Chains

Chain composes three chainlets: transcribe (audio→text), summarize (text→summary), translate (summary→localized). Operator returns dict from transcribe instead of the declared TranscribeOutput pydantic model.

Each chainlet declares typed inputs and outputs (pydantic models). The Chains runtime validates at the hop boundary; returning an untyped dict triggers a schema-mismatch failure at the next hop. Declare the model and import it from a shared package consumed by both chainlets.

Client calls POST /chains/{chain_id}/run with the entrypoint chainlet's input shape. Response is the terminal chainlet's output plus a per-chainlet trace.

Address the chain via its chain_id (not by stringing predict calls across the constituent chainlet URLs — that bypasses the Chains runtime's tracing and error contract). Surface the per-chainlet trace to the operator's observability store for replay.

Chainlet 2 of 3 raises an exception. The runtime returns a chain-level failure response with the offending chainlet's name and stack location.

Surface chain-level failures with chainlet identity (which hop failed) and the upstream chainlets' outputs where present, so the operator can resume from the failure point instead of replaying the whole graph. Honor [REQUIRES-VERIFICATION] for the exact partial-output contract.