[Bug]: Packaged server logs an ERROR traceback at every start because optional spacy is missing #1789

Describe the bug

Every server start on a packaged install logs ERROR Decomposer import FAILED with a full ModuleNotFoundError: No module named 'spacy' traceback.

spacy is deliberately kept out of memmachine-server's dependencies; it lives only in the root multihop dependency group, so no pip install has it. rarag_query_agent.py:39-41 handles the ImportError correctly by falling back, but logs it with logger.exception. New since v0.3.9 (#1477).

Steps to reproduce

uv build --project packages/server   # at tag 0.4.0-rc1
pip install memmachine_server-0.4.0rc1-py3-none-any.whl
python -c "import memmachine_server.retrieval_agent.agents.rarag_query_agent"
# ERROR Decomposer import FAILED + traceback (same on memmachine-server startup)

Expected behavior

An optional dependency that is absent by design logs one INFO/WARNING line, such as "multi-hop decomposer disabled; install with uv sync --group multihop", not an ERROR with a traceback.

Environment

• MemMachine Version: 0.4.0-rc1 (ad8ff24)
• OS: Ubuntu, Python 3.12