Harden ingestion and graph serialization reliability paths

[cursor]

Summary

• Refactored ingestion text extraction into a reusable Strategy + Factory component in src/core/ingestion/text_strategy.py.
• Updated ingest_data to use a single extracted payload text path for chunk storage, observation generation, and KG enrichment.
• Fixed second-degree graph hop vector assembly by introducing reusable helpers in GraphAdapter and removing brittle duplicated node-description lookups.
• Hardened Neo4j graph operation result serialization with typed fallbacks and warning logs instead of broad silent exception handling.
• Stabilized architecture tests by extending module stubs required by controller imports.
• Added focused reliability tests in tests/test_reliability_refactors.py for ingestion strategy behavior, graph neighbor vector assembly, and serializer fallback behavior.

Validation

• Ran full test suite with unittest discovery:
  • python3 -m unittest discover -s tests -p "test_*.py"
  • Result: Ran 51 tests ... OK

Notes

• During validation in this environment, missing local runtime test dependencies were installed to execute tests (pytest, pydantic, httpx, python-dotenv, starlette, fastapi).
• Source code changes were committed and pushed in incremental commits on cursor/codebase-structural-improvements-a26f.