fix: gemini use of vertexai environment variables

Taskfile.yml

@@ -63,7 +63,7 @@ tasks:
   test:
     aliases: [t]
     desc: Run tests
-    cmd: CAGENT_MODELS_GATEWAY= OPENAI_API_KEY= ANTHROPIC_API_KEY= GOOGLE_API_KEY= MISTRAL_API_KEY= GITHUB_TOKEN= go test {{.CLI_ARGS}} ./...
+    cmd: CAGENT_MODELS_GATEWAY= OPENAI_API_KEY= ANTHROPIC_API_KEY= GOOGLE_API_KEY= GOOGLE_GENAI_USE_VERTEXAI= MISTRAL_API_KEY= GITHUB_TOKEN= go test {{.CLI_ARGS}} ./...
 
   build-local:
     desc: Build binaries for local host platform

pkg/config/auto.go

@@ -22,7 +22,11 @@ type providerConfig struct {
 var cloudProviders = []providerConfig{
 	{"anthropic", []string{"ANTHROPIC_API_KEY"}, "ANTHROPIC_API_KEY"},
 	{"openai", []string{"OPENAI_API_KEY"}, "OPENAI_API_KEY"},
-	{"google", []string{"GOOGLE_API_KEY"}, "GOOGLE_API_KEY"},
+	{"google", []string{
+		"GOOGLE_API_KEY",
+		"GEMINI_API_KEY",
+		"GOOGLE_GENAI_USE_VERTEXAI",
+	}, "GOOGLE_API_KEY (or GEMINI_API_KEY, GOOGLE_GENAI_USE_VERTEXAI)"},
 	{"mistral", []string{"MISTRAL_API_KEY"}, "MISTRAL_API_KEY"},
 	{"amazon-bedrock", []string{
 		"AWS_BEARER_TOKEN_BEDROCK",

pkg/config/gather.go

@@ -111,7 +111,12 @@ func addEnvVarsForModelConfig(model *latest.ModelConfig, customProviders map[str
 			requiredEnv["ANTHROPIC_API_KEY"] = true
 		case "google":
 			if model.ProviderOpts["project"] == nil && model.ProviderOpts["location"] == nil {
-				requiredEnv["GOOGLE_API_KEY"] = true
+				if os.Getenv("GOOGLE_GENAI_USE_VERTEXAI") != "" {
+					requiredEnv["GOOGLE_CLOUD_PROJECT"] = true
+					requiredEnv["GOOGLE_CLOUD_LOCATION"] = true
+				} else if _, exist := os.LookupEnv("GEMINI_API_KEY"); !exist {
+					requiredEnv["GOOGLE_API_KEY"] = true
+				}
 			}
 		case "mistral":
 			requiredEnv["MISTRAL_API_KEY"] = true

pkg/model/provider/gemini/client.go

@@ -76,12 +76,22 @@ func NewClient(ctx context.Context, cfg *latest.ModelConfig, env environment.Pro
 				return nil, errors.New("location must be set")
 			}
 
+			backend = genai.BackendVertexAI
+			httpClient = nil // Use default client
+		} else if _, exist := env.Get(ctx, "GOOGLE_GENAI_USE_VERTEXAI"); exist {
+			project, _ = env.Get(ctx, "GOOGLE_CLOUD_PROJECT")
+			location, _ = env.Get(ctx, "GOOGLE_CLOUD_LOCATION")
 			backend = genai.BackendVertexAI
 			httpClient = nil // Use default client
 		} else {
-			apiKey, _ = env.Get(ctx, "GOOGLE_API_KEY")
+			if value, exist := env.Get(ctx, "GEMINI_API_KEY"); exist {
+				apiKey = value
+			}
+			if value, exist := env.Get(ctx, "GOOGLE_API_KEY"); exist {
+				apiKey = value
+			}
 			if apiKey == "" {
-				return nil, errors.New("GOOGLE_API_KEY environment variable is required")
+				return nil, errors.New("GOOGLE_API_KEY or GEMINI_API_KEY environment variable is required")
 			}
 
 			backend = genai.BackendGeminiAPI