Session Model

Layers

L0 raw blob          content-addressed native bytes (import = snapshot)
L1 canonical log     unified envelope, append-only, single durable source of truth
L2 projections       read models, always rebuildable from the log

Hierarchy

Session ──1:N──> Run ──1:N──> Turn ──1:N──> Message ──> ordered ContentBlocks
                         └──> ToolCall / ToolResult

• Session — one conversation: nativeSessionId (harness-native) + id (content-addressed canonical id).
• Run — an execution unit (harnesses delimit run/turn differently).
• Turn — one user input → agent output.
• Message — role ∈ {system, user, assistant, tool, unknown} + ordered blocks.
• Tool — tool-call + tool-result pairing; the result lives on the tool entity, decoupled from message block shape.

Lineage DAG

Sessions are not a flat table:

relation { id, sourceSessionId, targetSessionId, type, typeData, createdAt }
type ∈ { fork, resume, handoff, subagent, compact }

handoff creates a new session + relation — it never masquerades as the same session, so provenance stays honest.

Identity & idempotency

• Event ids are content-addressed → re-import is idempotent.
• Session canonical id = sha256(harness ‖ native_session_id ‖ source_sha256) (length-prefixed, cross-harness collision-safe).
• Event ids are globally idempotent; replays deduplicate by eventId.

Full detail: asp/spec/overview.md and schema/agent-session-contracts.ts.