skilltest-core — the library that powers the skilltest CLI and, through
it, the language SDKs and test-framework packages.
The flow is: load a [Config] and one or more [TestCase]s, build a
[Provider] (the boundary to oneharness / a model), and hand both to a
[Runner], which drives each case into a conversation, scores the transcript
with natural-language [Eval]s, and returns a [Report]. The report's JSON
form is the stable contract the language SDKs consume.
Everything that crosses a trust boundary — config files, test-case YAML, skill frontmatter, and every provider response — is parsed into a typed model before use.