Fix: handle steps in /v1/images/generations endpoint

[aurorianus]

Summary

The /v1/images/generations endpoint was ignoring the steps field in the request body. The parameter was parsed from the JSON but never applied to sample_params.sample_steps, so all requests fell back to the server default regardless of what the client sent.

Since the field is already parsed, this is a one-line fix — the client's value just wasn't being used. Resolves the steps issue reported in #1159.

Related Issue / Discussion

#1159
#1050

Additional Information

Before: always uses server default regardless of steps value

curl -X POST http://localhost:8080/v1/images/generations
-H "Content-Type: application/json"
-d '{"prompt":"test","steps":5,"n":1}'

Would produce the same output as steps=20
After: respects the steps value

curl -X POST http://localhost:8080/v1/images/generations
-H "Content-Type: application/json"
-d '{"prompt":"test","steps":5,"n":1}'

Obeys steps instruction, 5 inference steps

Checklist

• I have read and confirmed this PR follows the contribution guidelines.

[wbruna]

/v1/images/generations is supposed to implement the OpenAI API, which does not support a steps field:
https://developers.openai.com/api/reference/resources/images/methods/generate

The number of steps should be specified through the sd_cpp_extra_args prompt extension.

[leejet]

Thanks for the PR.

I don’t think we should support steps as a top-level field in /v1/images/generations.

This endpoint is intended to stay compatible with the OpenAI-style image API. steps is not an official OpenAI Images API request field, so accepting it at the top level would expand the compatibility API with non-OpenAI parameters.

For stable-diffusion.cpp-specific controls, please use the existing extension mechanism: sd_cpp_extra_args. For example:

{
  "prompt": "test <sd_cpp_extra_args>{\"sample_params\":{\"sample_steps\":5}}</sd_cpp_extra_args>",
  "n": 1
}

See the documented extension mechanism here:
examples/server/api.md#sd_cpp_extra_args

So I’m going to close this PR as not planned. Thanks again for taking the time to investigate and submit the fix.

[aurorianus]

ah hah! Got it. Ty for the explanation guys