feat(chatpb): backup gemini.pb before saving

config.go

@@ -5,8 +5,10 @@ package chatpb
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
+	"time"
 
 	"go.wit.com/lib/protobuf/bugpb"
 	"go.wit.com/log"
@@ -56,6 +58,21 @@ func (all *Chats) ConfigSave() error {
 		}
 		return err
 	}
+
+	// --- Backup Logic ---
+	filename := filepath.Join(os.Getenv("GEMINI_HOME"), "gemini.pb")
+	if _, err := os.Stat(filename); err == nil {
+		// File exists, so back it up.
+		dir := filepath.Dir(filename)
+		timestamp := time.Now().Format("20060102-150405")
+		backupFilename := fmt.Sprintf("gemini.%s.pb", timestamp)
+		backupPath := filepath.Join(dir, backupFilename)
+		if err := os.Rename(filename, backupPath); err != nil {
+			log.Warn("Could not backup config file:", err)
+		}
+	}
+	// --- End Backup Logic ---
+
 	if err := configWrite("gemini.pb", data); err != nil {
 		log.Infof("chatpb.ConfigSave() failed len(Chats)=%d bytes=%d", len(cleanChats.Chats), len(data))
 		return err