OpenRouter structured handler should use json_schema and preserve structured_outputs

[mistermantas]

Hi, I think the OpenRouter structured-output handler may be sending the wrong request shape.

OpenRouter’s structured output docs show strict schema output using:

{
  "response_format": {
    "type": "json_schema",
    "json_schema": {
      "name": "...",
      "strict": true,
      "schema": {}
    }
  },
  "structured_outputs": true
}

But Prism’s OpenRouter structured handler appears to send the schema under response_format while using type: "json_object".

That means OpenRouter treats it as normal JSON mode, not strict schema-constrained output. Some models still behave okay, but others return empty content, unstructured content, or schema-shaped but unreliable output.

Suggested fix:

'response_format' => [
    'type' => 'json_schema',
    'json_schema' => [
        'name' => $request->schema()->name(),
        'strict' => true,
        'schema' => $request->schema()->toArray(),
    ],
],
'structured_outputs' => $request->providerOptions('structured_outputs') ?? true,

It may also be worth documenting that callers can pass:

'provider' => [
    'require_parameters' => true,
],

for OpenRouter so it does not route the request to an endpoint that ignores unsupported structured-output parameters.

Relevant OpenRouter docs:

• https://openrouter.ai/docs/guides/features/structured-outputs
• https://openrouter.ai/docs/api/reference/parameters
• https://openrouter.ai/docs/guides/routing/provider-selection

This seems separate from plain JSON mode. response_format carries the schema, while structured_outputs is a separate supported parameter/capability flag.