fix(workers-ai-provider): preserve structured output schema name

[slegarraga]

Summary

• wrap AI SDK structured-output schemas in the OpenAI-compatible json_schema envelope before sending them to Workers AI
• preserve Output.object({ name, description }) on the request body, defaulting the schema name to response when not provided
• add REST regression coverage for the request body sent by workers-ai-provider

Fixes #559.

Validation

• corepack pnpm --filter workers-ai-provider exec vitest --watch=false test/structured-output.test.ts
• corepack pnpm --filter workers-ai-provider type-check
• corepack pnpm --filter workers-ai-provider test:ci
• corepack pnpm exec oxfmt --check packages/workers-ai-provider/src/workersai-chat-language-model.ts packages/workers-ai-provider/test/structured-output.test.ts

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Latest commit: a406b61

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workers-ai-provider	Patch

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[threepointone]

Thanks for this, @slegarraga — your diagnosis of #559 was correct, and the request-body regression test was a great instinct (we ended up adding similar wire-shape assertions).

We've resolved #559 a different way, so I'm closing this as superseded. Two pieces landed:

• Partner models (openai/…) — feat(workers-ai-provider): route third-party models through AI Gateway (resumable streaming, fallback, BYOK) #573 (gateway delegate, in 3.2.0). Third-party catalog slugs now route through AI Gateway and the real @ai-sdk/* provider, which builds the response_format.json_schema.name envelope itself (opt in with createWorkersAI({ binding, providers: [openai] })). So the native code path no longer needs to construct that envelope.
• Native models (@cf/…) — fix(workers-ai-provider): preserve structured-output name/description on native models #576 (in 3.2.0). Here we intentionally did not wrap the schema in { name, schema }: native Workers AI expects a bare JSON Schema under json_schema, and wrapping it risks regressing native structured output (it'd be read as a schema with no type/properties). Instead we fold name → the schema's title and description → description, preserving the guidance while keeping a valid bare schema.

That's the main reason we went this route over the envelope approach in this PR — applying the OpenAI envelope to @cf/... requests would have changed the native wire contract. Combined, the partner failure you hit is fixed by the routing and the native gap is fixed by #576.

Really appreciate you digging in and filing both the issue and the fix. 🙏