feat(api): add "max" reasoning depth and service_tiers to Codex client models

- Introduced a new "max" level for reasoning depth in Codex client model configuration, providing maximum problem-solving capability.
- Added `service_tiers` field to model responses for better tier categorization.
- Updated unit tests to validate the inclusion and default behavior of `service_tiers` and the new "max" reasoning depth.

internal/api/server_test.go

@@ -531,6 +531,10 @@ func TestModelsWithClientVersionReturnsCodexCatalog(t *testing.T) {
 	if got, _ := custom["prefer_websockets"].(bool); got {
 		t.Fatalf("custom prefer_websockets = %v, want false", custom["prefer_websockets"])
 	}
+	customServiceTiers, ok := custom["service_tiers"].([]any)
+	if !ok || len(customServiceTiers) != 0 {
+		t.Fatalf("expected custom model service_tiers = [], got %#v", custom["service_tiers"])
+	}
 	if _, ok := custom["apply_patch_tool_type"]; ok {
 		t.Fatal("expected custom model to omit apply_patch_tool_type")
 	}

sdk/api/handlers/openai/codex_client_models.go

@@ -26,6 +26,7 @@ var codexClientAllowedReasoningLevels = map[string]struct{}{
 	"medium": {},
 	"high":   {},
 	"xhigh":  {},
+	"max":    {},
 }
 
 func (h *OpenAIAPIHandler) codexClientModelsResponse() map[string]any {
@@ -132,6 +133,7 @@ func applyCodexClientModelMetadata(entry map[string]any, id string, model map[st
 	entry["description"] = description
 	entry["priority"] = 100
 	entry["prefer_websockets"] = false
+	entry["service_tiers"] = []any{}
 	delete(entry, "apply_patch_tool_type")
 	delete(entry, "upgrade")
 	delete(entry, "availability_nux")
@@ -249,6 +251,8 @@ func codexClientReasoningDescription(level string) string {
 		return "Greater reasoning depth for complex problems"
 	case "xhigh":
 		return "Extra high reasoning depth for complex problems"
+	case "max":
+		return "Maximum available reasoning depth for complex problems"
 	default:
 		return level
 	}