feat(models): add hardcoded GPT-Image-2 model support in Codex

- Added `GPT-Image-2` as a built-in model to avoid dependency on remote updates for Codex.
- Updated model tier functions (`CodexFree`, `CodexTeam`, etc.) to include built-in models via `WithCodexBuiltins`.
- Introduced new handlers for image generation and edit operations under `OpenAIAPIHandler`.
- Extended tests to validate 503 response for unsupported image model requests.

internal/api/server.go

@@ -344,6 +344,8 @@ func (s *Server) setupRoutes() {
 		v1.GET("/models", s.unifiedModelsHandler(openaiHandlers, claudeCodeHandlers))
 		v1.POST("/chat/completions", openaiHandlers.ChatCompletions)
 		v1.POST("/completions", openaiHandlers.Completions)
+		v1.POST("/images/generations", openaiHandlers.ImagesGenerations)
+		v1.POST("/images/edits", openaiHandlers.ImagesEdits)
 		v1.POST("/messages", claudeCodeHandlers.ClaudeMessages)
 		v1.POST("/messages/count_tokens", claudeCodeHandlers.ClaudeCountTokens)
 		v1.GET("/responses", openaiResponsesHandlers.ResponsesWebsocket)

internal/registry/model_definitions.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 )
 
+const codexBuiltinImageModelID = "gpt-image-2"
+
 // staticModelsJSON mirrors the top-level structure of models.json.
 type staticModelsJSON struct {
 	Claude      []*ModelInfo `json:"claude"`
@@ -48,22 +50,22 @@ func GetAIStudioModels() []*ModelInfo {
 
 // GetCodexFreeModels returns model definitions for the Codex free plan tier.
 func GetCodexFreeModels() []*ModelInfo {
-	return cloneModelInfos(getModels().CodexFree)
+	return WithCodexBuiltins(cloneModelInfos(getModels().CodexFree))
 }
 
 // GetCodexTeamModels returns model definitions for the Codex team plan tier.
 func GetCodexTeamModels() []*ModelInfo {
-	return cloneModelInfos(getModels().CodexTeam)
+	return WithCodexBuiltins(cloneModelInfos(getModels().CodexTeam))
 }
 
 // GetCodexPlusModels returns model definitions for the Codex plus plan tier.
 func GetCodexPlusModels() []*ModelInfo {
-	return cloneModelInfos(getModels().CodexPlus)
+	return WithCodexBuiltins(cloneModelInfos(getModels().CodexPlus))
 }
 
 // GetCodexProModels returns model definitions for the Codex pro plan tier.
 func GetCodexProModels() []*ModelInfo {
-	return cloneModelInfos(getModels().CodexPro)
+	return WithCodexBuiltins(cloneModelInfos(getModels().CodexPro))
 }
 
 // GetKimiModels returns the standard Kimi (Moonshot AI) model definitions.
@@ -76,6 +78,71 @@ func GetAntigravityModels() []*ModelInfo {
 	return cloneModelInfos(getModels().Antigravity)
 }
 
+// WithCodexBuiltins injects hard-coded Codex-only model definitions that should
+// not depend on remote models.json updates. Built-ins replace any matching IDs
+// already present in the provided slice.
+func WithCodexBuiltins(models []*ModelInfo) []*ModelInfo {
+	return upsertModelInfos(models, codexBuiltinImageModelInfo())
+}
+
+func codexBuiltinImageModelInfo() *ModelInfo {
+	return &ModelInfo{
+		ID:          codexBuiltinImageModelID,
+		Object:      "model",
+		Created:     1704067200, // 2024-01-01
+		OwnedBy:     "openai",
+		Type:        "openai",
+		DisplayName: "GPT Image 2",
+		Version:     codexBuiltinImageModelID,
+	}
+}
+
+func upsertModelInfos(models []*ModelInfo, extras ...*ModelInfo) []*ModelInfo {
+	if len(extras) == 0 {
+		return models
+	}
+
+	extraIDs := make(map[string]struct{}, len(extras))
+	extraList := make([]*ModelInfo, 0, len(extras))
+	for _, extra := range extras {
+		if extra == nil {
+			continue
+		}
+		id := strings.TrimSpace(extra.ID)
+		if id == "" {
+			continue
+		}
+		key := strings.ToLower(id)
+		if _, exists := extraIDs[key]; exists {
+			continue
+		}
+		extraIDs[key] = struct{}{}
+		extraList = append(extraList, cloneModelInfo(extra))
+	}
+
+	if len(extraList) == 0 {
+		return models
+	}
+
+	filtered := make([]*ModelInfo, 0, len(models)+len(extraList))
+	for _, model := range models {
+		if model == nil {
+			continue
+		}
+		id := strings.TrimSpace(model.ID)
+		if id == "" {
+			continue
+		}
+		if _, exists := extraIDs[strings.ToLower(id)]; exists {
+			continue
+		}
+		filtered = append(filtered, model)
+	}
+
+	filtered = append(filtered, extraList...)
+	return filtered
+}
+
 // cloneModelInfos returns a shallow copy of the slice with each element deep-cloned.
 func cloneModelInfos(models []*ModelInfo) []*ModelInfo {
 	if len(models) == 0 {