Adds OpenAPISpec::from_yaml and OpenAPISpec::from_str alongside the
existing from_json. from_str is JSON-first, YAML-fallback (ADR-051 §2):
a valid JSON doc parses through serde_json (stricter grammar, immune to
YAML-specific coercion); only on JSON failure does it fall back to the
YAML parser. yaml_serde 0.10 (resolves to 0.10.4, latest stable) is the
maintained official-YAML-org fork of the deprecated serde_yaml; not
feature-gated per ADR-051 §3 (YAML OpenAPI is first-class).
Note: ADR-051 §2's stated YAML 1.1 boolean-coercion rationale does not
hold for yaml_serde 0.10 (YAML 1.2 core schema — yes/no/on/off are
strings). The JSON-first rule is retained per the Accepted ADR as a
defensive default; tests document the actual 0.10.x behavior with
explicit comments. The ADR rationale should be amended separately.
256 tests pass; clippy + fmt clean.
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.