session_source Fork

session_source is a member-level OpenRig field that declares how a newly-launched managed seat should derive its initial conversation continuity from a prior runtime conversation source.

v1 supports one mode: fork, start a new managed seat from a prior native runtime conversation source without claiming the original seat continued.

The schema is runtime-neutral; implementation is runtime-specific (Claude and Codex have their own native fork commands).

Use this when

• Authoring a rig spec member that should fork from a prior session
• Authoring a rig expand payload with session_source
• Reasoning about whether to use fork vs rebuild vs resume vs fresh for a new seat
• Composing fork + handover (seat-handover-over-fork), see seat-continuity-and-handover skill

Don't use this when

• The seat is being restored, not created. Restore continues an existing managed seat. Fork creates a new seat.
• The continuity is artifact-backed mental-model rebuild (packet-derived understanding, not native runtime continuity). Use mode: rebuild (see seat-continuity-and-handover for the rebuild surface), do NOT collapse fork into artifact-backed reentry; the distinction is load-bearing.
• The runtime is terminal. Terminal runtime rejects session_source.

The shape (canonical YAML)

members:
  - id: reviewer-2
    runtime: claude-code        # or "codex"; not valid on terminal
    agent_ref: specs/agents/reviewer.yaml
    profile: reviewer
    cwd: .
    session_source:
      mode: fork
      ref:
        kind: native_id          # v1 fork mode supports native_id only
        value: "0b0165d7-cb4d-4650-90de-15c0a1ede9e6"