Added support for OpenAI-compatible structured output

internal/llm/openai_compatible_client.go

@@ -113,6 +113,13 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 	if req.Target.TopP != 0 {
 		wireReq.TopP = &req.Target.TopP
 	}
+	if req.StructuredOutput != nil {
+		responseFormat, err := toOpenAIResponseFormat(req.StructuredOutput)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
+		}
+		wireReq.ResponseFormat = responseFormat
+	}
 
 	payload, err := json.Marshal(wireReq)
 	if err != nil {
@@ -181,11 +188,12 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 }
 
 type openAIChatRequest struct {
-	Model       string              `json:"model"`
-	Messages    []openAIChatMessage `json:"messages"`
-	Temperature *float64            `json:"temperature,omitempty"`
-	MaxTokens   *int                `json:"max_tokens,omitempty"`
-	TopP        *float64            `json:"top_p,omitempty"`
+	Model          string                `json:"model"`
+	Messages       []openAIChatMessage   `json:"messages"`
+	Temperature    *float64              `json:"temperature,omitempty"`
+	MaxTokens      *int                  `json:"max_tokens,omitempty"`
+	TopP           *float64              `json:"top_p,omitempty"`
+	ResponseFormat *openAIResponseFormat `json:"response_format,omitempty"`
 }
 
 type openAIChatMessage struct {
@@ -203,3 +211,43 @@ type openAIChatResponse struct {
 		TotalTokens      int `json:"total_tokens"`
 	} `json:"usage"`
 }
+
+type openAIResponseFormat struct {
+	Type       string                    `json:"type"`
+	JSONSchema *openAIJSONSchemaEnvelope `json:"json_schema,omitempty"`
+}
+
+type openAIJSONSchemaEnvelope struct {
+	Name   string `json:"name"`
+	Strict bool   `json:"strict"`
+	Schema any    `json:"schema"`
+}
+
+func toOpenAIResponseFormat(spec *domain.StructuredOutputSpec) (*openAIResponseFormat, error) {
+	if spec == nil {
+		return nil, nil
+	}
+
+	switch spec.Type {
+	case domain.StructuredOutputJSONSchema:
+		if spec.JSONSchema == nil {
+			return nil, errors.New("json_schema structured output requires schema payload")
+		}
+		if strings.TrimSpace(spec.JSONSchema.Name) == "" {
+			return nil, errors.New("json_schema structured output requires non-empty schema name")
+		}
+		if spec.JSONSchema.Schema == nil {
+			return nil, errors.New("json_schema structured output requires schema document")
+		}
+		return &openAIResponseFormat{
+			Type: "json_schema",
+			JSONSchema: &openAIJSONSchemaEnvelope{
+				Name:   spec.JSONSchema.Name,
+				Strict: spec.JSONSchema.Strict,
+				Schema: spec.JSONSchema.Schema,
+			},
+		}, nil
+	default:
+		return nil, fmt.Errorf("unsupported structured output type %q", spec.Type)
+	}
+}