Plan record with version history.
Compliance requirement for regulated environments (banks, DATEV):
every plan revision must be preserved for audit trail.
current: the active plan version
history: all previous versions (newest first)
reviewFindings: independent review findings per iteration (parallel, NOT mixed)
Plan record with version history. Compliance requirement for regulated environments (banks, DATEV): every plan revision must be preserved for audit trail.
Architecture invariant: plan.history = author artifacts, plan.reviewFindings = reviewer artifacts