feat: add DB backup with consistent BoltDB snapshots

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

store/backup.go

@@ -0,0 +1,40 @@
+package store
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	bolt "go.etcd.io/bbolt"
+)
+
+// Backup creates a consistent snapshot of the database in destDir.
+// Returns the path to the backup file.
+func (d *DB) Backup(destDir string) (string, error) {
+	if err := os.MkdirAll(destDir, 0755); err != nil {
+		return "", fmt.Errorf("create backup dir: %w", err)
+	}
+
+	timestamp := time.Now().Format("20060102-150405")
+	filename := fmt.Sprintf("catacombs-%s.db", timestamp)
+	destPath := filepath.Join(destDir, filename)
+
+	f, err := os.Create(destPath)
+	if err != nil {
+		return "", fmt.Errorf("create backup file: %w", err)
+	}
+	defer f.Close()
+
+	// BoltDB View transaction provides a consistent snapshot
+	err = d.db.View(func(tx *bolt.Tx) error {
+		_, err := tx.WriteTo(f)
+		return err
+	})
+	if err != nil {
+		os.Remove(destPath)
+		return "", fmt.Errorf("backup write: %w", err)
+	}
+
+	return destPath, nil
+}

store/backup_test.go

@@ -0,0 +1,68 @@
+package store
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestBackup(t *testing.T) {
+	tmpDir := t.TempDir()
+	dbPath := filepath.Join(tmpDir, "test.db")
+	db, err := Open(dbPath)
+	if err != nil {
+		t.Fatalf("failed to open db: %v", err)
+	}
+	defer db.Close()
+
+	if err := db.SaveProfile("fp1", "player1"); err != nil {
+		t.Fatalf("failed to save profile: %v", err)
+	}
+
+	backupDir := filepath.Join(tmpDir, "backups")
+
+	backupPath, err := db.Backup(backupDir)
+	if err != nil {
+		t.Fatalf("backup failed: %v", err)
+	}
+
+	if _, err := os.Stat(backupPath); os.IsNotExist(err) {
+		t.Fatal("backup file does not exist")
+	}
+
+	base := filepath.Base(backupPath)
+	if !strings.HasPrefix(base, "catacombs-") || !strings.HasSuffix(base, ".db") {
+		t.Fatalf("unexpected backup filename: %s", base)
+	}
+
+	backupDB, err := Open(backupPath)
+	if err != nil {
+		t.Fatalf("failed to open backup: %v", err)
+	}
+	defer backupDB.Close()
+
+	name, err := backupDB.GetProfile("fp1")
+	if err != nil {
+		t.Fatalf("failed to read from backup: %v", err)
+	}
+	if name != "player1" {
+		t.Fatalf("expected player1, got %s", name)
+	}
+}
+
+func TestBackupCreatesDir(t *testing.T) {
+	tmpDir := t.TempDir()
+	dbPath := filepath.Join(tmpDir, "test.db")
+	db, err := Open(dbPath)
+	if err != nil {
+		t.Fatalf("failed to open db: %v", err)
+	}
+	defer db.Close()
+
+	backupDir := filepath.Join(tmpDir, "nested", "backups")
+	_, err = db.Backup(backupDir)
+	if err != nil {
+		t.Fatalf("backup with nested dir failed: %v", err)
+	}
+}