Structured chat does not work with Groq models

[CoryMcCartan]

Brand new to ellmer. This code seemed to work with other model providers, but not Groq:

chat = chat_groq(model="openai/gpt-oss-20b")
chat$chat_structured("Is Boston the capital of MA?", type=type_boolean())
#> Error in `req_perform()`:
#> ! HTTP 400 Bad Request.
#> ℹ invalid JSON schema for response_format: 'structured_data':
#>   `additionalProperties:false` must be set on every object
#> Run `rlang::last_trace()` to see where the error occurred.

Happy to submit a PR if this is e.g. a recent change in their API.

[CoryMcCartan]

Apologies, it's right in the provider documentation that this is not supposed to work!
However, I am able to successfully get a structured completion with a raw curl request:

Details

curl "https://api.groq.com/openai/v1/chat/completions" \
  -X POST \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer ${GROQ_API_KEY}" \
  -d '{
         "messages": [
           {
             "role": "system",
             "content": "Answer the question with true for yes and false for no."
           },
           {
             "role": "user",
             "content": "Is Boston the capital of MA?"
           }
         ],
         "model": "openai/gpt-oss-20b",
         "temperature": 1,
         "max_completion_tokens": 100,
         "top_p": 1,
         "stream": false,
         "reasoning_effort": "low",
         "response_format": {
           "type": "json_schema",
           "json_schema": {
               "name": "yes_no",
               "schema": {
                   "type": "object",
                   "properties": {
                       "answer": {"type": "boolean"}
                   },
                   "required": ["answer"],
                   "additionalProperties": false
               },
               "strict": false
           }
         },
         "stop": null
       }'

So, still happy to make a PR if it seems like it's possible to add support for this.

[hadley]

Yes, a PR would be great!