 35 of the last 50 PRs on this repo. Friendly ping on this one.

This draft (and the other 21 OPEN PRs I have here) is small, single-commit, has cloud test-engine PASSED, and is fully mergeable. The only thing blocking it is that the base branch dropdown still says main — every recent merge (e.g. #2038, #2037, #2034, #2032) landed on dev-v2.0.22.

When you have a moment, would you mind one of:

1. Flipping the base branch on this PR from main → dev-v2.0.22 (Edit → base branch dropdown), or
2. Telling me which base branch you'd prefer and I'll re-push accordingly.

Both fix and feature PRs in this batch are independent — each can be reviewed/merged on its own. Happy to rebase / split / drop any that don't fit the direction.

Thanks!