Channels, messages, and conversations

Channel identity and policy

A channel is identified by channelTypeKey plus channelId inside one application environment. The channel type defines authorization and capability policy. Membership, creator, and authenticated-user rules are evaluated server-side for each operation and subscription.

Messages and direct threads

• Top-level message creation uses a caller-generated fixed message identity for safe reconciliation.
• Message edits use expected versions to reject stale conflicting updates.
• Top-level history excludes direct replies; thread reads return a coherent root and reply page.
• Reactions have an independently versioned summary and a bounded exact-type reactor list.
• Deleted entities leave scoped tombstones where clients need deterministic cache reconciliation.

Conversations and read horizons

Conversation and unread views are private projections for the authenticated app user. A mark-read operation advances a monotonic channel or thread horizon. Projection delivery may lag the mutation briefly, so clients merge by independent version and refresh on conflict or gap.

Pagination and search

Changing collections use cursor pagination with a stable unique tie-breaker. Cursors are opaque and scope-bound. Query and search inputs are allowlisted, bounded, and compiled into resource-specific filters; never pass database operators or invent cursors.