feat(server/db): 多库(3/4)— Dialect 抽象(upsert/锁)+ 合并 directory_version

- db.Dialect:LockForUpdate(mysql "FOR UPDATE" / sqlite "")、Upsert(中性
  EXCLUDED.col → mysql VALUES()/ sqlite excluded.);DialectForDB 从连接驱动推导
- 9 处 ON DUPLICATE KEY、11 处 FOR UPDATE 全走 dialect;sqlite 靠 _txlock=
  immediate 取得 BEGIN IMMEDIATE 悲观锁等价语义
- directory_version 三处重复合并为 store.BumpDirectoryVersion(dialect 感知)
- 这些文件同时含(2/4)的 UTC→Go 改动(与 upsert/锁同语句交错,无法拆分)
- 顺带:usage 的 FIELD()、codes 的 DATE_ADD/GREATEST 续期、nodes 的
  UNIX_TIMESTAMP、NULLIF 等 MySQL 专属构造一并退回 Go/可移植写法

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/codes/store.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"strings"
 	"time"
+
+	dbx "github.com/wangjia/pangolin/server/internal/db"
 )
 
 // PlanCode represents a plan tier.
@@ -76,11 +78,12 @@ type BatchRow struct {
 // outside an explicit transaction; methods that accept a *sql.Tx run within
 // that transaction.
 type Store struct {
-	db *sql.DB
+	db      *sql.DB
+	dialect dbx.Dialect
 }
 
-// NewStore creates a Store backed by the given MySQL connection pool.
-func NewStore(db *sql.DB) *Store { return &Store{db: db} }
+// NewStore creates a Store backed by the given connection pool (MySQL or SQLite).
+func NewStore(db *sql.DB) *Store { return &Store{db: db, dialect: dbx.DialectForDB(db)} }
 
 // --------------------------------------------------------------------------
 // Batch and code creation (used by Service.CreateBatch and webhook)
@@ -88,10 +91,14 @@ func NewStore(db *sql.DB) *Store { return &Store{db: db} }
 
 // CreateBatch inserts a new code_batches row and returns its ID.
 func (s *Store) CreateBatch(ctx context.Context, channel BatchChannel, createdBy, note string) (int64, error) {
+	var notePtr *string
+	if note != "" {
+		notePtr = &note
+	}
 	res, err := s.db.ExecContext(ctx,
 		`INSERT INTO code_batches (channel, created_by, note, created_at)
-		 VALUES (?, ?, NULLIF(?, ''), UTC_TIMESTAMP(6))`,
-		string(channel), createdBy, note)
+		 VALUES (?, ?, ?, ?)`,
+		string(channel), createdBy, notePtr, time.Now().UTC())
 	if err != nil {
 		return 0, fmt.Errorf("store.CreateBatch: %w", err)
 	}
@@ -133,7 +140,7 @@ func (s *Store) FindCodeByHashForUpdate(ctx context.Context, tx *sql.Tx, hash st
 		 FROM codes c
 		 JOIN plans p ON p.id = c.plan_id
 		 WHERE c.code_hash = ?
-		 FOR UPDATE`,
+		 `+s.dialect.LockForUpdate(),
 		hash)
 
 	var cr CodeRow
@@ -151,9 +158,9 @@ func (s *Store) FindCodeByHashForUpdate(ctx context.Context, tx *sql.Tx, hash st
 // MarkRedeemed updates a codes row to status='redeemed' within tx.
 func (s *Store) MarkRedeemed(ctx context.Context, tx *sql.Tx, codeID, userID int64) error {
 	_, err := tx.ExecContext(ctx,
-		`UPDATE codes SET status='redeemed', redeemed_by=?, redeemed_at=UTC_TIMESTAMP(6)
+		`UPDATE codes SET status='redeemed', redeemed_by=?, redeemed_at=?
 		 WHERE id=? AND status='unused'`,
-		userID, codeID)
+		userID, time.Now().UTC(), codeID)
 	if err != nil {
 		return fmt.Errorf("store.MarkRedeemed: %w", err)
 	}
@@ -181,9 +188,9 @@ func (s *Store) GetActiveSubscriptions(ctx context.Context, tx *sql.Tx, userID i
 		`SELECT s.id, s.user_id, s.plan_id, p.code, s.expires_at, s.source
 		 FROM subscriptions s
 		 JOIN plans p ON p.id = s.plan_id
-		 WHERE s.user_id=? AND s.expires_at > UTC_TIMESTAMP(6)
+		 WHERE s.user_id=? AND s.expires_at > ?
 		 ORDER BY s.expires_at DESC`,
-		userID)
+		userID, time.Now().UTC())
 	if err != nil {
 		return nil, fmt.Errorf("store.GetActiveSubscriptions: %w", err)
 	}
@@ -201,15 +208,24 @@ func (s *Store) GetActiveSubscriptions(ctx context.Context, tx *sql.Tx, userID i
 }
 
 // ExtendSubscription sets expires_at to max(current_expires_at, now) + duration.
-// Called inside the redeem transaction.
+// Called inside the redeem transaction. The base date is computed in Go (the
+// subscription row is read inside the locked redeem tx, then updated) — portable
+// across engines and avoids DB-side DATE_ADD/GREATEST.
 func (s *Store) ExtendSubscription(ctx context.Context, tx *sql.Tx, subID int64, durationDays int) error {
+	var current time.Time
+	if err := tx.QueryRowContext(ctx,
+		`SELECT expires_at FROM subscriptions WHERE id=?`, subID).Scan(&current); err != nil {
+		return fmt.Errorf("store.ExtendSubscription read: %w", err)
+	}
+	base := time.Now().UTC()
+	if current.After(base) {
+		base = current.UTC()
+	}
+	newExpiry := base.AddDate(0, 0, durationDays)
+
 	_, err := tx.ExecContext(ctx,
-		`UPDATE subscriptions
-		 SET expires_at = DATE_ADD(
-		       GREATEST(expires_at, UTC_TIMESTAMP(6)),
-		       INTERVAL ? DAY)
-		 WHERE id=?`,
-		durationDays, subID)
+		`UPDATE subscriptions SET expires_at = ? WHERE id=?`,
+		newExpiry, subID)
 	if err != nil {
 		return fmt.Errorf("store.ExtendSubscription: %w", err)
 	}
@@ -235,8 +251,8 @@ func (s *Store) CreateSubscription(
 
 	res, err := tx.ExecContext(ctx,
 		`INSERT INTO subscriptions (user_id, plan_id, expires_at, source, created_at)
-		 VALUES (?, ?, ?, 'code', UTC_TIMESTAMP(6))`,
-		userID, planID, expiresAt)
+		 VALUES (?, ?, ?, 'code', ?)`,
+		userID, planID, expiresAt, now)
 	if err != nil {
 		return 0, fmt.Errorf("store.CreateSubscription: %w", err)
 	}
@@ -255,14 +271,15 @@ func (s *Store) WriteAuditLog(ctx context.Context, tx *sql.Tx, actor, action, ta
 	if metaJSON == "" {
 		metaJSON = "null"
 	}
+	now := time.Now().UTC()
 	if tx != nil {
 		_, err = tx.ExecContext(ctx,
-			`INSERT INTO audit_log (actor, action, target, meta, at) VALUES (?, ?, ?, ?, UTC_TIMESTAMP(6))`,
-			actor, action, target, metaJSON)
+			`INSERT INTO audit_log (actor, action, target, meta, at) VALUES (?, ?, ?, ?, ?)`,
+			actor, action, target, metaJSON, now)
 	} else {
 		_, err = s.db.ExecContext(ctx,
-			`INSERT INTO audit_log (actor, action, target, meta, at) VALUES (?, ?, ?, ?, UTC_TIMESTAMP(6))`,
-			actor, action, target, metaJSON)
+			`INSERT INTO audit_log (actor, action, target, meta, at) VALUES (?, ?, ?, ?, ?)`,
+			actor, action, target, metaJSON, now)
 	}
 	if err != nil {
 		return fmt.Errorf("store.WriteAuditLog: %w", err)