fix: retry precommit mysql lock conflicts

internal/storage/mysql/db.go

@@ -51,16 +51,56 @@ func Open(ctx context.Context, dsn string, maxOpen, maxIdle int) (*sql.DB, error
 	return db, nil
 }
 
-// WithTx does not replay callbacks: a failed commit may have succeeded remotely.
-// Callers reconcile by stable operation identity before retrying an ambiguous write.
+const transactionRetryLimit = 2
+
+// WithTx retries only a callback failure caused by a MySQL deadlock or lock wait
+// timeout before COMMIT. It never retries Begin/Commit errors because a commit
+// response may be lost after the database has already applied the transaction;
+// callers must reconcile such an ambiguous write by stable operation identity.
 func WithTx(ctx context.Context, db *sql.DB, fn func(*sql.Tx) error) error {
+	for attempt := 0; attempt <= transactionRetryLimit; attempt++ {
+		err, retryable := withTxAttempt(ctx, db, fn)
+		if err == nil || !retryable || attempt == transactionRetryLimit {
+			return err
+		}
+		if err := waitTransactionRetry(ctx, attempt); err != nil {
+			return err
+		}
+	}
+	return errors.New("transaction retry loop exhausted")
+}
+
+func withTxAttempt(ctx context.Context, db *sql.DB, fn func(*sql.Tx) error) (error, bool) {
 	tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelReadCommitted})
 	if err != nil {
-		return err
+		return err, false
 	}
 	defer tx.Rollback()
 	if err := fn(tx); err != nil {
-		return err
+		return err, retryableTransactionError(err)
+	}
+	if err := tx.Commit(); err != nil {
+		return err, false
+	}
+	return nil, false
+}
+
+func retryableTransactionError(err error) bool {
+	var mysqlErr *driver.MySQLError
+	if !errors.As(err, &mysqlErr) {
+		return false
+	}
+	return mysqlErr.Number == 1205 || mysqlErr.Number == 1213
+}
+
+func waitTransactionRetry(ctx context.Context, attempt int) error {
+	delay := time.Duration(attempt+1) * 25 * time.Millisecond
+	timer := time.NewTimer(delay)
+	defer timer.Stop()
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-timer.C:
+		return nil
 	}
-	return tx.Commit()
 }