Phase 3-5 of ActivityPub integration: - Federation handlers: post.published, calendar_entry.created, product.listed → publish_activity() for AP outbox - AP delivery handler: federation.activity_created → sign + POST to follower inboxes with HTTP Signatures - IPFS storage wired into publish_activity() (best-effort) - Anchoring utility: merkle trees + OpenTimestamps Bitcoin timestamping Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>