Create an eval suite (author-only, does not run)

Creates a runnable eval suite — the suite record plus its test cases — and responds 201 synchronously, WITHOUT executing anything. Use this to author a suite, then run it later with POST /eval-runs (passing the returned suiteId).

This is distinct from POST /eval-runs, which creates a run and detaches execution, responding 202 with a runId. There is no concurrency cap here (no run is started).

The body uses an ergonomic authoring shape: a suite-level default model (and optional provider) applies to every test unless the test overrides it; provider is derived from a provider/model id when neither is supplied. Each test's case body is an ordered steps array (prompt / toolCall / interact / assert).

Guest callers are denied (suite creation is a write).