parser: fix structured output bug

[pwilkin]

Overview

Fix stupid bug.

Additional information

No, I mean really stupid. Look at the code if you don't believe me.

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: Yes, CC.

Fixes #21571

[pwilkin]

@ggml-org/maintainers need second approval plz

[aldehir]

Sure, if you pass in both json_schema and response_format with {"type": "json_object"}. But aren't you supposed to do this:

response_format={
  "type": "json_schema",
  "json_schema": { ... }
}

Instead of adding it under extra_body?

[ggerganov]

The tests are not passing

[pwilkin]

Yeah, turns out it isn't so simple: I have to handle the case where someone separately set the schema in extra body, but response format in the direct payload AND the case where someone just did json_object without a schema, which should nevertheless result in a generic JSON output format constraint.

Should be good now.