Model discovery currently assumes every provider exposes all models via
GET {baseURL}/models. Providers like Alibaba Cloud Bailian serve video,
3D and some image models through dedicated endpoints, so 21 models across
5 families (HappyHorse / Wan / Kling / PixVerse / Vidu / Tripo) are never
discoverable - a functional blocker for a video creation workbench.
This introduces a ModelDiscovery plugin interface with a registry that
matches vendor plugins by base URL and falls back to the standard OpenAI
implementation, keeping core discovery logic vendor-agnostic.
- add provider.ModelDiscovery interface and plugin registry
- add openai plugin (standard behaviour, default fallback)
- add bailian plugin (standard + 21 extended multimodal models)
- gate behind ENABLE_PROVIDER_PLUGINS, default false
- register plugins lazily from service layer to avoid import cycle
Verified locally: flag off -> 238 models (unchanged); flag on -> 257
models (238 + 19 net new after dedup). OpenAI and Gemini channels
unaffected in both modes.
