Function request_structured_output 

pub async fn request_structured_output(
    provider: &dyn LlmProvider,
    structured_request: &StructuredOutputRequest,
) -> Result<Value, RunnerError>

Request structured JSON output from any provider, with schema validation and retry.

Flow

1. Append schema instructions to the system message
2. Call provider.complete() and extract JSON from the response
3. Validate against the schema
4. On failure, append errors as user feedback and retry up to max_retries
5. After exhaustion, return RunnerError::external_service

Errors

Returns RunnerError if the provider fails or validation is exhausted.