The 15-provider test hard-coded exact model IDs (gpt-5.3-codex-spark,
etc.) which depend on the external codex CLI's model/list endpoint.
Replace with structural checks: all IDs in gpt- family, at least one
codex-optimized model, and all models have required fields.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>