from_openapi's spec already stated the contract as "JSON/YAML doc" but the
implementation only delivered the JSON half. vast.ai publishes a YAML
OpenAPI schema, which surfaces the gap. This is gap-filling against an
existing constraint — no architecture invariants touched (OpenAPISpec
stays serde_json::Value-based, forwarding handler / no-env-vars / error
fidelity / to_openapi output unchanged).
ADR-051 records: (1) from_yaml + format-detecting from_str constructors;
(2) JSON-first/YAML-fallback detection as a correctness rule (YAML 1.1
coerces yes/no/on/off to booleans — running JSON through YAML would
silently corrupt string fields); (3) yaml_serde dependency (maintained
official-YAML-org fork of deprecated serde_yaml, not feature-gated);
(4) to_openapi output stays JSON (scope boundary).
Specs updated to reference ADR-051 by number (http-adapters, overview,
both README ADR tables). Implementation task added at
tasks/http/adapters/from-openapi-yaml-input.md.