feat(api): add Codex client models support for OpenAI API

- Introduced Codex client models framework in `openai` package.
- Added JSON-based model definitions (`codex_client_models.json`) for Codex, including metadata, reasoning levels, and configuration options.
- Implemented handlers to load, clone, and build Codex client models with support for visibility overrides and metadata application.
- Enabled sorting and prioritization of models based on configuration or runtime criteria.
- Added utility functions for managing and validating model attributes.

sdk/api/handlers/openai/openai_handlers.go

@@ -8,6 +8,7 @@ package openai
 
 import (
 	"context"
+	_ "embed"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -29,6 +30,9 @@ type OpenAIAPIHandler struct {
 	*handlers.BaseAPIHandler
 }
 
+//go:embed codex_client_models.json
+var codexClientModelsJSON []byte
+
 // NewOpenAIAPIHandler creates a new OpenAI API handlers instance.
 // It takes an BaseAPIHandler instance as input and returns an OpenAIAPIHandler.
 //
@@ -59,6 +63,11 @@ func (h *OpenAIAPIHandler) Models() []map[string]any {
 // It returns a list of available AI models with their capabilities
 // and specifications in OpenAI-compatible format.
 func (h *OpenAIAPIHandler) OpenAIModels(c *gin.Context) {
+	if _, ok := c.Request.URL.Query()["client_version"]; ok {
+		c.JSON(http.StatusOK, h.codexClientModelsResponse())
+		return
+	}
+
 	// Get all available models
 	allModels := h.Models()