Add Alembic migration m4_002_skill_flattened_tools to extend the skills
table with five new columns: flattened_tools_json, includes_json,
capability_summary_json, yaml_text, and flattening_hash (SHA-256). A
defence-in-depth uniqueness constraint (uq_skills_name) is also added.
Update SkillModel with the new column definitions and extend
SkillRepository with update_flattened_tools(), get_flattened_tools(),
needs_refresh(), recompute_flattening_hash(), and
invalidate_cached_summaries() methods. The existing update() method
now nulls all cached fields on mutation (hash-based invalidation).
All new repository methods follow the session-factory pattern with
@database_retry and flush-but-don-t-commit semantics. Structured
logging via structlog records cache updates and invalidations.
Database schema docs updated with the new skills table columns and a
persistence-field-to-domain-model mapping table.
Tests:
- 6 Behave scenarios covering create, invalidation, hash staleness,
refresh recomputation, uniqueness constraint, and namespace filtering
- 2 Robot Framework smoke tests (round-trip and invalidation)
- 3 ASV benchmarks (persist, refresh check, namespace list)
ISSUES CLOSED: #166
