fix: 修复写队列 busy 恢复、关闭安全、备份与配置构建问题

internal/store/db.go

@@ -1,6 +1,7 @@
 package store
 
 import (
+	"context"
 	"database/sql"
 	"fmt"
 	"os"
@@ -10,7 +11,8 @@ import (
 	_ "modernc.org/sqlite"
 )
 
-const dbFileName = "nixmsg.db"
+// DBFileName 是数据目录下的主库文件名。
+const DBFileName = "nixmsg.db"
 
 // DB 持有读写连接与写入队列。
 type DB struct {
@@ -25,7 +27,7 @@ func Open(dataDir, synchronous string) (*DB, error) {
 	if err := os.MkdirAll(dataDir, 0o755); err != nil {
 		return nil, fmt.Errorf("mkdir data_dir: %w", err)
 	}
-	dbPath := filepath.Join(dataDir, dbFileName)
+	dbPath := filepath.Join(dataDir, DBFileName)
 	existed, err := fileExists(dbPath)
 	if err != nil {
 		return nil, err
@@ -69,10 +71,41 @@ func (d *DB) Close() error {
 	return first
 }
 
+// Checkpoint 在写 goroutine 上执行 wal_checkpoint(TRUNCATE)。
+func (d *DB) Checkpoint(ctx context.Context) error {
+	if d == nil || d.Queue == nil {
+		return fmt.Errorf("store: not open")
+	}
+	return d.Queue.Checkpoint(ctx)
+}
+
 // OpenWriter 按 DEVELOPMENT 7.7 打开写连接（带 _txlock=immediate，MaxOpenConns=1）。
 func OpenWriter(dataDir, synchronous string) (*sql.DB, error) {
-	if err := os.MkdirAll(dataDir, 0o755); err != nil {
-		return nil, fmt.Errorf("mkdir data_dir: %w", err)
+	return openWriter(dataDir, synchronous, true)
+}
+
+// OpenExistingWriter 打开已有库的写连接，不创建数据目录；库文件不存在时返回错误。
+func OpenExistingWriter(dataDir, synchronous string) (*sql.DB, error) {
+	dbPath := filepath.Join(dataDir, DBFileName)
+	ok, err := fileExists(dbPath)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		abs, absErr := filepath.Abs(dbPath)
+		if absErr != nil {
+			abs = dbPath
+		}
+		return nil, fmt.Errorf("database not found: %s", abs)
+	}
+	return openWriter(dataDir, synchronous, false)
+}
+
+func openWriter(dataDir, synchronous string, mkdir bool) (*sql.DB, error) {
+	if mkdir {
+		if err := os.MkdirAll(dataDir, 0o755); err != nil {
+			return nil, fmt.Errorf("mkdir data_dir: %w", err)
+		}
 	}
 	dsn, err := buildDSN(dataDir, synchronous, true)
 	if err != nil {
@@ -116,7 +149,7 @@ func buildDSN(dataDir, synchronous string, writer bool) (string, error) {
 	if sync != "FULL" && sync != "NORMAL" {
 		return "", fmt.Errorf("invalid sqlite_synchronous: %s", synchronous)
 	}
-	dbPath := filepath.ToSlash(filepath.Join(dataDir, dbFileName))
+	dbPath := filepath.ToSlash(filepath.Join(dataDir, DBFileName))
 	dsn := fmt.Sprintf(
 		"file:%s?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)&_pragma=synchronous(%s)&_pragma=foreign_keys(ON)&_pragma=secure_delete(ON)",
 		dbPath,