Problem
Existing Cascade KBs (cascade-research, cascade-timeline, cascade-solidarity) must continue working after the refactor. Frontmatter in existing markdown files must be forward-compatible. If journalism-investigation adds new required fields, existing entries must not fail validation.
Scope
Audit all journalism-investigation field additions for backward compatibility
New fields must have sensible defaults (e.g., `verification_status` defaults to `unverified`)
Schema migration: if any field names change, add migration in Cascade's migration.py
Test: load all 3 existing Cascade KB types, verify zero validation errors
Document migration path for users upgrading CascadeAcceptance Criteria
Existing Cascade KBs load without errors after refactor
No manual frontmatter changes required
Schema migration handles any field renames automatically
`pyrite qa validate` passes on existing Cascade data