Create a provider for Vercel AI Gateway
## Summary
Create a new AI provider for the [Vercel AI Gateway](https://vercel.com/ai-gateway) so Drupal sites can route AI requests through Vercel's unified gateway endpoint.
## What is Vercel AI Gateway?
Vercel AI Gateway is a unified API that gives access to hundreds of AI models (text, image, and video) from providers such as OpenAI, Anthropic, xAI, Google, and others through a **single endpoint** — without managing a separate API key per provider.
Key features relevant to a Drupal provider:
- **Unified access** — one endpoint, one API key, many providers/models.
- **Automatic failover** — requests stay up when an individual model/provider has an outage.
- **Observability** — centralized dashboard for token usage, spend, and request details.
- **Transparent pricing** — upstream provider list price with no markup; supports Vercel billing or bring-your-own-keys.
- **API compatibility** — supports the OpenAI Chat Completions and Anthropic Messages formats, plus the Vercel AI SDK.
## Proposed resolution
Build an AI module provider plugin for Vercel AI Gateway:
- Authenticate with a Vercel AI Gateway API key.
- Use the OpenAI-compatible endpoint so it can reuse existing chat/embeddings normalization where possible (model names are specified as `provider/model`, e.g. `openai/gpt-5.5`).
- Implement the relevant operation types (chat, embeddings, and image/video where supported by the gateway).
- Support model discovery / configuration of the model list.
- Map token usage from the gateway response into the AI module's `TokenUsageDto`.
## Remaining tasks
- [ ] Confirm which operation types the gateway exposes and which to support first (chat as MVP).
- [ ] Decide whether to ship as a standalone contrib provider module or as a submodule.
- [ ] Implement and test the provider plugin.
## References
- Vercel AI Gateway: https://vercel.com/ai-gateway
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