Handoff

Handoff

Cheap-tier first; escalate to a deep tier via agent.handoff when the cheap model's confidence drops below threshold.

Before ARCP

Routing layers either burn the most expensive model on every call, or shard by a static rule (regex on the prompt) and silently mis-route hard requests to the cheap path. Conversation context gets POSTed across as a JSON blob with no integrity check, no trace propagation, and no runtime verification.

With ARCP

let ref = try await packageContext(cheap, transcript: ...)   // artifact.put
try await emitHandoff(cheap, artifactRef: ref, traceId: traceId)

The deep runtime is identified by kind + pinned fingerprint; mismatch = refuse. Context rides as an artifact_id, not an inline blob — sha256 + media_type included.

ARCP primitives

• Capability negotiation distinguishes the tiers — RFC §7.
• agent.handoff + runtime identity verification — §14, §8.3.
• Artifacts for transcript transfer — §16.
• Trace propagation across the handoff — §17.1.

File tour

• Sources/Handoff/main.swift — open cheap (pinned), ask, escalate if needed.
• Sources/Handoff/Cheap.swift — attempt stub + ARCPClient.placeholder.

Variations

• Three tiers (haiku → sonnet → opus) with two thresholds.
• Sticky-handoff cache keyed on a request fingerprint so repeated hard prompts skip the cheap pass.
• Deep tier holds the session; cheap closes immediately after emitting the handoff (current shape) — or both stay open for back-and-forth.