Incremental sync

Cursor-based incremental sync endpoint for offline-first SDK clients. Returns events that occurred after the given cursor. Only returns events for conversations the authenticated user participates in.

Event types:

• message.new — New message sent
• message.edit — Message content edited
• message.delete — Message deleted
• conversation.create — Direct or group conversation created
• conversation.update — Conversation title/description changed
• conversation.archive — Conversation archived
• participant.add — Member added to conversation
• participant.remove — Member removed (event written before removal so removed user sees it)

Sync flow:

1. On first connect, call with since=0 to get initial events
2. Store the returned cursor locally
3. On reconnect or periodic poll, call with since={cursor}
4. If hasMore is true, keep fetching with updated cursor

Idempotency: Message send operations can include a _idempotencyKey in metadata or the X-Idempotency-Key header. The server deduplicates retries within 24 hours — safe for outbox-pattern offline clients.