Problem
The 4 write-tier MCP tools (investigation_create_entity, investigation_create_event, investigation_create_claim, investigation_log_source) are tested for schema and registration but have never been executed against a real DB. The handlers create entries via KBService but no integration test verifies the full round-trip: create via write tool, query back via read tool.
Scope
Add integration tests that:
1. Set up a temporary KB with the journalism-investigation preset
2. Create entries via each write-tier tool handler
3. Query them back via the corresponding read-tier tool handler
4. Verify data integrity through the full round-trip
Test Cases
Create entity via write tool, find it via investigation_entities
Create event via write tool, find it via investigation_timeline
Create claim via write tool, find it via investigation_claims
Log source via write tool, find it via investigation_sources
Create claim with evidence refs, trace via investigation_evidence_chain
Verify deduplication warnings (create same-title entity twice)
Verify validation errors (create entity with invalid type)
Verify claim created without evidence produces warningAcceptance Criteria
All 4 write tools tested with real DB round-trip
Error cases tested (invalid types, missing required fields)
Warning cases tested (no evidence on claim, duplicate entity)
Tests use tmp_path fixture, no persistent state