Draft PRD for a unified, versioned audit-event envelope with a
trusted/untrusted field split, canonical JSON + per-writer hash chain,
an append-only JSONL journal as source of truth, a rebuildable SQLite
index for local query, and an initial event registry. Scheduled to land
immediately after the host controller (#468), which becomes its first
producer.
Refs #487
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
