[wemeetagain]

Summary

• extract the reusable SigningRequest union and add a GENERIC signing request
• add an optional same-duty, multi-key batch signing endpoint with ordered per-key results
• add an optional distributed-signing profile for participant discovery, partial signing, and batch partial signing
• document threshold recovery, authorization, and slashing-protection requirements, with a deterministic 2-of-3 test vector

Motivation

The existing API standardizes the validator-client-to-signer boundary, but threshold deployments also need a consistent coordinator-to-participant boundary. This adds that profile without changing the existing full-signature endpoint or requiring distributed-signing details in validator clients.

This also addresses the generic-signing and batching use cases discussed in #26 and #19 while keeping them additive to the existing API.

API additions

• POST /api/v1/eth2/sign for same-duty multi-key batch signing
• GET /api/v1/eth2/distributed/accounts
• GET /api/v1/eth2/distributed/accounts/{identifier}
• POST /api/v1/eth2/distributed/sign
• POST /api/v1/eth2/distributed/sign/{identifier}

The existing POST /api/v1/eth2/sign/{identifier} endpoint remains the full-signature endpoint. Distributed signing endpoints return partial signatures and participant metadata only.

Compatibility and release note

All new request types and endpoints are additive. The specification version is intentionally unchanged because #28 currently claims v1.4.0; once that work lands, this branch can be rebased and its new signing types incorporated into the centralized SigningRequest union.

Validation

• Spectral lint: zero errors; one pre-existing /publicKeys camel-case warning
• Swagger CLI validation and fully dereferenced bundle generation
• JSON syntax validation for the threshold-signing vector
• verified every 2-of-3 recovery subset in the threshold vector against the parent implementation's conformance suite
• git diff --check

Related: #19, #26