refactor(headers): streamline User-Agent handling and introduce GeminiCLI versioning

internal/misc/header_utils.go

@@ -10,13 +10,43 @@ import (
 	"strings"
 )
 
+const (
+	// GeminiCLIVersion is the version string reported in the User-Agent for upstream requests.
+	GeminiCLIVersion = "0.31.0"
+
+	// GeminiCLIApiClientHeader is the value for the X-Goog-Api-Client header sent to the Gemini CLI upstream.
+	GeminiCLIApiClientHeader = "google-genai-sdk/1.41.0 gl-node/v22.19.0"
+)
+
+// geminiCLIOS maps Go runtime OS names to the Node.js-style platform strings used by Gemini CLI.
+func geminiCLIOS() string {
+	switch runtime.GOOS {
+	case "windows":
+		return "win32"
+	default:
+		return runtime.GOOS
+	}
+}
+
+// geminiCLIArch maps Go runtime architecture names to the Node.js-style arch strings used by Gemini CLI.
+func geminiCLIArch() string {
+	switch runtime.GOARCH {
+	case "amd64":
+		return "x64"
+	case "386":
+		return "x86"
+	default:
+		return runtime.GOARCH
+	}
+}
+
 // GeminiCLIUserAgent returns a User-Agent string that matches the Gemini CLI format.
 // The model parameter is included in the UA; pass "" or "unknown" when the model is not applicable.
 func GeminiCLIUserAgent(model string) string {
 	if model == "" {
 		model = "unknown"
 	}
-	return fmt.Sprintf("GeminiCLI/1.0.0/%s (%s; %s)", model, runtime.GOOS, runtime.GOARCH)
+	return fmt.Sprintf("GeminiCLI/%s/%s (%s; %s)", GeminiCLIVersion, model, geminiCLIOS(), geminiCLIArch())
 }
 
 // ScrubProxyAndFingerprintHeaders removes all headers that could reveal
@@ -93,4 +123,3 @@ func EnsureHeader(target http.Header, source http.Header, key, defaultValue stri
 		target.Set(key, val)
 	}
 }
-